C & T Harris: The Complete Collection
By Eben van Tonder
19 June 2021
Photo from our Solheim apartment in Johannesburg. A multi-needle injector from the Harris factory.
Introduction
The first article I did on C&T Harris appeared on 20 May 2015. Over the years I updated and expanded it. Susan Boddington, a historian and author from Wiltshire was the first person to become a valued collaborator. She continues to work closely with me. Mike Caswell who grew up in Calne joined the efforts with a wealth of first-hand information and sharing the results of dedicated research. There are many others from all over the world.
When I ran the Johannesburg company, Van Wyngaardt with Paul Fickling for Etienne Lotter and his Etlin International, my year and a half in Johannesburg gave me the opportunity to complete the first major draft of my book on the history of bacon, Bacon & the Art of Living. My daughter, Lauren, joined me when she was employed to manage the in-store campaigns for Van Wyngaardt and for weeks on end I would get back to our Solheim apartment where she would prepare dinner while I would write. It gave me the chance to expand this early article into several chapters in my book.
When I contracted Covid a second time in 2021, as sick as I was, I saw an opportunity for another major revision. By this weekend, still recovering, I managed to re-work all the chapters dealing with the Harris operation in Calne. In my book, I presented the story in narrative form. This style may be annoying to some but it proved to a very useful investigative technique as it forced me to think through every process in the 1st person and allowed me to see relationships between seemingly unconnected bits of technology in a completely new and holistic way. By, as it were, “living in the moment,” I gained insights I would never have seen if I simply reported the features of each system separately.
From Bacon & the Art of Living
Below is the list of chapters dealing specifically with the Harris operation for those who desire to confine their enquiry to Harris.
One very important additional chapter must be grouped here. Chapter 10.14 Dublin and the Injection of Meat deals with the invention of stitch pumping and arterial injection in particular. Harris used this system for many years. It places the invention of using a needle to inject brine into meat in the right time when Harris started using stitch pumping which directly resulted in the invention of sweet cured bacon. In this chapter I also develops the benefits of pre-rigour meat injection in great detail. It must logically therefore be grouped with the general work on Harris bacon as it shows the invention of processes which was either pioneered by them or used, in cases where it was invented by others.
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Join Gil and Eben every week in the Charc’ Tank where we talk meat!
Don’t expect an academic discussion. Having said that, we are not scared of scientific inquiry!
We talk informally about that which we love: meat!
We dont always stick strictly to a point by point script or even to any particular subject even though we broadly thread every discussion around a central theme.
Gil started his meat journey in 1978 when he was just five years old. The first piece of “furniture” he bought with his own money when he moved out of his mother’s home in 1994 was a WEBER Kettle BBQ.
For the past 17 years, Gil has been curing meats as a hobbyist and commercial curesmith. In 2019 Gil, with his family, moved to Poland, where he is now focused on building a digital media business promoting the curing of meat.
Eben created Woodys Consumer Brands in 2008 with Oscar Klynveld which grew to SA’s largest 3rd party bacon producer. He left Woodys in 2018 to focus on fine emulsion sausages and other interesting meat research projects. He writes extensively on the meat industry and continues to works in the trade as an independent consultant. He lives in Cape Town.
I interpose after every technical consideration with photos from the last 18 months of work and some comments on the progression of our story. It serves as a repository of my private recollections of the project.
“Between April 2018 and August 2019, I worked for the Johannesburg meat processor, Van Wyngaardt. I adjusted their pure meat block of Russians by adding soy. So started a quest to produce a high quality, low-cost Russian which consumed me for the past 18 months. I started thinking about Russians from scratch.”(VWG subsequently returned to a pure meat Russian)
The photo on the left is of my daughter Lauren and me at our Solheim home in Johannesburg. She joined me to provide impetus to VWG’s in-store work which she did with passion and excellence. The photos below are of Minette and Brussouw during the lockdown, the Johannesburg skyline seen on the last day I spend at VWG and a trolley of VWG Russians.
Fine Meat Mixes vs Course Mixes
The Russian sausage, similar to polony, developed as a way to work away unused scraps of leftover meat in the butchery. By “leftover meats” we do not mean inferior meat. It is inevitable that bits of meat are left after the meat was trimmed neatly and these scraps are of the highest quality. It was the practice in butcheries across the country in the 1800s and early 1900s to mince any leftover offal and discarded sausage meat very finely to be cooked in casings from animal intestines and to sell it as polony (The Origins of Polony). The reason for reducing various meat scraps to the same physical state was to create something that looks uniform. Larger and small bits of high-quality meat from all the species were combined into Russians.
The difference between polony and Russians was that polony would contain only finely ground meat but Russians would contain the same finely ground meat as a base but larger bits of meat would be added called “showpieces.” Russians would be viewed as of a higher quality than polony.
Over the years technology improved to chop the meat into smaller particles. Meat grinders have been generally available for many years and different plate sizes were made available to adjust the coarseness. The smallest plate size would be used for the fine meat base. Later bowl cutters were introduced being a rotating bowl with a set of knives chopping the meat into even smaller particles. This meant that some butchers had very smooth and finely chopped meat as the base for the Russians and those who could not afford the new equipment continued doing it all by hand or through a meat grinder. Some of these butchers could afford the new high-speed equipment but preferred to continue doing the mincing of the meat by hand as some still prefer to this day. Doing it by hand or only with a meat grinder yields understandably a less smooth meat base than if it’s done with more sophisticated equipment.
Two distinct styles of Russians developed. One with a very smooth texture for the meat base into which the large showpieces are embedded and another with an altogether courser meat base. Which one to prefer became completely a matter of taste and any perception that the Russian with a smoother base is inferior to a more course base is unfounded.
“My personal quest to understand Russians better intensified during the nationwide Covid-19 lockdown. My good friend, Dr Francois Mellett helped me to understand the basics. An equally good friend from Canada, Robert Goodrick, arguably the best butcher on planet earth, schooled me in old-school butchers techniques and how to make Russians without bowl cutters. In between the help from Francois and Robert, the team from Deli Spices was a great inspiration opening my eyes to the power of proper mixing!”
Photo on the right is an iconic photo when Francois and I sneaked some seawater away for desperate fish. More I can not say. 😉 Bottom left is Robert Goodrick, the middle photo is me, Arno Pienaar and Tshepo Setshogoe, a legendary Russian maker! As I recall, the trials with Deli was done a week before lockdown in April. We tested the overall water-holding of fist-size trip pork trim pieces and a simple Russian recipe without a fine meat paste, using only the meat grinder. If we go out and over many beers, I will tell you the story of Francois and me when that photo was taken! 🙂
Firmness, Texture and Tradition
A Russian is not a pure fine meat past sausage and is, therefore, firmer than for example polony or a Vienna (which are pure fine meat past products). Here in Cape Town, a Russian which is made from fine meat past only is called a smoky or a penny polony (if it’s coloured pink). The finer a meat paste is made, the softer it is.
It has become convention to make Russians from mechanically deboned chicken meat in South Africa and many other parts of the continent. MDM is not inferior meat as many people think. It is simply chicken meat that has been removed and processed through mechanical means. (Poultry MDM: Notes on Composition and Functionality) Most large processors use micro-cutters in processing Russians and put the MDM through the process of micro-cutting also. A consequence of the production of MDM is unfortunately damage to the meat structure which results in a “softer” meat bind. Generally, how well the meat binds together after chopping depends very much on the character and quality of the starting material and if the structure of the meat is slightly damaged, micro-cutting does not help. If one puts MDM through a micro-cutter it leaves the resultant meat paste even softer. Due to this, various techniques are used to firm MDM up when producing Russians. The two most important ones are adding serials or legumes and adding meat trim or only fat. For a technical evaluation of this, I refer you to, Review of comminuted and cooked meat product properties from a sol, gel and polymer viewpoint.
There is a misconception among many that adding serials and legumes to Russians is not traditional. In my article, Origins of the South African Sausage, Called a Russian, I point out that it is the most traditional thing that can be added to the sausage and the origins of the practice come from Russia where emulsifiers and meat extenders evolved from meat stew technology which goes back millennia. In my article, Protein Functionality, the Bind Index and the Early History of Meat Extenders in America, I trace the introduction of this Russian technology into the Western world in some detail.
The legume of choice in the meat industry is soy and it is widely used as an ingredient of Russians to increase the firmness of the product. It is also convention to add either pork or beef trim with a good bit of fat to the mix which firms the product up substantially. Russians today are basically produced in the same way that it has been done for hundreds of years and it required a firmer texture than is not achieved from finely chopped meat pasts only.
“During the lockdown, I got to know the work of Petr Pakhomov from St Petersburg who is not just a Master Butcher, but an artist and one of the best exponents of the art of fine meat pasts. He opened my eyes to what is possible with Russians. I continued to study every aspect of possible ingredients in meat pasts. A concept started forming from the need to use all the natural resources at our disposal in the creation of these products. I summarised this in Nose-to-Tail and Root-to-Tip: Re-Thinking Emulsions. This made me look long and hard at all the various bits available from the carcass.
The photo on the left is of Petr Pakhomov and below is a selection of his creations. Petr famously says that he “paints with meat.”
Best Quality at Lowest Price – Invitation to Creativity
From the earliest times in South Africa, Russians were intended to be quality nutrition at the lowest possible price. Its fame was secured when it became a favourite on the Johannesburg goldfields. Inspired by concepts I saw used by Urban Foods in Nepal (Kathmandu’s Urban Food) I set out with the support of Etlin International, to develop these and create various finely comminuted meat pasts and pasts from other protein sources to be used in conjunction with MDM, meat trim, soy and starch in Russian formulations. In reality, we are building on a long tradition of making quality food affordable. I anchored most of my work in taking the concept of finely comminuting meat particles to the next level through the application of revolutionary microparticle technology, pioneered by a Cape Town company.
If a finer and smoother meat past is created with smaller meat particles, microparticles will be the next frontier. It is simply the continuation along an age-old trajectory. At first, reducing meat to small bits was done by hand. Ancient humans started to stuff small meat scraps into intestines at the kill site along with blood in order to transport it back to the tribe. For our primitive forefathers, the cost of a kill would be too great for one morsel of meat to be wasted. Cutting the meat into smaller pieces continued at the village. The earliest humans realised that reducing the meat to small meat fractions made it easier to chew. This was also in all likelihood the reason why early people started frying, roasting and cooking their meat. Ease of consumption was a huge issue to overcome!
So, at first, we finely chopped meat by hand. When the meat grinder was invented humans used a fine mincer plate to create smaller meat particles. Smaller meat particles meant a softer bite and a more versatile batter. This was followed by the invention of the bowl chopper which could reduce the meat size even further and finally micro cutters (emulsifiers) were invented to achieve an even finer particle size. A South African company pioneered technology able to create sub 50 microparticle which results in an even smoother and softer bite than was ever before possible.
A hallmark of the production of a Russian has always been creativity and making the best of raw material available at any given time and place! Turning scraps of meat into a work of art and a culinary masterpiece!
Over the 18 months, numerous friends in meat processing with factories welcomed me to run trails. Thank you to every one of you! Many I can’t mention for a variety of reasons but you know who you are! Below are photos from some of the many trails we did, each getting us a bit closer to our goal. I finally started getting traction with a few regular testing sites and when our Food Science Team started taking shape with the appointment of Dr Jess, we achieved very positive momentum. It took many frustrating months before we started working out the best way to use this technology. We ended up learning to use new technology, creating old school mixes with new technology while we were re-discovering the basics of Russian making. Our final set of trails for this round we did at PB Juicy in Maitland. Sincere thanks to Graham, Lesley, Stanford and Shelton to mention just a few along with the amazing staff who helped me on Saturday; who packed our samples and helped us prepare and participated in the tasting.
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The Easter Contest and Evaluation
Over 18 months we not only re-looked every aspect of making Russians but we also developed new ways of processing several sets of ingredients. The team was ready to put their new processes and ingredients to the test. Jess, Jan and Eben, the three parties working closest with the formulations of the new ingredients all came up with their own Russian recipes and the day before Easter 2021 we decided to put the ingredients we were working on and our own Russian formulations to the test. It was a fun way to showcase the power of our new sets of ingredients.
We each created our own Russian mix but we all included the new sets of raw materials which we developed. We used a mincer and a Kar Schnell Micro Cutter for the final cutting.
I smoked it for 40 minutes and then cooked it to an core temperature of 68 deg C.
The following day I returned for three sets of evaluation.
Pan-Fried
Braaied on an open fire
Deep-Fried in oil.
– Deep Fry Evaluation
For the Deep Fry Evaluation, we visited Marina’s Deli in Monte Vista where we were delighted to meet the Deli Owner who personally did the tasting for us. He immediately picked up that there was soy in the product and even though his clients will not buy a Russian if it is not pure meat, he personally gave us a thumbs up for both Jess and my formulations!
– Braai and Pan-Fried Evaluation
For the braai and pan-fried evaluation, we visited PB Juicy (Pty) Ltd. in Maitland, Cape Town where their amazing staff not only fried our Russians up but also assisted us in the evaluation.
– Loads of Fun and Valuable Insights
It was a huge success. Even though Jan’s recipe did not firm up as well as Eben and Jess’s recipes, we again learned bucket loads from the evaluation of all 3 Russians. Jan showed how well his formulation would work with luncheon meats and polony! Despite small differences, both the Jess and Eben formulation worked very well and I extend a hearty congratulations to Jess, my partner-in-crime for an excellent creation and to Jan for boldly going where we have not gone before! In the end, we proved the use of our new set of ingredients to reduce the production cost of Russians while maintaining a high-quality product!
Ode to the Russian Sausage
We finally come to the purpose of this post namely to celebrate the Russian! Having spent so much time with this sausage over so many months, it is only fitting to write a poem for it! 🙂 I believe all worthy endeavours in life should bring us to this point!
The Russian! What a universal delight! Melting the refined with boldness; the smooth with firmness Scraps of meat from its place of birth.; Hunger-buster in deep-Johannesburg earth!
Chopping and grinding and micro-cutting! Meat chunks and eastern legumes combining! Morsels of power from the butcher’s block Satisfying nutrition in this hard land, it unlocks!
Filling in clean casings and to the oven, it goes! Drying and smoking and drying and smoking! To cooking! Not sweating! Look, it’s firming out! In the artisan’s hand is predetermined luck!
Invented by Russians of Jewish descent! In its new African home, it is profitable appeasement! Salt and vinegar from the enemies table, Russian and chips! Feuds and animosity it disable!
Well, maybe I should continue to focus on making the product and not trying to write poetry! 🙂 🙂 🙂
I am not the only one who gets lyrical when it comes to Russians. Kobus Botes, a South African friend, living in Australia sent me this recollection after reading this post.
“I remember in the mid-to-late ’60s in Vryburg, when I was walking past the local Greek café, I bought a russian and chips to treat myself occasionally. The russian was given slits to prevent it from bursting and was deep fried with the chips and it was also given salt and vinegar together with the chips. The texture and flavour is something that is still burned into my memory. The bite started off with the oily, vinagary and salty taste, then suddenly the skin burst under the pressure of the bite. Next is a flavour and texture sensation of garlic, meat, salt, fat with a vinegar undertone. The texture was firm, with large pieces of pork fat and other large pieces of meat with a darker colour. I suspect both beef (larger pieces) and pork (finer texture) was used. Over the years I have stopped buying processed sausages at all because they all became to have a similar texture and taste. Everything is becoming like polony with modern chemicals and emulsifiers being added. Nowadays, I mostly buy imported processed meat from Italy or I make it myself. All I need is to find the authentic recipe of the russians from my childhood.”
Another South African friend from Australia, Justin (Dave) Dwyer, writes, “this certainly brings back memories of being an apprentice in the late eighties early nineties at Zululand Baconry if I had a half-cent for every Russian made I would be a very rich man. Texture is key emulsion with showpieces was the trend, then upgrading to MDM from pork skin emulsion Wow never thought I would even use those words again living in Australia, thanks for the interesting article and memories!”
A fully functional Food Science Team was created comprising of Dr Jess Goble, Marco, Helena and me to give greater impetus to these developments. Helena, Jess and myself are featured in the photo to the left at a hotel in Johannesburg where we did a product evaluation.
The team is, in reality, much wider! It also included meat professionals around the country who continue to give us advice and direction to our efforts. The feat of finally producing a sausage with a combination of old school technology and new innovations was achieved through the collective participation of every person who worked with us from around the country and includes the staff of Van Wyngaardt, Etlin’s processing facility in Durban, PB Jucy, Roy Oliver and input we received from as far afield as Nigeria. A small number of these people are in the photos below.I even include my cousin, Marius Kok who introduced me to Hungarians from Zambia.
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The Next Frontier
What we achieved over the last 18 months is only the beginning. There is still tonnes to learn! I feel like a child who has only been playing and the real discoveries and creations all lay in the future!
Some of the points on our agenda for the immediate future are:
Raw materials must be refined;
The taste profile must be further developed;
The latest innovations in ingredient technology such as modified starches, fibres, soy technology, preservation technology, etc. must be investigated and the best new sets of ingredients must be incorporated into our products and processes.
The experience we gained must be packaged and made available to the meat processing industry at large.
The role and importance of frozen meat ingredients and temperature control during processing must be elucidated and incorporated.
We are only beginning but on this Easter weekend, it is right to pause a bit and celebrate how far we have come with this project. Sincere thanks to Etienne Lotter who allows us to do this work, to my teammates both near and far, to customers who are always willing to try new ideas – a heartfelt “Thank You!”
Nitrite Free Bacon: The Quest Continues By Eben van Tonder 15 February 2021
Introduction
I started my career in meat curing in 2008 when I founded the South African bacon brand Woody’s and the company Woody’s Consumer Brands with Oscar and Anton. I never imagined that the most exciting journey on earth would follow which I chronicled in Bacon & the Art of Living. I wanted to know as much as possible about the world of curing and the chemical, biological and bacterial reactions fascinated me. One of the first books I consumed was Ronald Pegg and Fereidoon Shahidi’s work, Nitrite Curing of Meat: The N-Nitrosamine Problem and Nitrite Alternatives.
I delved into the matter with great interest. I discovered that nitrates are present in many vegetables but this is not the same as nitrites used in meat curing. The issue is not even the fact that it is far more toxic than nitrates but nitrites in products being fried and its reaction in the stomach is of particular concern. The argument that nitrites are the same as alcohol in the sense that in the high concentrations both will kill you does not hold.
What is the actual issue then and how did humans realise that there is a problem?
The Realization of Danger in the Direct Addition of Nitrites of Curing Brines and The Responses Since 1926
Nitrate was used as a curing agent for many thousands of years. The basic value initially related to the preventing of spoilage and in a world before refrigeration bacon soon became the staple meat source for the masses in a large part of the world. Curing with saltpere, the common name for nitrate salts, takes about a month and apart from retarding spoilage, it imparts into meat a characteristic pinkish/ reddish colour and a very agreeable cured meat taste. In the 1800s a new method of curing was invented which reduced the time to cure meat considerably. It was called tank curing on account of the tanks that were used to cure the meat in or mild curing due to a reduced need for salt. It was invented in Ireland. When our understanding of chemistry and bacteriology matured, we realised the reason why tank curing sped meat curing up. For curing to take place nitrate (saltpeter) must first be converted to nitrite through bacterial action before it can be changed into nitric oxide which, we discovered, is the real curing molecule. So, nitrate (saltpeter) to nitrite curtesy of microorganisms (bacteria) and nitrite to nitric oxide through is a chemical reaction.
What was achieved through tank curing was that the step of bacteria changing nitrate into nitrite is cut out. Still, we do not add the nitrite directly. It is “added” through fermentation. The old brine is re-used and in doing so, the liquid is replete with nitrite that was already converted from nitrate. This, naturally, speeds the process up by cutting a step out. Before the late 1800’s curers did not have a clue what caused curing apart from saltpeter. They arrived at the process of tank curing through experimentation and observation without any inkling to microorganisms changing nitrate to nitrite.
The curing reaction was being unraveled by scientists late in the 1800s and early in the 1900s. As we learned that going from nitrite to nitric oxide is much quicker than going from nitrate first to nitrite and then to nitric oxide. We also realized that nitrite forms a salt with sodium to create sodium nitrite. Late in the 1800s and early in the 1900s sodium nitrite was being used in the dey industry and chemists stocked it because it became an important medication to treat some blood disorders. Butchers used it as the source of nitrite. It is easier and “cleaner” than the indirect creation of nitrite through fermentation (tank curing or mild curing). Sodium nitrite can be dissolved directly in a brine and will immediately start penetrating the meat and change to nitric oxide.
Tank curing soon lost its place as the quickest way to cure meat in favour of the direct addition of nitrites to curing brines. There was an issue with nitrites though in that most people at this time knew that nitrite was a potent toxin. Understandably, from very early, humans who did not “see” the conversion of nitrate to nitrites and did not understand that nitrites were in any event present in cured meat grappled with the concept of a toxic substance being introduced in food preparations.
During the first world war, curing brines came onto the market which included nitrites. The days of tank curing were numbered and a controversy was born of how healthy this is. Several investigations were made into the matter. No sooner was the matter of the toxicity of nitrites settled through scientific investigation when another, far more dangerous issue came onto the scene in the 1970s of n-nitrosamines. Lets run through the chronology of some of the key studies and some of the important ways that governments around the world responded to it.
We pick the investigations into this matter up in 1926 which looked at the matter of nitrite as a toxin. If it was simply a matter of concentration, it would be easily settled because we regularly use substances if food which, in too high dosages can harm or even kill us. Alcohol as a very good example. The way to mitigate the risk is to determine the “safe” levels and to ensure that producers use the appropriate dosages.
1926
A 1926 study by Kerr and co-workers was based on the general knowledge of nitrite’s toxicity and the publics very negative perceptions about it. In the report, they state that public health was the primary motivation behind the study. (Kerr, et al, 1926 : 543) I quote from their report. “The first experiment involving the direct use of nitrite was formally authorized January 19, 1923, as a result of an application by one of the large establishments operating under Federal meat inspection. Before that time other requests for permission to experiment with nitrite had been received but had not been granted. The authorization for the first experiment specified that the whole process was to be conducted under the supervision of bureau inspectors and that after the curing had been completed the meat was to be held subject to laboratory examination and final judgment and would be destroyed if found to contain an excessive quantity of nitrites or if in any way it was unwholesome or unfit for food. This principle was rigidly adhered to throughout the experimental period, no meat being passed for food until its freedom from excessive nitrites had been assured, either by laboratory examination or through definite knowledge from previous examinations, that the amount of nitrite used in the process would not lead to the presence of an excessive quantity of nitrites in the meat. By “excessive” is meant a quantity of nitrite materially in excess of that which may be expected to be present in similar meats cured by the usual process.” (Kerr, et al, 1926 : 543)
“The maximum nitrite content of any part of any nitrite-cured ham [was found to be] 200 parts per million. The hams cured with nitrate in the parallel experiment showed a maximum nitrite content of 45 parts per million.” (Kerr, et al, 1926 : 543) The conclusion was that “hams and bacon could be successfully cured with sodium nitrite, and that nitrite curing need not involve the presence of as large quantities of nitrite in the product as sometimes are found in nitrate- cured meats.” (Kerr, et al, 1926 : 545)
Related to the health concerns, the report concluded the following:
“The presence of nitrites in cured meats, was already sanctioned by the authoritative interpretation of the meat inspection and pure food and drugs acts sanctioning the use of saltpeter; as shown previously, meats cured with saltpeter and sodium nitrate regularly contain nitrites. (Wiley, H, et al, 1907) (Kerr, et al, 1926 : 550)
The residual nitrites found in the nitrite-cured meats were less than are commonly present in nitrate-cured meats. The maximum quantity of nitrite found in nitrite-cured meats, in particular, was much smaller than the maximum resulting from the use of nitrate.(Kerr, et al, 1926 : 550)
The nitrite-cured meats were also free from the residual nitrate which is commonly present in nitrate-cured meats. (Kerr, et al, 1926 : 550)
On the contrary, the more accurate control of the amount of “nitrite and the elimination of the residual or unconverted nitrate are definite advantages attained by the substitution. (Kerr, et al, 1926 : 550)
Following further studies, the Bureau set the legal limit for nitrites in finished products at 200 parts per million. (Bryan, N. S. et al, 2017: 86 – 90) Conventional wisdom that surfaced in the 1920s suggested that nitrate and nitrate should continue to be used in combination in curing brines (Davidson, M. P. et al; 2005: 171) as was the case with the Irish curing method or the tank curing concept of the previous century. Nitrite gives the immediate quick cure and nitrate acts as a reservoir for future nitrite and therefore prolongs the supply of nitrite and ensures a longer curing action. This concept remained with the curing industry until the matter of N-nitrosamines came up in the 1960s and ’70s, but remarkably enough, it still persists in places like South Africa where to this day, using the two in combination is allowed for bacon. More about this later.
1931
The USDA progressed the ruling on nitrate and nitrites further in 1931 by stating that where both nitrites and nitrates are used, the limit for nitrite is 156 ppm nitrite and 1716 nitrate per 100lb of pumped, cured meat. (Bryan, N. S. et al, 2017: 86 – 90)
1960’s – N-Nitrosamine
Up to the 1960’s the limit on the ingoing level of nitrites was based on its toxicity. In the late 1950’s an incident occurred in Norway involving fish meal that would become a health scare rivaled by few in the past. 1960’s researchers noticed that domestic animals fed on a fodder containing fish meal prepared from nitrite preserved herring were dying from liver failure. Researchers identified a group of compounds called nitrosamines which formed by a chemical reaction between the naturally occurring amines in the fish and sodium nitrite. Nitrosamines are potent cancer-causing agents and their potential presence in human foods became an immediate worry. An examination of a wide variety of foods treated with nitrites revealed that nitrosamines could indeed form under certain conditions. Fried bacon, especially when “done to a crisp,” consistently showed the presence of these compounds. (Schwarcz, J) In bacon, the issue is not nitrates, but the nitrites which form N-nitrosamines.
This fundamentally sharpened the focus of the work of Kerr and co-workers of the 1920s in response to the general toxicity of nitrites to the specific issue of N-nitrosamine formation. Reviews from 1986 and 1991 reported that “90% of the more than 300 N-nitroso compounds that have been tested in animal species including higher primates causes cancer, but no known case of human cancer has ever been shown to result from exposure to N-nitroso compounds.” However, despite this, there is an overwhelming body of indirect evidence that shows that a link exists and “the presence of N-nitroso compounds in food is regarded as an etiological risk factor. It has been suggested that 35% of all cancers in humans are dietary related and this fact should not surprise us. (Pegg and Shahidi, 2000)
Studies have been done showing that children who eat more than 12 nitrite-cured hot dogs per month have an increased risk of developing childhood leukemia. The scientists responsible for the findings themselves cautioned that their findings are preliminary and that much more studies must be done. It may nevertheless be a good approach for parents to reduce their own intake of such products along with that of their children in cases where intake is high. (Pegg and Shahidi, 2000)
These studies must be balanced by the fact that an overwhelming amount of data has been emerging since the 1980’s that indicate that N-nitroso compounds are formed in the human body. What is important is that we keep on doing further research on N-nitrosamines and the possible link to cancer in humans. Not enough evidence exists to draw final conclusions.
1970 – The response to the N-Nitrosamine scare.
Back to the 1970s, so grave was the concern of the US Government about the issue that in the early 1970’s they seriously considered a total ban on the use of nitrites in foods. (Pegg and Sahidi, 2000) The response to the N-nitrosamine issue was to go back to the approach that was implemented following the work of Kerr and co-workers in 1926.
The first response was to eliminate nitrate from almost all curing applications. The reason for this is to ensure greater control over the curing. Meat processors continued to use nitrate in their curing brines from 1920 until the 1970s. One survey from 1930 reported that 54% of curers in the US still used nitrate in their curing operations. 17% used sodium nitrite and 30% used a combination of nitrate and nitrite. By 1970, 50% of meat processors still used nitrate in canned, shelf-stable. In 1974 all processors surveyed discontinued the use of nitrates in these products including in bacon, hams, canned sterile meats, and frankfurters. One of the reasons given for this change is the concern that nitrate is a precursor for N-nitrosamine formation during processing and after consumption. (Bryan, N. S. et al, 2017: 86 – 90)
The reason for the omission in bacon, in particular, is exactly the fact that the nitrates will, over time continue to be converted to nitrites which will result in continued higher levels of residual nitrites in the bacon compared to if only nitrite is used. The N-nitrosamine formation from nitrites is a reaction that can happen in the bacon during frying or in the stomach after it has been ingested. It will not happen from the more stable nitrates.
It has been discovered that nitrate continues to be present in cured meats. Just as the view that if nitrate was added, no nitrite is present in the brine as was the thinking in the time before the early and mid-1800s, in exactly the same way it is wrong to think that by adding nitrite only to meat, that no nitrate is present. “Moller (1971) found that approximately 20% of the nitrite added to a beef product was converted to nitrate within 2 hours of processing. Nitrate formation was noted during incubation before thermal processing, whereas after cooking only slight nitrate formation was detected. Upon storage, the conversion of nitrite to nitrate continued. Herring (1973) found a conspicuous level of nitrate in bacon formulated only from nitrite. As greater concentrations of nitrite were added to the belly, a higher content of nitrate was detected in the finished product. They reported that 30% of the nitrite added to bacon was converted to nitrate in less than one week and the level of nitrate continued to increase to approximately 40% of the added nitrite until about 10 weeks of storage. Moller (1974) suggested that when nitrite is added to meat, a simultaneous oxidation of nitrite to nitrate and the ferrous ion of to the ferric ion of metMb occurs.” Adding ascorbate or erythorbate plays a key role in this conversion. (Pegg and Shahidi, 2000) The issue is not the nitrate itself, but the uncontrolled curing that results from nitrate and the higher residual nitrites.
Secondly, the levels of ingoing nitrite were reduced, especially for bacon. The efficacy of these measures stems from the fact that the rate of N-nitrosamine formation depends on the square of the concentration of residual nitrites in meats and by reducing the ingoing nitrite, the residual nitrite is automatically reduced and therefore the amount of N-nitrosamines. (Pegg and Sahidi, 2000) Legal limits were updated in 1970 in response to the nitrosamine paranoia. A problem with this approach is however that no matter by how much the ingoing nitrite is reduced, the precursors of N-Nitrosamine still remain in the meat being nitrites, amines, and amino acids.
An N-nitrosamine blocking agent was introduced in the form of sodium ascorbate or erythorbate. “There are several scavengers of nitrite which aid in suppressing N-nitrosation; ascorbic acid, sodium ascorbate, and erythorbate have been the preferred compound to date. Ascorbic acid inhibits N-Nitrosamine formation by reducing to give dehydroascorbic acid and NO. Because ascorbic acid competes with amines for , N-Nitrosamine formation is reduced. Ascorbate reacts with nitrite 240 times more rapidly than ascorbic acid and is, therefore, the preferred candidate of the two. (Pegg and Sahidi, 2000)
More detailed studies identified the following factors to influence the level of N-nitrosamine formation in cured meats. Residual and ingoing nitrite levels, preprocessing procedure and conditions, smoking, method of cooking, temperature and time, lean-to-adipose tissue ratio, and the presence of catalyst and/ or inhibitors. It must be noted that in general, levels of N-nitrosamines formation have been minuscule small, in the billions of parts per million, and sporadic. The one recurring problem item remained fried bacon. In its raw state bacon is generally free from N-nitrosamines “but after high-heat frying, N-nitrosamines are found almost invariably.” One report found that “all fried bacon samples and cooked-out bacon fats analyzed” were positive for N-nitrosamines although at reduced levels from earlier studies. (Pegg and Sahidi, 2000)
Regulatory efforts since 1920 have shown a marked decrease in the level of N-nitrosamines in cured meats, even though it is still not possible to eliminate it completely. “Cassens (1995) reported a marked decrease (approx 80%) in residual nitrite levels in of US prepared cured meat products from those determined 20 years earlier; levels in current retail products were 7 mg/kg from bacon.” This and similar results have been attributed to lower nitrite addition levels and the increased use of ascorbate or erythorbate. (Pegg and Sahidi, 2000)
Despite the actions of governments and the curing industry, consumer demand has grown over the years to eliminate nitrites in food. Evidence has started to emerge that links the prevalence of colon cancer, for example, not just to the use of nitrites but to the use of saltpeter or the far less toxic cousin of nitrite called nitrate. Much of the evidence is either anecdotal or indirect but it is sufficient to fuel public suspicion and legitimate industry concerns.
What is Nitrite Free Bacon?
What is clear from our survey above is that it is a technical and complex field. When we talk about nitrite-free bacon, it is important to know exactly what we are talking about. The term can imply a number of things.
– Is the Problem Synthetic Nitrites Only (I.e. Sodium Nitrite Added Into the Brine)?
Is it that no synthesized nitrite must be used in the curing of the meat? Tank curing or fermented nitrate containing plant juices would then be an appropriate curing procedure. Celery and other plants are filled with nitrates which is part of plant nutrition, absorbed from the soil through the roots. Certain spice companies started using these plant extracts and then through a process of fermentation, allowed microorganisms to reduce the nitrite to nitrate similar to what was done in tank curing using old brine and they sold the plant extracts to be added to the meat as an ingredient. They called it a “natural curing agent” but in my opinion, they were actually deceiving the public. After the bacterial fermentation, the plant juices were now filled with nitrates. They cleverly circumvented the requirement to declare the use of nitrites in the curing process and in reality, nitrites were still present, now in usually much larger quantities as was the case using sodium nitrite.
– Is the Problem All Nitrites in the Brine and Meat, Including Either Sodium Nitrite or Nitrite that Formed Through Bacterial Action, Either through Reduction or Oxidation or Chemically and Irrespective of the Source?
Nitrite-free bacon can mean that no nitrites should be used in the curing process added directly or generated indirectly. Indirectly it can be generated through fermentation but there are other sources of nitrite which forms as a result of the decomposition of meat. In long-term curing, for example, the same colour, even a better taste and longer shelf life is achieved by the use of salt only. I mention this because it introduces a very important issue. For curing to take place, you don’t actually need nitrate or nitrite. You need nitrogen. The nitrogen must then react with oxygen to create nitric oxide (NO) which is a gas! Nitrate and nitrite are only the nitrogen source! Once Nitric Oxide is created, it must react with the meat proteins, myoglobin.
As the proteins of a dead animal or other constituents of meat are being broken down, nitrogen is made available and in long term curing, certain processes are involved and one of them is the combination of the nitrogen molecule, made available through decomposition, with an oxygen molecule and curing takes place if the overall destruction of the meat is managed through the removal of water which retards (even stops) the action of microorganisms and favours the effect of enzymes.
So, this can be done completely without any outside source of nitrogen but the process is very slow and there is no way that the world demand for cured meat will be satisfied through this. It will also be extremely expensive due to the weight loss involved in removing the moisture. No matter how you look at it, nitrogen must be accessed somehow or it is not curing.
It is extremely important to know that curing is something that happens to the meat itself and it mimics a natural, biological process of nitric oxide being formed in our bodies. The meat protein in either its oxygenated state or with a nitric oxide molecule presents red. This is an extremely important concept to understand. Curing is a characteristic of meat itself and is a natural process. It is NOT the imposition upon the meat of a colouring agent. The fact that nitrogen is used in curing is completely consistent with natural biological processes. Even the reduction and interaction of nitrate and nitrite, including the chemical reduction to nitric oxide, is a biological process, essential to life!
I give one examples from a review article by Shiva (2013). I anticipate that very soon consumers may demand food with high nitrate (NO3-) in a swing in perceptions of these molecules which will in all likelihood be driven by people who regularly work out. Shiva summarizes this work as follows. “Nitrite dependent inhibition of ccox also potentially regulates responses to physiological hypoxia (the absence of enough oxygen in the muscles), such as that present in the muscle during exercise. Larsen and colleagues recently demonstrated that ingestion of NO3- (nitrate) decreased whole-body oxygen consumption during exercise without changing maximal attainable work rate in human subjects.” Directly as a result of this work, several booster supplements are currently on the market and sold in gyms and health shops around the world containing nitrates.
Shiva continues, “This increase in exercise efficiency, which was associated with augmented plasma NO2- levels, has now been corroborated by a number of studies in various exercise models. While the underlying mechanism of this beneficial effect is not completely elucidated, a decrease in the rate of oxygen consumption due to proton leak and state 4 respiration in the skeletal muscle of subjects receiving NO3- was reported.” (Shiva, 2013)
Right there, the entire matter is resolved and in a few short years the public will demand more nitrates in meat (and by implication, nitrite also)! 🙂 🙂
Furthermore, not only is the reaction of nitrite to nitric oxide not foreign in our physiology, the reaction of nitric oxide with myoglobin is an extremely important physiological reaction that is mimicked in curing. Jens Moller and Leif Skibsted write that “Nitrosylmyoglobin (MbFeIINO), the NO complex of iron (II) myoglobin, as formed in meat products, has now also been observed in vivo in rats. MbFeIINO thus seems important in controlling radical processes associated with oxidation”. (Møller and Skibsted, 2002)
The issue is that our best available source of nitrogen is through nitrite and nitrite itself but is both beneficial and problematic at the same time.
The fact that the recation of oxygen (O2) and Nitric Oxide are both matters that all butchers work with daily is important. None of these reactions are “unnatural!” This is seen in seen in the colour of fresh meat and cured meat. I dedicated a chapter to it in Bacon & the Art of Living, called Fresh Meat Colour vs Cooked Cured Colour.
I plan to do much more work about the physiological reason why nitric oxide fits onto the colouring site of a protein apart from the short quetes above, but I will deal with this separately and update this section with a link reference.
– If the Meat itself Does Not Change Colour (Curing), is the use of External Colourant Permitted/ Desirable?
There is another way of achieving a red colour in meat which we eluded to and that is through an artificial process that involves the use of an external colourant. Legally there are colourants that are allowed in meat, but how will consumer groups respond to this? This is not something natural and inherently part of meat itself. It is an external coularant which is brought to bear upon the meat matrix. This is even more objectionable to some than nitrite and the extreme objection against it goes back to the start of the meat trade where butchers used to disguise old and sometimes putrid meat as fresh by colouring it with an external colourant.
– Is the Real Issue Actually Residual Nitrite That We Must Eliminate? (I.e., Not Ingoing Nitrite but Nitrite Left In Meat After Curing)
Another possible meaning of nitrite-free bacon refers not to the fact that nitrite was somewhere involved in the supply of the nitrogen source to form nitric oxide, but the real meaning may refer to the question if any nitrite is left in the product when the consumer fries it in the pan. It is after all not the initial source of the nitrogen atom which is the real issue, but how much nitrite is left after the meat has been cured. This is what is referred to as residue nitrite. The other question which goes hand in hand with this is to what degree can the consumer be guaranteed that no appreciable amount of nitrite is left in the product he buys?
– Is The Objective To Eliminate All Manipulation of Colour (Natural or Artificial) and Resign Ourselves to Selling Brown Bacon and Hams (uncured, salted only)?
A final solution for some is to simply omit accessing nitrogen in any shape or form altogether and not be concerned about the brownish colour that develops. I have over a few years followed the work of a New Zealand company, interestingly enough also called Woody’s who follow this approach and I am amazed at the success they have had with their brand positioning. Good old strict hygiene is used to sort shelf-life issues out and they educate their customers that the browner bacon is actually a healthier bacon. The brown bacon they sell becomes a source of comfort for their clients. If this is advisable as a universal approach to bacon or ham is debatable in a world where not everybody shares the strict attention to detail of this company, but I applaud them for their honesty and the practical way in which they have dealt with this thorny issue (see Woody’s Free Range Farm) In the end, I feel much of the problems are self-inflicted in a world where bacon flitches are no longer wrapped in cloth, palletized and shipped any longer.
By William James Topley – This image is available from Library and Archives Canada under the reproduction reference number PA-026092 and under the MIKAN ID number 3424485
How to Explain it?
As you can see from this short overview, the matter is not simple but the fact that there is an issue to address is clear. For myself, I am satisfied that in the minuscule levels that nitrite is used and remains present in bacon and hams, these products are completely safe to eat. The consumer is, however, also not wrong to be concerned about the matter. The problem is that the explanation above is already so technical – who can follow this? Let alone a dissertation by Dr. Sebranek or Dr. Møller, two of the world authorities on the subject. If anybody must understand what they are saying before one can decide which bacon is healthy and not and which brine to use or not, only a handful of people will ever make a meaningful determination on the matter. This business of reduction and oxidation, bacterial, enzymatic reactions are all very confusing for people without an advanced degree in chemistry, like myself. The only way that I could make any sense of it was to follow the story right from the beginning. As it unfolded. And what a story it turned out to be!
I will tell the story, at least the parts that are pertinent to the discussion about nitrite, from a series of articles I did on the subject over a few years and from extracts of a book I wrote about the history of bacon called Bacon & the Art of Living. These I posted on Facebook and LinkedIn earlier this year.
Before we jump into the detail, lets establish a timeline. Broadly speaking the development of bacon curing to where we are with the direct addition of nitrite to curing brine can be divided into the following timeline.
The Prehistory of Bacon Curing experimenting with various salts (sodium chloride, sal ammoniac, nitrate also called saltpeter) From antiquity to the end of the 1500s.
Saltpeter gaining popularity as it becomes widely available as a vitalizer, an ingredient in gunpowder and as medication. 1600 to 1800.
William Oake invented Tank Curing/ Mild Curing around 1832 (aged 25) – an Indirect Addition of Nitrite to Curing Brines.
Dr. Ed Polenski’s Article on Nitrite in saltpeter brines, 1891.
The academic work of German and English researchers identifying Nitrate and Nitric Oxide as the curing agents. Notwang (1892), Lehmann (1899), Kiskalt (1899), Haldane (1901).
The work of Ladislav Nachmullner and the first curing brine containing sodium nitrite (1915).
The Impact of the First and Second World War in changing the indirect use of Nitrites to the direct addition of nitrites to curing brines.
The Griffith Laboratories as evangelists of the direct addition of nitrites to curing brines. Prague Salt (1925).
“Houston, we have a problem!” The n-nitrosamine problem and the response of the curing industry and world governments, late 1950s.
The quest for Nitrite Free meat curing.
A. The Problem
A Modern Day Attempt at a Nitrite Free Brine
What sparked my review was when I looked at the curing brine offered by a Spanish company that claims that they cracked nitrite-free bacon. I am sure they did a thorough job but I did not like how they handled questions about their brine one little bit!
I decided to take the readers back to the earliest days of curing. Not just in ancient history, but when I first encountered curing salts as a small boy on a Freestate farm without even knowing it. In my web posts I wrote, “As a boy on a Free Sate Farm, we called the white sweat of horses, saltpeter. In meat curing, I learned that saltpeter is sodium or potassium nitrate. Later I discovered that it is exactly this sweat from horses which also cure meat, re-discovered by the old Boers in South Africa who hung the hunted game across the neck of the horses and, if they skinned it at the kill-site, it would start to cure on the journey back to the camp. Years of research later, I discovered that saltpeter was not our oldest curing salt. That honour goes to sal ammoniac. To test my theory about its ability to cure meat, I took one December and cured meat with it which became my first experience with an alternative curing salt. It outperformed nitrite salt in the micro department and was slightly less red than its counterpart. Over the next week, I will share my three articles that chronicle my journey of discovery! Since the time of the brilliant British physiologist and philosopher, John Scott Haldane (1860), we know that the curing molecule is Nitric Oxide. The story begins in antiquity!”
C. Nitrate (Saltpeter) Curing Spreads Around the World
An Oriental Priority
The epic story of nitrite takes us on an amazing journey: From Turfan in China, through Nepal to North India. It is one of the most riveting stories that exist. Fitting that the story of nitrite should flow through these mountains. It is a land where salt and spices abound with a depth of spirituality and taste that defies logic. The birthplace of the Buddha, it oozes with wisdom and taste. For these people, every single act is worship and every fragrance, holy! Spices hold part of the secret of finding an alternative way to prepare hams and bacon. Can it be done without nitrogen? Hmmm. . . . . There are so many “if”s that we twist reality. We have to understand why we do what we do. What is the fundamental question if we ask to replace nitrite? Do we want to shun what we perceive as unhealthy? Do we know what we ask? Are we correct in our assumptions? If we run away from, we also run towards. What? So the eternal cycles of life emerge and all arguments are settled through spices!
I not only tell the story of meat curing, but of how I first started to realise the tight link with the Turfan depression in Western China. It’s the kind of look at life that changes one’s perspective of the past completely. Through better understanding, we are getting closer and closer to a time when nitrite curing will change shape.
The Indirect Addition of Nitrite to Curing Brines: The Invention of Tank Curing
Tank curing is the indirect addition of nitrite to Curing Brines. What I mean is that we do not add nitrite to the brines. We add saltpeter which changes into nitrite over time. We add nitrites indirectly! For years the origin of tank curing eluded me till I got interested in Australia through the invention of arterial injection and interaction with my friend, Tim. One night, I was browsing through the N’th copy of old Australian documents, and whalla!!! It happened in Ireland and from there the link with Denmark unfolded like a beautiful novel! My next few posts will be dedicated to tank curing, an indirect way of adding nitrites!
Tank Curing in the Context of Bacon & the Art of Living
Even industrial bacon production is an art and the one telling the story of its history for the first time ever should do so with flair and includes all the passions of life into such an account. All this went into writing the “artistic” version of the previous post with loads more historical information. More importantly for our theme. . . . no, I still will not make the obvious applications. Figure it out for yourself! Alternatively, just enjoy the story! Oh, it is a magnificent story! So magnificent that it reminded me of Minette, my wife! It’s all in the story of the development of tank curing and instead of bacon photos I have photos of my wife because these are both passions of my life!
Dr Polenski: The Link Between Tank Curing and the Direct Addition of Nitrites
So, the world went from curing with saltpeter and salt to tank curing. After tank curing came curing with sodium nitrite by adding it directly. One monumental scientific article precipitated this change! It was an article by Dr. Polenski! No work is more pivotal! He was the first person to speculate that in curing, nitrate (salpeter) is reduced to nitrite through bacterial action. In so doing, he became the first Adamic to publish about the possible role of nitrite in curing. I have for years tried to access the only known copies of his work at three libraries around the world, to no avail. My only course of action was to travel to the libraries and access the work. However, snippet views of it were available through Google but copyright laws prohibited them from making the full article available. In 2017, I petitioned Google and asked, in the interest of research and due to the pivotal nature of the work, that they reconsider their position. They agreed and send me a copy of the full article in PDF. I wrote the following on it after I had it translated into English from High German and a meat scientist from South Africa who can read High German assisted me in working through the technical names used in his article which the translator was not familiar with. As an industry, it is one of our most valuable documents in existence!
In our consideration the history of nitrites for the purpose of thinking through the possible development of a nitrite-free bacon, we now get to one of the most interesting and important times in the development of the modern method of curing meat. Within this chapter of my book on the history of bacon curing, only in the last few weeks, I have read current publications on at least four historical considerations mentioned here, discounted at the time, which now re-emerged as likely methods of creating alternative systems of curing meat to adding sodium nitrite directly to curing brines. It reminds me of Holmes instructing Watson on the difference between seeing and observing: “You see, but you do not observe. The distinction is clear.” My challenge is the same, if you are interested in these matters, observe carefully!
The story of how sodium nitrite became the curing agent of choice is riveting! As I was reading through it again, the overwhelming sense I got was the same I had when reading again through the previous article. When considering the production of a curing brine with no nitrites, the complete and total answer is in the stories told in these two chapters along with the one before that about the curing reaction from my book on the history of bacon. It really is as simple and complex as that! And it is all there! All you need is the will to find it! Concepts dealt with here expose the charlatans and fuels the honest scientist!
After an amazing day of trials in Johannesburg with a group of great friends and the most talented research partners I’ve ever had the privilege of working with, my mind wonders to the importance of not underestimating a challenge and understanding the fundamentals of what one tries to accomplish. Nitrite Free Bacon can never be considered without understanding how curing WITH nitrites is accomplished. Here is my feeble attempt to come to grips with a complex matter.
In our quest to wonder about nitrite-free bacon, we’ve covered the important basics of curing – the reactions, the history of nitrate, the direct addition of nitrite, and the invention of tank curing. Its anti-microbial ability now becomes important, especially as it relates to C Botulinum. I wrote this article early in my journey. I later thought my views on acidification were foolish, just to discover very recently in work on fine emulsions that it was not that far-fetched. Preservative and anti-microbial options to replace nitrite have multiplied in recent years. Thoughts on nitrite as hurdle in botulinum prevention are still relevant. Much more can be said, but in the interest of proprietor information, I will leave it here. The field is fascinating and the quest achievable.
In 2015 I had the privilege to interact with Dr. R. Bruce Tompkin on the issue of the antimicrobial efficacy of nitrate and nitrite. Dr Tompkin was one of the founders of the HACCP system. We had some correspondence about the possibility to replace nitrite as a hurdle and his insights are still helpful to this day. For this, I will be eternally grateful. It was written before I discovered that tank curing came from Ireland and there are other sections where my understanding evolved. I nevertheless share it with you as I wrote it five years ago. I am thankful for experts from around the world who continue taking the time to give input not just on the matter of nitrite replaces, but on a wide array of meat and processing-related subjects. I can honestly say that if you do not know in our trade you do not want to know! (or you have been so busy that there was no time to find out!) Which I fully understand!!
So, we come to the end of our consideration of nitrite-free curing. There are numerous pathways to achieving the results and there are pros and cons to every approach! Some ingredients are so novel that only one or two labs in the world are producing the required ingredients some of which are done at costs of between $300 and $700 per g! This is not the place to review all the options. I will do this 10 years from now when I tell the story of what happened when it’s all common knowledge! The conversation I had with world experts over the past weeks not just informed me about the subject of nitrite-free bacon but the discussions permeate the work on fine emulsion sausages which is the bulk of my current focus! In the end, meat processing, as fragmented as it seems, is a wholistic discipline! I wish to thank every person who read and participated and even took the trouble to call me over the past few weeks to offer their insights. I will combine these posts into a short booklet or one page with all the different links with comments. Curing is a lifetime pursuit and a passion which I share with some of the most gifted people on earth.
The Key Figured in the Direct Addition of Nitrites to Curing Brines
If we follow the trajectory of the direct addition of nitrite to curing brine, I did a fascinating study which I re-purposed to form part of Bacon & the Art of Living, The Fathers of Meat Curing
I. The Modern Trend of Anti-Oxidants
Aloys L Tappel: A Hint of the Solution
Lets take a short break from our discovery of the history of nitrogen in meat curing. Antioxidants emerged over the past few years as an essential inclusion into curing systems. Like nitrogen, it is part of our physiology and what I love is how its inclusion mimics natural systems, like our own bodies! Curing has always done that! Developments that made it healthier ended up being closer to our physiological processes! I LOVE it!! Since the time of Tappel, we should have been able to predict its inclusion in curing systems because its inclusion in our diets is so important to our own health! In referencing antioxidants, I want to honour the contribution of this monumental scientist, Aloys L. Tappel.
In the background articles to our consideration of nitrite-free bacon, we can not skip the importance of the company structure required to bring this to the world. The relevance of what I am about to share will escape most people, but the story is interesting enough for broad consumption. The importance of corporate structure is not only confined to nitrite-free curing. It is a key consideration for any innovation to be taken to market! The most brilliant innovation, in the wrong corporate structure, will end on the shelve! Underpinning corporate structure is the availability of funds! Cash is required to drive any innovation! I am an avid hiker. We have a saying: “It’s always further. It’s always higher.” The same applies to innovation. Great innovations take more cash to get to market, not less! It’s far easier (and cheaper) launching a “me to” than something novel and will take a lot more energy than one ever imagines!
This chapter in Bacon & the Art of Living dealt with saltpeter again, but primarily with corporate structure which is my main point here. Not every company will be able to capitalize on the initial opportunities to offer nitrite-free bacon to consumers. The chapter is The Danish Cooperatives and Saltpeter
Where from Here?
I offer the following roadmap.
a. A thorough review of the latest research from around the world is required for anybody who wants to seriously tackle this issue.
b. A thorough review will have to be made related to the various functions and pathways of nitric oxide in humans, plants, and animals.
c. A review will have to be done of our current understanding of nitrosamines.
d. Antioxidants and the natural colour of fruit, spices and vegetables must be understood.
I have always been a thorough believer in a combination of old school and novel technology. All the information gleaned from the various reviews will have to be brought together and blended with old-school and novel approaches.
We must ask the very important question of which of the various definitions of nitrite-free bacon is mostly meant by the consumer. I suspect that a fair amount of confusion may exist in the minds of consumers and marketing will probably be required to “steer them to the right questions.” I am convinced that from this, a strategy will naturally develop which will in all likelihood be a combination of:
i. Scientific work – making the most productive option a reality.
ii. Education work – aligning various consumer perceptions on the most productive definition.
iii. Marketing – telling the story and endearing consumers.
Conclusion
I have no doubt in that this matter can be resolved scientifically. In terms of marketing, this can be done in a way that the consumer will be fully in-step, all the way and is taken along, not left behind or feel that half-baked ideas are thrust down his/her throat. This work is important, not just for the uncompromising drive to better and healthier food, but for the overall quest to be better in every way! To offer safe and delicious food should be the desire of every food producer on earth. Anything less both in terms of taste, quality, and safety is a crime! In this work, I can end with a quote from no finer man than Nelson Mandela who said that “what counts in life is not the mere fact that we lived. It is what difference we have made to the lives of others that will determine the significance of the life we lead!”
References
Jens K. S. Møller and Leif H. Skibsted. 2002. Nitric Oxide and Myoglobins. Chemical Reviews 2002102 (4), 1167-1178DOI: 10.1021/cr000078y
Despite the fact that I am convinced that current processing methods of hams and bacon do not pose any health rish for consumers, the demand for nitrite free bacon is not going away. Bacon and ham have always been a product for the people and whatever our personal views on the matter, the clear and growing consumer demand must be catered for.
Over the years I have seen spice companies acting with great dishonesty. They develop curing mixes that they claim accomplish meat curing without nitrites. The way they did this was by using plant extracts which are naturally replete with nitrate. Through bacterial reduction, they achieved the conversion of nitrates to nitrites which was then sold as a “natural” curing agent due to the fact that no synthetic ntirite was added. They circumvented food labeling legislation by not adding synthetic nitrite. In reality they still add nitrites to curing brines.
I have friends from around the world who build their brands on the claim that it is nitrite free and having investigated those claims, I can confidently say that they definitely add nitrites to curing of meat. It is an embarrassment just waiting to be exposed!
The Spanish Case
A Spanish producer launched a new curing system in the early part of the 2010s. They claim great results and that only plant and fruit extracts are being used. Despite this being a step in the right direction, several aspects of the development did not sit well with me, in particular the fanatical secrecy surrounding the product.
We were preparing for sausage trails today and the interview with the CEO milled through my mind. I do not understand the secrecy! Certainly there is a place for protecting proprietary information, but when the way it is being done goes against the food legislation governing all of us, it does not sit well with me. If the entire commercial viability of the approach is based upon complete secrecy, how do they expect to win the hearts and minds of the very consumers they are trying to rich out to by its nitrite-free curing brine. How will “trust me, I’m a doctor” in terms of this product be different from “trust me when I say that nitrites is not really bad for you?”
In the absence of information, people speculate and since the company is creating an enviroemt where people will speculate, let me also “speculate”. I asked the question how I would have done it if I had to copy what they did. For starters, remember that my approach is predicated on science. I have extensively looked at the curing reaction in Reaction Sequence: From nitrite (NO2-) to nitric oxide (NO) and the cooked cured colour and the colour of fresh meat in Difference between Fresh Cured and Cooked Cured Colour of Meat. There is a fundamental reason why the world works the way it works and understanding nitrite curing is intimae associated with our most fundamental understanding of the universe. In Fathers of Meat Curing I review some of the key developments.
– What they get right.
The company claims that they address Listeria spp (broad spectrum), Listeria monocytogenes, E Coli H157, and Clostridium spp (broad spectrum). The organism responsible for the existence of the meat curing industry is Clostridium Botulinum. (Clostridium Botulinum – the priority organism) and the fact they address it in their research is significant. The curing brine is effective against Clostridium Botulinum is very important. Personally I would like to know how effective it is against damaging the spore and preventing its viability. I am not sure if the study looked at that. If not, I would ask for that detail.
– Questions about antimicrobial efficacy
Challenge tests were performed where the brines efficacy was tested against sodium nitrite and compounds such as sodium nitrite plus sodium erythorbate, and a control with no antimicrobial. They claim to have demonstrated that their product performs equally well against listeria mono and Clostridium botulinum. Still, my reservations will stand.
In reviewing references to the brine, I found a claim that it its anti-microbial activity is especially effective if used with dehydrated lactic acid. Dehydrated lactic acid will itself be effective against amongst other, Listeria Monosytogenes. The one that worries me is still the efficacy against Clostridium. The claim is that its efficacy is due to traditionally processed Mediterranean fruit and spice extracts. What bothers me is that through the ages of meat processing, the producer claim that extracts were used which until now has been hidden from science. There is a lack of understanding of the experimental character of the meat curer who would, over thousands of years, if not millennia, certainly have stumbled upon these miracle substances and have incorporated it into his or her processing techniques long ago.
A further claim is made that these extracts are high in naturally occurring compounds with antimicrobial and antioxidative capacities. There are indeed a number of extracts who claim exactly this. However, what is the role of these antioxidative agents in meat curing. The context of the claims seems to point to pathogen eradication when in actual fact its role is in the prevention of fat rancidity and the development of off flavours.
– Questions about colour
The claim is made that it is these extracts are responsible for the meat flavor as well as its typical reddish color and pathogen protection, without the risk of nitrosamine formation. It is the claims about antimicrobial efficacy of the compound that is the most worrying and second to this, is the claim about the fact that it imparts a cured colour to the meat.
The most fundamental question will be this – is it causing the meat to change colour or is it imparting a colour to the meat. Is it an external colour which is imposed upon the meat or is the meat itself changing colour as it does in the case of nitrite curing?
Identifying which one it is is very simple. Let me walk you through it. For the meat to change colour, it is a reversible reaction. During curing, meat often turns brown due to oxidation, just to turn the regular pinkish/ redish colour of cured meat. It the meat is able to go from brown to pinkish/ redish, back to brown and again back to pinkish redish, you are dealing with the meat changing colour.
Secondly, look at the fat. If the fat inside the meat change colour (to pink for example), it is an external colourant applied to the meat and whether this is a plant extract or not, it must be approved as a meat colourant by the relative legislative body.
Look for an accumulation of brine. Especially in pork belly (streaky bacon) this will be noticeable where the injected brines are often trapped between the horizontal layers of fat and connective collagen. If an external colour is used, the brine pockets will display a brighter colour than in the meat surrounding it. It is one of the many reasons why it is not advisable to use a colourant in ham or bacon injection.
No plant extract without nitrogen will cause the meat itself to change colour. This is one of the laws of nature. There are colours imparted to long term cured meats which forms a purplish colour, but as far as my knowledge goes, the exact mechanism is not well understood and despite a considerable effort, scientists have not been able to replicate this effect in short cured hams and bacon.
The molecule responsible for the cured colour of meat is Nitric Oxide. Without Nitric Oxide being produced somehow by the magical concoction of spice extracts, the meat itself will not change colour and a colourant will be used. The fact that this may be a natural colourant is then a matter for consumers to decide whether they are satisfied with this, but that the meat is not “cured” in the traditional sense of the word is a fact. At best you can call it fresh and coloured meat.
– Questions about flavour
If the plant extracts impart flavour to the meat and it is not natural, does this mean that meat prepared in this way is “flavoured meat?”
For starters it would have been very easy if one used nitrates. I see no mention of it in their literature. If I had to guess how the cure is made, I would say they possibly could be using reduced amount of nitrates but my guess would be that if this is used, residue nitrites are disposed of during the curing process. How to convert the nitrate quickly to nitrite would have been the challenge. I would have used techniques developed through the celery and beetroot juice developments where nitrates in plant extracts were converted to nitrite. In salami manufacturing, the use of starter cultures have become so commonplace that it will be easy to impregnate the brine with bacterial cultures who can achieve the conversion quickly. I would have elevated the levels of ascorbic acid, to ensure that nitrites are rapidly converted to nitric oxide which achieves the cure. I would add plant extracts to bolster the reduction to NO, to add flavour, to assist in the colour and to confuse the issue. Paprika, red chili’s, red pepper, etc are good colour enhancers especially for a darker, reddish colour. In terms of micro I would rely on nitrite, nitrate and the anti microbial action of the plant extracts which I would add. I would set out a tight schedule in terms of how long the product must be cured before the important test is done for nitrites.
From correspondence with the company, I learned that they say that the meat itself does not change colour which means that they are not using nitrate, but in the absence of full disclosure, how do we know? Who says that the statement is not purposefully vague? However, lets take them at their word. Lets assume that nitrates are not used. Like them, I would reply on plant extracts.
Supporting Correspondence
Remember that I have no knowledge if this is actually how the curing brine is being made. I discovered one bit of information that I can use to get some idea if I am on the right track or not.
I looked at mail communication that was made public related to the product under the access to information law. In this communication, regulators are asking questions which I echo.
The company has to make known the materials used (more detail than edible spice and fruit extracts) and if they claim that the meat colour is changed itself, show how by which mechanism this is achieved. Failing which, it is an external colourant and must comply with colouring legislation. Failing such disclosure is against the letter and spirit of our food laws. (Refer to my article Concerning Chemical Synthesis and Food Additives)
The question is asked as to “what kind of processes are being used e.g. physical, chemical or microbiological for the extracts? How many steps are there in the extraction process?”
Another good question that came up was for a “simple flowchart”. The company claimed, I assume, that “simple ethanol water extraction, using traditional methods of extraction and no selective physical or chemical extraction of constituents” are used. The legislature ask for “further detail, for example, is the extract a standardized product? How do you prevent variation?” These questions would be asked from us who use the product in processing and the company has to comply.
The all important question is then asked related to the “active component or components that are being used as a substitute for nitrite/nitrate preservatives to prevent the growth of harmful microorganisms and/or increase shelf-life? If this is considered commercially sensitive information can you describe how it kills or prevents the growth of microorganisms? These are the same questions I have raised above. Meat science is not an isolated discipline being pursued in dark corners any longer. It is done at almost every university and high profile meat institutes and if another product was available for curing meat apart from nitric oxide, television programs would have been made about the discovery and every scientist on earth would have known about it.
Related to the colour of the meat, it seems as if the company stated that the meat does not actually change colour. The legislator asks, “Does any component impart a colour change in the pork meat?” The statement is then made that the company has said that “no component used imparts a colour change in the pork meat.” This being the case, the follow up question is then “Does any component prevent colour change?”
In terms of flavour, using the plant extracts will certainly qualify the products as flavoured bacon? How does the plant extracts not impart their flavour to the meat and how is the flavouring natural?
A Better Way
I am of the opinion that the use of pant extracts is warranted. I am working on a completely new direction that may or may not include plant extracts. Even if I opt for plant extracts, I have an ongoing problem with current extraction processes and prefer the products to be used in the form in which it is found in nature. The discussion from the legislator with the Spanish company bears this preference up. Resent equipment developments make a better raw material possible. Another key lesson to learn from the Spanish example is the importance of taking the consumer and industry along in the process. A man walking too far ahead of the people he is trying to lead is a man out for a walk and not a leader. He will achieve nothing! Bacon and ham and health – they all belong to all of us!
Meat-on-Meat Bacon and Ham: Injection for Profit and Taste Eben van Tonder December 2020
Introduction
After many years in the bacon industry, and working on sausage technology, I was able to conceptualise a complete bacon line, almost fully automated, exploiting a selection of different equipment and sets of technoligy, and in cooperation with a few key players in the industry, to design a bacon line which will deliver volume, at a cost never achieved before.
The new technology will, for example, make vastly reduced nitrite and possibly nitrite free bacon a reality which is not based on smoking-mirrors, as is currently wide spread in offerings to consumers. Plant based brines are used where nitrites are produced by the plants in large concentrations due to how the plants are cultivated and by exploiting loopholes in legislagion, producers are not declaring the nitrites since they did not add chemical nitrites. They only declare the plant juices but do not have to say that by adding these, the also added extraordinary additional quantities of nitrites.
New technology we are working with makes it possible to produce bacon with either very low nitrite levels or, possibly even, removing it completely. (Removal of Nitrite from Meat Curing Systems)
The fact that the system we are conceptualising is continus with minimal handling becomes a powerful hurdle against clostridium and botulinum poisoning which is the reason why nitrites is allowed in meat.
The main contribution I want to focus on here is, however, the possibility for meat-on-meat injection with a scope of application that has not been possible before. Further, I want to put it in the context of the best bacon system on earth since it is only one additional building block to a complete system.
Much of the thinking was inspired by sausage technology.
From Sausage Technology – Back to Bacon
I have been working most of 2020 on fine meat emulsions (Nose-to-Tail and Root-to-Tip: Re-Thinking Emulsions). Most of my work was on re-working the formulation. I started by grouping the different chemical reactions together along with ingredients which links to the reactions. From this I produce a number of emulsions (emulsions is an old and incorrect industry term – meat paste is more accurate). The different pastes are created seperate using the new super emulsification system. The different pastes are then combined through a mixing step, where spices and showpieces are also added. It was during this phase of trails, creating the different meat pasts, when I bacame aware of the possibility to apply the technology to reduced nitrite or even nitrite free curing systems.
After blending, we move to filling through a filler and a hanging line into a continuous smoking system. No trollys required. The sausages goes in on the one end, are dried, smoked and schillied in one continuas system and comes out on the other end at 4 deg C and packed immediately. It easily adds another hour production time, reduce staff cost and handling and improves product quality, consistency and safety! On the back end, we are looking at continuous and automated packing solution and a man who designed and implemented one of the largest of these lines in the world will be assisting me.
The Relevance to Bacon
I started my career in meat processing as a bacon man and as I was working today, I thought about BACON! The applications of what I learned this year are enormous.
Meat-on-Meat Injection, through the use of the super emulsifier, becomes the most obvious application in brine injection. Inject lower cost trim with spices added into whole meat muscles. Around the world, super quality meats are produced using the general concept of injecting meat into meat. It has, however, never been this easy or commercially viable! The list of possible raw materials used for such injection is also tremendously expanded.
In formulating the brine, we are able to use components such as tendon and rinds which for the first time is now injectable! Other systems exist, but not one as simple, clean and wide in application as this one.
Below I introduce you to the equipment which will produce the brine. This innovation may very well be the biggest breakthrough in brine technology over the past 100 years since the direct addition of nitrites to curing brines. (Best Bacon and Rib System on Earth)
Meat-on-Meat
We can now continue to place the new technology in the context of the broader bacon system.
The injected bacon logs are rested and loaded into bacon grids which we designed (Best Bacon and Rib System on Earth). We opted for individual baskets which are filled and pressed individually after which the entire log with the basket can be loaded into the smoking/ cooking/ freezing chamber. It will be easy to see how it works if you study the baskets and the pressing system shown in Best Bacon and Rib System on Earth. The fact that the baskets are ONLY removed at the end of the line, after freezing, speeds the smoking and freezing process up due to the effect of the stainless steel and its thermal properties.
The same approach to the continues drying, smoking, cooling of the sausages has been adapted with a freezing step at the back. It is envisaged that bacon logs will be de-gritted at slicing temperatures or slightly above if manual Treif-type slicers are used. An automated de-grid system is being designed that must allow the grids to slide into the system which removes the lid from the basket, tips the basket over for the bacon log to fall out from where it moves directly to the slicer or, alternatively, to a boxing station where they are boxed and palletised before storage in a freezer for later slicing.
The basket are then either sent to the manual cleaning station or into an automated high pressure spray cleaning system.
Slicing/ packing solutions have been developed over the years which makes automated slicing and packing possible with minimal human handling. Several very good system is available commercially.
Pasteurisation?
The one major issue I don’t have clarity on is Pasteurisation. High-Pressure Pasteurisation, for all its claims, does not seem to add up to a viable investment compared to heating systems (PPP) which can be constructed in-house or at much lower cost by contractors. This is the consensus opinion of production managers from around the world whom I consulted on the matter. I have had no time to look in more detail into the matter myself. The fact is that some form of eliminating contamination during packing should be part of the total system. The effectiveness vs total cost of ownership of the different systems must be thoroughly understood. Systems working with light and ultrasound should also be considered and combination systems. I would love to receive comments and input on this matter especially from production managers. In South Africa, there seems to be a wholesale rush to HPP, but I am not convinced. It may be, but I would love to see the data for myself and get more input from production managers and business owners with first hand experience.
Conclusion
I feature new technology in terms of brine preparation, but set out new thinking about drying, smoking, chilling and freezing through one of the most advanced Smokehouse producers in Europe. We developed a bacon grid system which fully integrates into this drying, smoking, chilling and freezing system and skilled designers are completing the work by focussing on an automated offloading and de-gritting system from where the bacon will either be sliced or stored.
The possibility exist to use the new brine preparation technology featured here, to create vastly reduces nitrite or even, possibly, nitrite free curing systems.
All-in-all, claiming that this is the most advanced system on earth is not an exaggeration!
Origins of the South African Sausage, Called a Russian Eben van Tonder November 2020 (Cape Town) (Updated 22 October 2023, Lagos, Nigeria)
Introduction
I have long tried to reconstruct the history of the South African sausage delicacy called a Russian. Due to a complete lack of information, I never did. Earlier this month I decided to give it another go as an introduction to a groundbreaking article by Dr RA LaBudde on fine emulsion sausages. (Review of comminuted and cooked meat product properties from a sol, gel and polymer viewpoint) I posted a short essay on social media and immediately started receiving high-quality input.
The Russian Connection
Is the name – Russian, a reference to a Russian origin? In its composition, it is similar to the Russian Kolbasa. The Russian word kolbasa, as well as its variations in the Slavic languages (for, example kielbasa in Polish), originated in what is now Turkey. It literally means “pressed by the hand.” (Though some researchers stick to the Hebrew origin of the word – the word combination kol basar used to mean “all flesh”.)” (Russiapedia) In Slovenia, it is called a kransky and the Poles, kielbasa.
Early Russian Immigrants
One option is that it is Russians who brought it to our shores. Most Russian immigrants, were, however, Jewish and since the product in South Africa contains pork, I was sceptical.
In early Johannesburg, a large Russian community dominated the grocery trade. Cripps (2012) quotes a 1905 complaint from the Commercial and Industrial Transvaal which read: “Perhaps in no branch has the keen edge of competition reduced the retailers’ margin of profit to such a minimum as in the grocery line. This is due in a great measure to the number of Celestials, Greeks and Russians who have got a hold of the Transvaal trade, and whose nominal expenses and cost of living enable them to curtail the ordinary profits.”
Cripps (2012) writes that “the 1896 Census showed a total of 102,078 inhabitants in Johannesburg… Of these 50,907 were Europeans or whites, 952 Malays, 11 4,807 Asiatics, 12 2,879 mixed or other races, and 42,533 ‘natives.” Of the 24,489 whites who had been born in Europe, 12,389 were from England and Wales, 3,335 “ Russia, 2,879 “ Scotland, 2,262 “ Germany, 997 “ Ireland, 819 “ Holland, 402 “ France, 311 “ Sweden & Norway, 206 “ Italy, 139 “ Switzerland and 750 Others. (Cripps, 2012) Apart from a direct reference to their involvement in dominating the grocery trade, it also means that Russians were the second largest group of white foreigners in Johannesburg.
Cripps (2012) shows how each nationality was eager to develop and sell their traditional food and even though she does not mention Russians (the sausage), one can be certain that Russian immigrants sold their sausages, kolbasa or another variety, to the general public.
An Anglo-Boer War Russian Connection?
We know that Russians fought in the ABW on the side of the Boers. Could they have brought the tradition over? Leaving the exact definition of who these Russians would have been aside for a moment, one wonders where they got the equipment to produce it but at that time, people were capable of producing complex meat formulations in their kitchen before breakfast (as is still the case in rural households across Russia, East and Central Europe). Several prominent ethnic Russians joined the Russian effort and it could have been produced for them during the campaign under instruction by wealthy fellow Russians.
Davidson and Filatova, in their book, The Russians and the Anglo-Boer War, 1899-1902, mention several such high-ranking Russian aristocrats and leaders who participated in the war. One such person was the Georgian Prince Nikolai Bagration, a descendant of Marshal Bagration who had fought against Napoleon, who was a well-connected aristocrat who once represented Georgia at the Tsar’s coronation. He was nicknamed, Niko the Boer. Others were people like Prince Mikhail Yengalychev, Ivan Zabolotny and Alexander Essen. “Zabolotny became a leader of the Trudoviks and a member of the First Duma. Essen was already a member of the Social Democrats when he arrived in Pretoria and was to play an active role in the 1905 Revolution – his underground alias was ‘the Boer’. He went on to become a leading Bolshevik and in the Twenties was appointed deputy chairman of the Russian State Planning Committee.” (quoted from an online review of Davidson and Filatova)
A few hundred Russian volunteers participated, and it is likely that they prepared Kolbasa for their own consumption and even for Boer commandos whom they fought alongside. In further support of the possibility that they produced during the campaign, there is photographic evidence of meat grinders being available and used in the field by the British and therefore possibly the Russians (see under “Meat of War” in The Boers (Our Lives and Wars). If the Russians shared their kolbasa with the Boers, it would have cemented the reputation of the Russian sausage and would have endured it to the Boers.
Hans de Kramer, however, correctly pointed out that “very few of the 200 or so Russians who fought with the Boers in the ABW came directly from Russia. They were Jewish rather than ethnic Russians who had come to the ZAR by the thousands since the middle of the 1890s. In the Boer War, the neutral Russians (they were mainly neutral but about 3000 joined the British army) suffered with the Boers during the British scorched earth phase because many of their shops were on farmland owned by Boers and their shops were burned down because they were suspected of supplying the Boers during the guerilla phase. After the war the Russian Jewish shopkeepers claimed compensation from the British for burning down their shops, saying that they did not supply the Boers but that the Boers just arrived at their shops and commandeered food and other goods which they supplied out of fear. They described themselves as general dealers and storekeepers who were dairymen, BUTCHERS, tailors, hawkers, booksellers, a blacksmith, a printer, a hairdresser and a handful of farmers.” It seems that the numbers of Russians were so small that one wonders if they had a particular effect during the war on the creation of such a culinary tradition.
Could the Original Sausage have been Kishka?
It is clear that there were not enough ethnic Russians in South Africa for the original sausage to have been Kalbasa (assuming that Kalbasa always contained pork). If the original sausage was Kishka and not Kilbasa, everything would fit because we know that Kishka is a well-known Jewish sausage, containing offal. Kishke is Slavic in origin and means “gut” or intestines. This is also made across Eastern Europe and every country calls it by its own unique name.
There is a strong tie between a Kalbasa and a Jewish origin as we saw from the origins of the word. “Some researchers stick to the Hebrew origin of the word – the word combination kol basar used to mean “all flesh”) (Russiapedia) There are historical records of Kosher butchers making Kalbasa.
The Russian is not just like the Kolbasa, but also other Central and East European sausages. The Australian, Vic Nicholas, with his strong South African ties, pointed out that the South African Russian is very similar to the Slovenian Kransky (Krainer in German). East European and Russian peoples all made a similar, very basic sausage referred to by various names. A similar sausage is found in Germany, Slovenia, Hungary, Poland and Slovenia’s neighbour, Croatia who probably took their version of the same basic sausage to Australia where it is called a Kransky. Different peoples, therefore, made a similar sausage and called it by different names and it would be natural for the Jewish butchers to have done the same and simply omitted the non-Kosher components such as the blood and pork.
Kishka or kishke remains a good contender. For starters, I know that Russians are very similar to polony in terms of its ingredients and polony definitely included offal in its initial recipe (The Origins of Polony). Kishke is a sausage stuffed with intestines and made from a combination of meat and grain. The fact that it contained grain, often soy, makes Kishka very similar to a South African Russian than most people may realise, as the traditional South African sausage contains a combination of meat and soy. What grain would have been used in Johannesburg in those early days to add to the sausage is an interesting question as soy only became popular following WW2. That it contains both meat and grain or legumes today is certain. Even if it did contain legumes early on in South Africa, the fact that it does so today has more to do with the economic imperative to make expensive meat affordable than any historical reason. If grain was used earlier with the meat, it would have “opened the door”, so to speak for a later inclusion of soy.
Jewish-Russian Immigrants
Even though I could not find any reference to the Russian sausage and its consumption during the Anglo-Boer war or on the mines in the Transvaal, Hans de Kramer claims to have “seen a source stating that the Boers developed a taste for Russian sausages through obtaining them from the Jewish Russians during the ABWII.” Most interestingly, he also states that “Russian sausages were popular in Johannesburg amongst the very cosmopolitan mining community since a decade before ABWII.” I have learned to trust statements like these on cultural matters where there would be no reason one way or the other to embellish and I take Hans completely at his word. This is, after all, the nature of recording tradition.
Jewish Russian shopkeepers stocked Russian sausages and sold them to the Boers during the ABW and on the Johannesburg Reef to the mine camps. The existence of these camps was at the heart of the development of an enormous meat trade in Johannesburg.
Reaching Far and Wide
Not just the Russians, but the people from the Balkans and Eastern Europe (such as Germany, Slovenia, Hungary, Poland and Slovenians) specialised in it and it was the Russians and East Europeans who brought this technology to America following World War One. There are records in Russia of even kolbasa being produced with fillers and extenders due to meat shortages in Russia (Russiaperia).
People from the Russian steppe and surrounding regions pioneered the use of meat extenders and supplements as emulsifiers and fillers which probably developed from their millennia-old soup technology. Fine emulsion sausages became important in America, after the war during severe meat shortages. In central Africa, the same sausage sold in South Africa as a Russian is called a Hungarian after the people who brought them the technology. They produce it minus the showpieces, but omitting these may be a later adaptation. see my article on this subject, “Protein Functionality, the Bind Index and the Early History of Meat Extenders in America.”
In 2023, two papers I did had a huge impact on my thinking about the Russian sausages. One is “The Gluckman Project” where I trace the immigration from Lithuania to South Africa of the brothers Maurice and Nathan Gluckman and the other is the creation of a Jewish newspaper in Johannesburg, also by a Lithuanian immigrant, Ben-Zion S. Hersch, “The Jewish Standard.” This importantly introduced me to the largest of all Russian groups to have ever immigrated to South Africa namely Lithuanian Jews.
Lithuania was for some time part of the Russian Empire. Russian domination of Lithuania goes back to the 1700s. The Third Partition of Poland, also known as the Third Partition of the Polish-Lithuanian Commonwealth, took place in 1795. As a result of this partition, the territory of Lithuania, along with much of the Polish-Lithuanian Commonwealth, was divided among Russia, Prussia, and Austria. The eastern part of Lithuania, including Vilnius, came under Russian control.
Lithuania remained under Russian control for over a century, during which it was part of the Russian Empire. On February 16, 1918, Lithuania declared its independence from Russia and established the Republic of Lithuania. This declaration marked the end of its formal association with the Russian Empire. It is therefore likely that the sausage was introduced by Lithuanian Jews (or one of the other Jewish ethnic groups from under the Russian Empire) and that the immigrants were generally referred to as “Russians”.
There is a major flaw with this theory namely that during the period when Lithuania was part of the Russian Empire (1795-1918), the Lithuanian population was generally not referred to as “Russians” by the outside world. The people of Lithuania, including ethnic Lithuanians, retained their distinct cultural and national identities, despite being subjects of the Russian Empire. This was true of other countries incorporated in the Russian empire.
It did, however, give me a specific direction to search for the sausage. Amongst Lithuanian Sausage I discovered an excellent contender called a Kiełbasa Litewska. It has all the main ingredients for a Russian including showpieces. I will give the following recipe I found on Meat and Sausages.
Ground allspice berries are allspice, but a mix often includes cinnamon, cloves, nutmeg and ginger. In South Africa, we will add cardamon, cumin, marjoram and onion powder.
How the sausage is made is the interesting bit. Notice the use of fat as “show pieces.” This is exactly how a Russian sausage is made in South Africa.
– Instructions
Grind pork with 3/8” (8 mm) plate. Grind fat trimmings with 3/8” (8 mm) plate. Grind beef with 1/8” (3 mm) plate. Grind meat trimmings with 1/8” (3 mm) plate.
Emulsify ground beef and meat trimmings adding 20% (120 ml, 4 oz fl) crushed ice or cold water. Add salt, cure and spices during this step.
Mix ground pork, ground fat and emulsified meats together.
Stuff into 32 mm hog casings. Form 25-28 cm (10-11”) links and divide into pairs.
Hang for 12 hours at 2-6° C (35-43° F) OR for 1-2 hours at room temperature.
Apply hot smoke at 55-60° C (130-140° F) for 80-100 min until light brown color is obtained.
Cook sausages: in water at 72-75° C (161-167° F) for 25-35 min until meat reaches 68-70° C (154-158° F) internal temperature.
Cool in water. Refrigerate.
OR: bake in smokehouse. In the last stage of smoking increase temperature to 75-90° C (167-194° F) for about 30 minutes until sausages reach 68-70° C (154-158° F) internal temperature. Cool in air to 18°C (64°F) or lower. Refrigerate.
To make a semi-dry sausages add the following steps: sausages cooked in water are submitted to a secondary smoking: with cold smoke (18° C, 64° F) for 12 hours OR with warm smoke (24-32°C, 75-90° F) for 6 hours.
Dry sausages (baked or cooked) at 12-18°C (53-64°F), 75-80% humidity for 2-3 days until sample sausages achieve 86% yield. If mold appears wipe it off.
Notes: *meat trimmings: hearts, tongues, beef head meat, pork head meat. (From Meat and Sausages)
As a contender for the Russian sausage as we know it in South Africa, Kishka or kishke may have influenced it, but the inclusion of serials and grains before soy isolated proteins were available would have given the sausage a “mushy” texture as less protein meant less gel formation and less hardness. The Lithuanian Kiełbasa Litewska is a far better contender with nice firmness and a snap (Knakt) when it is bitten into or bent over till it breaks. In this regard, there is little difference between the Polish Kielbasa and the Lithuanian Kiełbasa Litewska. The main differences relate to the spices used.
An excellent article appears in Taste of Artisan. Victor, the creator of the website did an amazing job of giving the background to a smoked version of the Kielbasa, the Kielbasa Lisiecka which is, what the Lithuanian sausage will look like related to texture and show pieces.
We have not answered two key questions. One relates to the use of pork for a sausage sold by Jewish shopkeepers and clarity relates to the name, a russian! Let’s first consider pork.
Why Pork?
It is easy to say that pork was cheaper than beef (as was and is the case) in South Africa and that the Jewish shopkeepers put their religious objections aside in favour of monetary gain. A notable example of a prominent Orthodox Jew in the pork trade was none other than Aron Vecht was arguably the largest meat curer to have existed. I have written extensively about him. From my book on meat curing, Bacon & the Art of Living:
The problem with this view is that of all the places on earth where the strictest interpretation of the religious documents of the Jewish faith was applied, Lithuania was right at the top of this list. I cannot imagine that they would have set gain before principal. Money above faith was never an option!
A British author recently pointed out to me that a kosher butcher producing pork products was frowned upon in the Jewish community. Apparently, it was frowned upon but allowed if the Jewish butcher did his pork production from a different factory/ site. Vecht would fall in this category as he had dedicated pork production sites around the globe.
In terms of structure, this discussion may get us closer to Kielbasa as the original inspiration, but still, the name is an enigma.
Related to the Name: An Intriguing Suggestion
While I was researching the Lithuanian Jewish population, the development of Zionism, and the immigration of the Gluckman brothers and Hersch to South Africa, a thought occurred. It would warrant a separate article, but I summarise the result of my investigation here.
One of the key driving forces behind the development of Zionism was the persecution of the Jews. In the entire world, in the 1800s and early 1900s there was probably no place where anti-Semitism was more severe and led to more misery at an unimaginable scale as in the Russian Empire. I wonder if the creative Lithuanians and other Jewish immigrants (actually, refugees) from the Russian Empire, when they had to come up with a name for their sausages, originally made from offal and meat scraps did not think that “Russian” was an appropriate name for the sausage to deride, express contempt and scorn towards the Russians.
This could even cover the inclusion of pork in this dish. We know that the name, “Russian” in all likelihood does not refer to the country where the sausages originated. Why not call it a Lithuanian or a Polish? This is, however, exactly my point. Contained in the russian sausage may be the story of the Jewish people and how they were treated around the world for millennia and in the Russian Empire in particular.
Today, in South Africa, Russians are made from the best quality meat and linking any nation to the sausage would be something to be proud of, but back then it was the intestines and meat scraps. The historical context opens an interesting possibility.
A point must be made about the almost complete silence from history related to the naming of the sausage. Despite extensive searches I have made myself and professional researchers, we can find almost no information to shed light on the topic in the historical records. This is not unheard of, but the silence is enough to strike one as odd. If what I propose here is true, it would explain why nobody was prepared to put pen to paper and write this down. Even more, if it were produced with pork, even from a different factory, it would make sense why nobody was talking about it and telling the story.
Best Not To Be Dogmatic
It is the Russian Mater Butcher and acclaimed chef, Petr Pakhomov, who taught me not to be too dogmatic when it comes to sausage recipes. Different regions and countries used their own creativity to give their own interpretation of the sausage and used as ingredients whatever was available and allowed in their community to be used. Petr is a great example of a man who continues to re-interpret tradition by coming up with new and creative ideas all the time. (Review of comminuted and cooked meat product properties from a sol, gel and polymer viewpoint)
Conclusion
The original sausage in South Africa, introduced by Russian immigrants, almost exclusively Jewish, could even back then have been made with soy and other gains included as was the tradition at some point in history. It certainly is the case today. The most widely used recipe in South Africa today contains almost exclusively chicken, pork or beef trim, some soy and a bit of starch, filled into either a hog casing or into a sheep or beef casing if religious rules preclude the use of pork. Some butchers may add some cooked pork rind to give flavour and body. It is always cooked by the butcher to at least 69 deg C and most butchers smoke it. In recent years, some butchers have opted for beef collagen casings but this remains challenging when you deep fry the Russian as is often done.
Russians Sausages – its history, naming and composition are remarkable!
Dr RA LaBudde does a great treatment of fine emulsions. There are of course many other excellent works on the subject but the language LaBudde used, I can understand!
I give the work of Dr LaBudde on the subject here in its entirety. It is important to remember that this is only one half of the equation. Meat processing is an art as much as it is a science. For the “art” we will feature the work of the Master Butcher from Saint Petersburg, from Russia, who gave the world fine meat emulsions, Petr Pakhomov.
The fact that we call the most famous fine emulsion sausage in South Africa, a Russian, comes from its Russian origin and was either introduced to South Africa by early immigrants or, more likely, by Russian volunteer who fought on the side of the Boers in the Anglo Boer War. Not just the Russians, but the people from the Balkans and Eastern Europe specialised in this and it was the Russians and East Europeans who brought this technology to America following World War One. People from the Russian steppe and surrounding regions pioneered the use of meat extenders and emulsifiers and fillers which probably developed from their milennia old soup technology. Fine emulsion sausages became important in America, after the war during sivere meat shortages. In central Africa the same sausage sold in South Africa as a Russian is called an Hungarian after the people who brough them the technology and traded it across the region. They produce it minus the showpieces and omitting these may be a later adaptation.
Petr Pakhomov is not just a Master Butcher, he is an artist and one of the best exponents of the art of fine meat emulsion. In a 2020 book he published on the subject, he writes: “This publication includes recipes for sausages from offal – an undervalued and rarely used raw material by sausages. On the counters of butcher shops there are hearts, liver, tongues – only these offal are well known to the townspeople and are in demand with them. The rumen, kidneys, brains, lungs, udders, properly prepared and cooked, are sometimes a discovery for people far from rural life. By-products allow you to create unusual in texture, very tasty, with a beautiful pattern on the cut, brawn, jellied, pate. A readily available and easy-to-use raw material is poultry meat. It serves as an excellent base for sausages and sausages, allowing you to play with taste thanks to the addition of various spice mixtures. The pale pink minced meat is a great backdrop for unusual cut patterns.”
“Of course, I have not ignored pork and beef products. My credo can be expressed by the words: “I paint with meat!” To make the sausage original, standing out on the counter among the usual – this task fascinates me. The appearance of the sausage product, the drawing on the cut should catch the eye of the buyer. Then comes the turn of consistency and taste, a successful combination of textures and spices.”
In this Petr strikes every single cord close to my hear and so, in celebration of his art and the science of Dr LaBudde I feature Petr’s work throughout the work of Dr LaBudde.
Abstract
Comminuted and cooked meat products are viewed as water-plasticized, filled cell mixed-composite thermosetting plastic bio-polymer. This theoretical model is used to explain many factors influencing finished product quality attributes and to conjecture possible interactions between materials used in formulation. The relation between product texture and “bind” and “gel-strength” is described.
CONTENTS
Introduction
Meat Process Control Concepts
Meat Product Non-Chemical Properties
Meat as a Polymer System
Testing General Polymer Strength
Testing Meat Product Gel Strength Properties
Effects of Materials and Processing on Gel Strength
Skin vs Bulk Strength
Sensory Properties Influenced by Gel Strength
Typical Lot-to-Lot Variation in a Frankfurter’s Texture
Exhibit 1: Process Control Logic Exhibit 2: Force-Deformation Curve for Brittle Plastics Exhibit 3: Force-Deformation Curve for Ductile Rubbers Exhibit 4: Stress-Strain Relationship for Meats Exhibit 5: Typical Lot-to-Lot Variation in Stress for a Frank
Appendix 1: Glossary Appendix 2: Bibliography
1.0 INTRODUCTION
Comminuted meat products include a wide range of consumable sausages: frankfurters, bologna, luncheon meats, smoked sausage, bratwursts, fresh sausage, ground meat, dry sausages and many others. We shall be principally concerned with cooked sausage which is intended to be bound together with some degree of strength in its manufacture. This is not intended to mean that this discussion is limited in applicability to these types of products, or even meat products in general, but to provide an example set of products for which the concepts described provide critical insight.
Most of the time we will be even more specific: the most frequent product examples used will be a frankfurter (cooked, fine-cut, eaten hot), a bologna (cooked, fine-cut, eaten cold) and a smoked sausage (cooked, ground, eaten hot). These particular products are sensitive to consumer perception of texture, represent a large volume of North American production and exemplify broad ranges of product categories.
Cooked sausage production of the frankfurter, bologna or smoked sausage types occurs in the following sequence of typical steps:
The raw meats to be used are first ground to medium fineness. For lean meats (< 30% fat) this means to 3/16″ (5 mm) and for fat meats (> 30% fat) to 3/8″ (10 mm) or larger.
The bulk of the meats used, together with 15% water and 2.5% salt and possibly sodium nitrite, are mixed together for 5 to 15 minutes at slow speed and dumped into vats.
The “preblended” meats of Step 2 are left to age for 8 to 24 hours.
A “final blend” is performed by mixing the “preblend” plus additional water together with sweeteners, spices and flavorings for 3 to 5 minutes.
The “final blend” is dumped into an emulsification mill(s) or a fine grinder (< 1/8″ or 3mm).
The fine-cut meat batter is stuffed into casings.
The stuffed product is showered with liquid smoke and 2 – 4 % acetic acid.
The product is cooked in a humidity and temperature controlled oven. A typical cook schedule might be: 30 min. @ 130 F (54 C), 30 min. @ 190 F (88 C). The humidity is low in the first stage, allowing the product to “shrink” and form a “skin”. The second stage will have a controlled humidity of at least 40% to promote rapid heat transfer. The product center temperature will be 160 to 170 F (71 to 77 C) leaving the oven.
The cooked product is showered with cold water or brine for 15 to 30 minutes to bring its temperature to 35 F (2 C).
The casings, if inedible, are removed by slitting and peeling.
The product is packaged under vacuum or modified atmosphere. Cooked meat products are composed of a variety of basic substances: moisture, fat and protein (comprising some 94% of the weight), salts (2 – 3%) and carbohydrates (3 – 4%). The carbohydrates include starches, sugars and fiber. These constituents are the real raw materials used in making meat products: the raw meats are simply variable “preblends” of moisture, fat, protein, etc.
2.0 MEAT PROCESS CONTROL CONCEPTS
Process control is composed of five basic steps (see Exhibit 1): 1) Measurement, 2) Standards or Targets, 3) Comparison of Measured to Standards, 4) Plan of Action, and 5) Implementation of the Indicated Action.
Obviously no control will be exerted if no observations of the process output are made (“open loop”). Similarly, measurements by themselves would supply little value if there were not a desired target to compare to, and if this comparison is not made, the size, if any, of the correction needed would be indeterminate. A pre-defined plan of action is essential to avoid “human-in-the-loop” over- and under-correction. The selection of which, if any, corrective action is needed must be based on the objective size of the difference from targets or standards.
It is very important to realize that proper control requires not only the measurements of the process average and its deviation from target, but also the process variation and its deviation from its standard operating range. Only after the process variation is brought under control is the process average a meaningful quantity.
Process control on cooked sausage involves measurement of average values and variation on basic analytical, nutritional, microbiological and sensory properties.
Generally by government regulation or company-imposed standards, the moisture, fat, protein, salt and nutritional content (calories, type of fat, cholesterol, vitamins, minerals and carbohydrates) and microbiological content of the product will be constrained to at least onesided limits.
Process planning and control on such analytical attributes is based on the following typical steps:
Each raw material used (meats, flavorings, etc.) is characterized by laboratory analysis of successive lot samples. The frequency of sampling and accuracy of analysis is tailored to be sufficiently predictive without excess expense.
Each product batch is formulated to obtain a desired target value on each attribute. The target is designed to provide protection against process and material variability causing the actual production lot value from violating the outgoing specification requirement.
For easily measured attributes (moisture, fat, protein), a laboratory analysis of the production blend may be performed, and the error in target reduced by addition of “correction” materials in the final blend.
Samples of production lots are taken as packaged and subjected to quality assurance testing to verify compliance with outgoing specifications.
In addition to analyte attribute control, consumer acceptance of a product requires sufficient consistency in certain sensory properties of the cooked sausage. The attributes of most importance include:
Skin Texture
Bulk Texture or “Bind”
Skin Color
Bulk Color
Saltiness
Sweetness
Flavor (from spice, etc.)
Purge loss
Net Weight
Shrinkage (Moisture loss in processing)
With the exception of net weight, these attributes are subject to only internally-imposed limits. Consequently the means of their control require development of methods not required or sponsored by regulatory organizations. The development of methods of measurement and control has therefore been left to company or university research and has lagged behind the other attributes non-specific to meat products.
3.0 MEAT PRODUCT NON-ANALYTICAL PROPERTIES
The cooked sausage non-analytical properties mentioned above (texture, color, etc.), although not determinable by chemical analysis, are still important to monitor and control.
Skin texture is the chief component of the “bite” of a product. The skin is “tougher” than the product interior provides an initial “snap” during eating. Products with edible (natural or collagen) casings can be manufactured as tough as desired. Skinless products only retain a softer protein-based skin due to smoke, acid and initial oven treatments. A proper balance between skin and internal texture is necessary. Too tough a skin will create the sensation of a “mushy” interior, which may be squeezed out of the skin during biting. Too soft a skin will cause the product to be uniform in texture with little “snap”.
Skin color is principally determined by smoke and acid treatments, and secondarily by the initial oven stage (temperature and humidity) and meat pigment content. Skin color is of importance only in small diameter product, and its darkness is a matter of taste. In products where skin color is important, consistency from batch-to-batch and within-batch is the primary issue.
Bulk texture is the chief component of the “chew” or intermediate and final texture on eating. Too weak a bulk texture and the product will seem “mushy”, too tough and the product will seem “rubbery”. Bulk texture is of critical importance in sliced product, or product with special strength needs, such as corn dogs.
Similarly, bulk color is of importance only in sliced products. Bulk color is determined almost entirely by nitrite level, meat pigment content and the final cook stage time and temperature. Preblend holding time is also a factor.
Saltiness, sweetness and flavor are normally controlled by set addition levels of salt, sweeteners and flavorings in the blend. No measurement normally occurs, with the exception of routine taste tests.
Purge loss or “syneresis” is a serious issue in vacuum packaged products. Significant liquid in the package creates the impression of defective or spoiled product. This liquid is an inconvenience to the consumer (drainage from package after opening) and encourages bacterial growth. Purge loss in bulk-packaged products may cause container damage or contamination, and will affect the net weight per unit of the product at the time of use.
Net weight per package or per unit is a function of stuffing level, process shrink and purge loss. Variation in stuffing level or cook shrink will cause variation in the net weight at the time of packaging. Excessive net weight variation will directly increase product weight “giveaway”. Product used in further processing, such as “corn dogs”, may have problems meeting its final combined product labeling requirements.
4.0 MEAT AS A POLYMER SYSTEM
Meat products have long been subject to mis-classification by researchers using inappropriate technical terms.
In the 1960’s and 1970’s the uncooked meat batter was described as an “emulsion” and the “emulsifying” properties of the meat proteins were thought to dominate the development of cooked product textural attributes. This led to flawed arguments regarding causal relationships between processing, materials used and final product properties.
From the late 1980’s to the 1990’s, researchers discarded the “emulsion” concept for a different viewpoint of a meat “sol” converting to a “gel” upon cooking. These terms are, however, still misnomers since “sol” and “gel” are applicable only to dilute (< 10%) colloidal dispersions.
Technically the uncooked meat mixture is a “paste”, not an “emulsion” or “sol”, since solids content is 40% or more. Upon cooking to a high enough temperature, the “paste” sets to hardened “plastic” material.
Because of these misclassifications, there is considerable confusion in the use of colloid science terms to describe meat systems. To avoid creating an entirely new vocabulary, we will use the current terminology of “gelling” or “gelation” synonymously for “setting” or “hardening”.
“Meat” is the protein-rich flesh of animals. For our purposes here, fish and poultry flesh are “meat”. As stated before, cooked sausage products are a mix of water, fat, protein, salts and carbohydrates gelled and set into a solid mass by the application of heat.
The principal functionality in forming the gelled and set mass comes from the long-chain proteins present and to a lesser extent from the long-chain carbohydrates (starches and gums). When the meat paste is heated above the set-point temperature, the long-chain molecules, supported in solution or at least hydrated by water, are forced to partially uncoil and form irreversiblez cross-linkages. The result is a three-dimensional crosslinked matrix which incorporates the water, fats, salts and fillers within its structure.
A simple paradigm for the mechanism involved is the hard-boiling of a common hen’s egg. The egg is initially liquid and is composed mostly of protein and water with a small amount of fat. When heat is applied above the “set-point” temperature, the protein unfolds and aggregates, forming the rubbery hard-boiled egg consistency. As is obvious, the water component is just as essential as the protein component: dried eggs do not hard boil! The water hydrates the protein molecules and allows mobility for unfolding and crosslinking.
The salts present in the water phase help ionically stabilize the unfolded protein molecules so that its structure can be more easily exposed. The function of salt may be easily seen by adding it to the water used to hard-boil an egg. If the shell is cracked so that a streamer of egg-white is forced out by internal pressure on heating, the presence of salt in the water will cause it to instantly coagulate and seal the crack.
To some extent fats also stabilize hydrophobic protein exposure. They also serve, with other water-insoluble components, simply to fill space and stiffen the protein matrix formed.
Starches and gums will hydrogen-bond and crosslink similar to proteins, and bind appreciable amounts of water. Generally the gelling temperature for such compounds is 90 C or higher, which is seldom obtained in meat processing. Non-gelling or insoluble carbohydrates principally act as mild water binders and matrix fillers. The strength of water-binding is moderate and due to capillary action and hydrogen-bonding, as opposed to irreversible crosslinking. The crystalline nature of a cooled starch gel results in a brittle texture which has little strength after fracture.
Non-meat proteins which are soy- or milk-based (soy flour, soy protein concentrate, soy protein isolate, whey protein concentrate, whey protein isolate, casein) have gel-points of 90 C or more, and function similar to starches in hydrogen-bonding with water to form weak gels at low temperatures.
Since meat’s texture is due to its property of heat-induced long-chain gelling or setting, cooked meat is classifiable as a water-plasticized, filled-cell mixed-composite thermosetting plastic biopolymer.
The word “polymer” denotes long-chain macromolecules which are crosslinked, such as proteins or starches.
The word “plasticizer” indicates that water is the filling solvent that hydrates the polymer and supports its “plastic” behavior.
The word “mixed” denotes possible crosslinking between different polymers, such as different proteins or proteins and cross-linked gums or starches.
The “fillers” present in meat products are fat or insolubles: in rubber tires, it is the carbon that makes the rubber black. Fillers normally will “stiffen” a plastic or rubber, making it harder and less stretchable. Sometimes fillers are active (such as the carbon in rubber tires) and actually bind to the setting polymers present. In this case the filler may increase strength dramatically (ten times or more), and out of proportion to its relative presence on a formula basis.
Additional plasticizer will soften and make more stretchable the polymer matrix. Removal of plasticizer will make the plastic harder and more “brittle” (i.e., less stretchable).
Skin texture in casingless product is formed in a more complicated manner. The proteins are gelled not only through the heat of cooking, but also through the mechanisms of water loss (shrinkage), pH (acid rinse) and smoke application. Therefore only proteins and carbohydrates which gel under these conditions will reinforce “skin” formation. Other materials will in general weaken skin strength by dilution or formation of flaw points.
5.0 TESTING GENERAL POLYMER STRENGTH
In order to understand the significance of tests performed on meat products, it is necessary to first review the mechanical strength principles of the general polymer system.
There is an extensive literature associated with the theory and testing of the mechanical strength or plastics, rubbers and composites. (See Appendix 2.)
The terminology of mechanical properties is vague and confusing, since it has developed to describe the results of very specific test techniques. Appendix 1 gives a glossary of definitions of most common terms.
A typical experiment consists of applying a changing force needed to maintain a constant rate of deformation of a test specimen of specific shape (cross-section and length). The fraction deformation in the direction of force is called the “strain” and the force per unit cross-sectional area is called the “stress”. In experiments where theory is not easily applied, the force and deformation are reported. Where geometry can be analyzed properly, the stress and strain are reported. Force is usually measured in Newtons (N) or kilograms-force (kgf). Deformation is reported as % change. Stress has units of Pascals (usually megapascals, MPa). Strain is dimensionless.
Tests may be performed by compressing, stretching (tension) or twisting (torsion) the specimen. For brittle materials, different strengths are obtained for each mode of testing. For ductile materials, the results from different modes are close.
Measurements of stress and strain for very small deformations allow characterization of the elastic properties of a material, chiefly the Modulus of Elasticity (compression/tension) or Rigidity (torsion).
Large deformations (more than a few %) lead to plastic behavior where the material starts to yield under stress. In this case the quantities of interest are the Maximum Stress and Strain at Maximum Stress. Most tests do not strain the material to more than 25% of its original length, because of unusually behavior occurring when the geometry undergoes large changes.
Viscoelastic and viscoplastic materials are sensitive to the strain rates used in testing: fast rates require higher stresses. As a consequence tests are done at an accepted or specified strain rate, or must be repeated at various strain rates.
Testing done on general polymers falls into three categories:
ELASTIC TESTING: Done at low levels of deformation, usually by oscillatory stressing to determine dynamical properties of the modulus at various strain rates.
FAILURE TESTING: Done at large levels of deformation, usually at a constant strain rate, until the specimen breaks. The reported values are Break Stress and Break Strain.
MODULUS TESTING: Done at fixed levels of strain, such as 90% or 75% (greater than 75% is not recommended). The stress required to achieve this level of deformation is reported.
The dynamical Elastic Testing is normally done only in research. Failure testing is done in research, where usually the whole stress-strain curve is reported, or as an engineering test to quantify the strength at failure. Modulus testing is routinely used in quality control on polymers with important mechanical properties.
Exhibit 2 shows a typical stress-strain curve for a brittle material, such as concrete or styrofoam. Note that at a particular level of strain the material fractures suddenly and the stress required drops to zero.
Exhibit 3 shows a typical stress-strain curve for a ductile or rubbery material, such as polyurethane. Note that after a certain stress or strain occurs, the material starts to yield (become plastic) and the stress drops and appears to fail to a nearly constant value while the material creeps. Once a certain strain occurs, the material becomes harder again (all the “give” used up) and the stress increases to another maximum before the material breaks.
In both Exhibits 2 and 3 you will notice that the initial portions of the stress-strain curves are straight lines (with a slope of the Modulus): this is the Proportional Region. Before the material starts to yield in Exhibit 3, the material would return to nearly its original shape if the stress were removed: this is the Elastic Region. In the testing of rubber-like materials, it is not infrequent to find an absence of the linear Elastic Region. These materials “strain-harden” continuously to a new material whose Elastic Region is approached after noticeable elongation.
In order to specify the mechanical properties of a general plastic, it is usually sufficient to report the Modulus of Elasticity (compression), Modulus of Elasticity (tension), Modulus of Rigidity (shear) and Maximum Stress and Strain for each mode.
6.0 TESTING MEAT PRODUCT GEL-PROPERTIES
The importance of texture has led to a variety of measurement methods in the last three decades. They fall into the raw material and outgoing product test categories.
6.1 SAFFLE “BIND” TEST ON MEATS
The dominant effect of meat salt-soluble proteins on the resulting texture of the product led in the 1960’s and 1970’s to the “Georgia Bind” test of Saffle and co-workers (see Appendix 2 for references).
This test involves the extraction of salt-soluble protein from raw meat samples in a standard way, and then determination of a relative functionality of this salt-soluble protein by an oilemulsification test. The amount of oil sustained in a blender at a particular speed for a particular (10 mg/ml) concentration of salt-soluble protein defines the functionality of that protein. Combining the two effects of % protein salt-solubility and oil-functionality gives the “Bind Constant” or “Bind Index” for the meat.
The “Bind Constants” determined are then used to formulate a product to a specified level of texture, usually specified as the average of
Bind Constant x Protein x 100 %
on a finished weight basis. The resulting “BIND” levels formulated to are typically 200 – 220 % FW for beef products, 180 – 190 for 30% beef and 30% pork products, and 170 – 180 for pork dominant products. Poultry products vary from limits set to 170 – 180 (similar to pork) for products formulated to tighter specifications, to 250+ for chicken franks that are low fat and not adjusted to maximum water content.
The “BIND” values for raw meats are seldom actually measured. Instead, the tabulated results of the Saffle workers are used, possibly adjusted for proximate analysis variations (via the QC Assistanttm of Least Cost Formulations). The presumption is that the “Bind Constants” for the actual meat lots are not too far from the tabulated values, particularly when adjusted for proximate analysis differences.
This “BIND” concept has worked fairly well in practice over the last two decades. Change of the formulated “BIND” of 10 to 15 units will usually result in a sensible change in texture. The standard deviation of measurement of the original “Bind Constants” was approximately 5 to 7%, about the same as the 10 to 15 units is to the 170 to 220 unit limit.
The principal difficulties with the “BIND” concept are:
The concept is inapplicable to many fillers and binders.
The test is not easily repeatable between laboratories because the methodology is sensitive to equipment used.
The effects of processing are not considered and assumed constant.
The effects of fat and moisture are not determinable, other than of dilution, and modern meat products have shifted from 30% fat to 10% fat and lower.
The Saffle “BIND” concept has, whatever its limits, revolutionized meat product formulation accuracy and has provided a basic solution to texture control in cooked sausage.
6.2 OUTGOING PRODUCT COMPRESSION TESTING
The few large meat companies which can afford pilot plants in their R & D facilities will usually also include a Universal Tester system (such as Instron, Chatillon or others).
These testers can perform vertical compression or tension tests at constant strain rates in a heavyduty test stand with a chuck to contain a test probe and a force gauge (of at least 1% full-scale accuracy) to measure the stress applied. The tester provide chart recorder output which indicates force vs time (which gives deformation via the constant strain rate) for the entire crosshead movement.
Because of the design of the machine and the properties of the meat samples being tested, usually a compression test is performed using either a cylindrical, flat probe of 5 to 12.5 mm diameter, or a spherical probe of 5 to 10 mm diameter. The spherical probe test with a 10 mm ball is routinely performed on all lots of surimi.
Universal Testing Machines cost from $5,000 to $20,000 or more, depending on features.
The most reliable compressive test is measurement of the peak force required to puncture the sample. As deformation occurs, the stress rises rapidly and linearly to a first maximum, then undergoes a complex pattern, followed by a second maximum and then failure. Unfortunately there is little consensus as to the shape of the probe (flat vs ball) or which point on the force vs deformation curve to use as the measurement. Some investigators report the first maximum, others the second. It appears that only the first maximum is a reliable predictor of the material properties, since the curve after initial puncture is subject to side friction. In addition, the test results are influenced by the rate of cross-head speed and the diameter of the probe used, all of which vary between investigators.
Other labs report the results of compression to a fixed deformation, such as 90% of height, 80% of height or 75% of height and sometimes even 50%. These tests are particularly difficult to reproduce, since these fixed deformations are not extrema in the force vs deformation curves but instead are on a side slope of rapid change. Consequently slight changes in mounting, deformation or material or cross-head speed may result in significantly different forces being measured.
In the best of circumstances, the precision of the measurement between replicates is 5 to 10%, chiefly due to the incomplete homogeneity of the meat product structure (4 to 6%) and its response to the compressive deformation. Tests are usually run on 5 to 10 replicates to average out within product and instrument variation.
Only the surimi industry has standardized the probe and cross-head speed for the compression test to failure: a 10 mm diameter spherical ball. No standard of any time seems to exist for this type of test in the meat industry.
Because of the inability to apply theory to the complex deformations and unknown contact surfaces involved in the vertical compression test, the results are normally reported as force and deformation rather than stress and strain. A nominal stress of doubtful validity could be obtained by dividing the flat and spherical probe forces by p r2.
6.3 OUTGOING PRODUCT TORSIONAL TESTING
A recent and increasingly popular method of meat product texture measurement is the torsional “gelometer” developed by Lanier and Hamann at North Carolina State University (see Appendix 2 for references).
This system twists a standard hourglass-shaped specimen at a constant angular rate (2.5 rpm = 15 degrees/s) until it fails. The entire stress-strain curve is available, with the maximum stress and strain reported.
The specimen is cut to a standard length (about 20 mm) and plastic plates are glued to each end.
The standard hourglass shape is obtained by chipping a specimen to shape using a special knifetoothed lathe wheel. The sample is necked to 10 mm + 0.2 mm.
The specimen in mounted in a specially modified Brookfield viscometer with a 1% full-scale accuracy digital head. The specimen is rotated by turning the top plastic plate while the bottom plate is held fixed.
This test is relatively well-designed, with the geometry of the specimen chosen to be amenable to theoretical analysis. The force and rotational deformation are easily converted to nominal stress and true strain by the application of formulas incorporating the specimen geometry, rotational speed and effect of twisting.
The stress and strain measured in the NCSU torsional gelometer are statistically independent measurables. The reproducibility of strain is about 4 to 6% standard deviation, and of stress about 5 to 10%. The stress error is inflated by the 5% typical instrument error at the 20% of fullscale encountered on meat products. From 5 to 20 replicates are usually run to average out between specimen and instrument errors.
Because of its sound theoretical basis, the NCSU gelometer is the instrument of choice for research, providing a detailed stress-strain curve for each test. It is, however, much more laborintensive than other test methods, due to milling of the specimen.
The NCSU torsional gelometer is available at a cost of about $15,000 from Drs. Lanier and Hamann (Gel Technology, Raleigh, NC).
7.0 EFFECTS OF MATERIALS AND PROCESSING ON GEL-STRENGTH
Cooked meat products, such as frankfurters or bologna, are, as mentioned before, filled cellular plastics where a three-dimensional cross-linked protein structure encapsulates water, fat and fillers.
Time of chopping or mastication will affect final strength, due to development of active ends of severed protein molecules. In addition chopping reduces fat particle size, breaks the containing fat cell layers, and melts fat droplets allowing surface smearing to take place.
Because meat products are composed of protein macromolecules which retain some alignment of the direction of stuffing, they exhibit “anisotropy” or directionality of strength. The stress and strain to failure will in general differ longitudinally and laterally to the stuffing axis. The effect of stuffing is to pre-stress and pre-strain the product in the direction of stuffing, reducing the longitudinal strain possible and stiffening the gel.
As a product ages in the package after production, it will gradually relax the embedded strain which has been “cooked” into the gel, increasing the strain and decreasing the stress needed for failure.
Filled composites generally exhibit increased strength in compression and decreased strength in tension. Consequently it would generally be expected that adding inert or insoluble materials (and displacing moisture) will stiffen the structure to compression and lower the strain needed for failure. However both stress and strain would be lowered in tension.
As a consequence, adding such fillers not bound to the stronger protein structure would be expected to lower skin strength, where the test condition is perpendicular to the skin, resulting in failure by shear or tension. Such fillers include non-gelling proteins, fats and carbohydrates.
Since moisture functions as a plasticizer, increasing moisture content would imply increased ability to strain, and a softer product (due to displacement of non-liquid ingredients).
Strength and strain at failure will be directly related to protein content: under ideal circumstances proportional to the active protein.
The effect of moisture loss through shrinkage is twofold: a drop in the plasticizer percentage and an increase in the percentage of other materials, including protein. Consequently the strength of a “shrunk” product will be larger than that of the “unshrunk” product by at least the percentage shrink [ 1/(1-s) ], and the strain to failure lower by approximately the shrink [ 1-s ].
Fillers with high water-holding capacity will effectively de-plasticize the system, resulting in ower strains to failure and higher stresses.
The time and temperature the product is cooked at will have a modest influence on the gel strength. Product cooked to 5 C or 10 C higher temperature or for 10 minutes longer will generally gel more fully, resulting in both increased stress and strain at failure. Since the gel process is analogous to the microbiological “kill” effect of cooking (bacteria are proteins too!), it is easy to see that cooking has a natural completion, where nearly 100% conversion occurs. Therefore very short cook cycles the lowest final temperatures will exhibit the greatest sensitivity to these variables.
The effects of salt level are to shift the pH sensitivity of the proteins and stabilize functional groups to the surrounding water. Higher salt levels generally will increase strength due to greater protein mechanical extraction, greater unfolding (resulting in increased cross-linkages) and lower the gel point temperature (resulting in more complete gelling in the cook cycle).
The effects of phosphate or lactate include:
1) increase in ionic strength (salt effect),
2) increase in pH and
3) special interactions to stabilize unfolded proteins.
Skin formation is generally due only to the meat myofibrillar proteins. The higher shrink losses from the skin areas mean the structure is pre-strained and stressed. Displacement of the moisture plasticizer by any non-bonding materials will generally decrease the strain to failure, making the skin more brittle. Since the skin properties of interest are normally tensile or shear strengths, such fillers will generally also decrease the skin strength, or at best leave it unchanged.
The mechanism for meat product deformation of 100% to 150% before failure is due to the protein chain length. The long protein molecules may be visualized as springy coils which are crosslinked to neighboring coils in random patterns. When strain occurs in a specific direction, the protein molecules uncoil into a more linear conformation. This requires free space (solvated by plasticizer) and mobility to accomplish. Clearly there is only so much “uncoiling” that can occur: if pre-stretching is accomplished by volume compression due to cook shrink or by stuffing distortion, less deformation will be available during testing or eating.
The protein content of cooked meat products is usually between 10 and 20% of the composition, or a minor constituent compared to moisture and fat. Consequently the stress and strain observed for a product will increase at least linearly with protein, and quadratically for low levels of protein.
Collagen protein contracts by 10% or more upon reaching its gel-point of 60 C, and therefore has the effect of straining the entire thermoset product.
Fat generally expands by 10% or more upon melting, and therefore stresses and strains the product before complete setting has taken place. It is essential that the fat droplets be coated with a closed-cell protein structure or embedded in a strainable gel to protect the structure against fracture by fat expansion with concomitant leakage of liquid fat along these fractures to relieve the stress imposed.
It is an interesting fact that most cooked muscle foods exhibit a modulus of rigidity between 10 and 20 kPa (see Exhibit 4).
The ultimate stress needed for a particular product will change substantially with the temperature at time of test. The viscosity of the fat present will change markedly below room temperature as the fat congeals and becomes crystalline. The stress needed at 35 F may be twice that at 70 F. The ultimate stress above room temperature should drop at least linearly with increasing temperature up to the gel-point at a rate of 0.1 – 0.3% per degree C.
8.0 SKIN VS BULK STRENGTH
As mentioned in the last sections, there is a fundamental difference in the mechanical properties of interest of the skin and of the bulk product:
PROCESSING: Skin properties are primarily and directly affected by processing steps such as smoke treatment, acid treatment and early cook stages. Bulk properties are, however, primarily affected only by the final cook stage.
TENSION vs COMPRESSION: The skin is bitten through perpendicular to its surface, so strength in tension and shear are the quantities of interest. The bulk interior is masticated by chewing, which means that strength in compression and shear are the quantities of interest.
FILLERS: Fillers, such as fats, carbohydrates, non-meat proteins, etc., generally will decrease skin strength, even though the meat protein level stays the same, but will generally increase the bulk strength, even if the moisture level is unchanged.
MECHANICAL SUPPORT: Testing of specimens for skin strength involve imposition of perpendicular loads to a thin layer, drawing upon mechanical support from the product surface large distances away. On the other hand, bulk compression or shearing remains local, so long as the test probe used is small in invasive volume. As a consequence, independent measures of skin strength and bulk strength should be made.
9.0 SENSORY FACTORS INFLUENCED BY GEL STRENGTH
The “+” in the above table indicates the parameter is positively highly correlated with the factor (e.g., increasing maximum stress increases hardness). A “-” indicates the parameter is negatively correlated with the factor (e.g., increasing maximum stress lowers ease-of-swallow). No entry in the table indicates no significant direct correlation.
As mentioned before, skin and bulk texture need to be considered separately. A “good” frank, for example, should have enough skin strength to provide a noticeable “snap”, but not so strong that it is difficult to bite or so that the frank “bursts” on eating. The bulk texture should be strong enough to be “chewy”, but not so strong as to appear “rubbery”. Some markets (e.g., Far East) or some products (e.g., canned Vienna sausage) may require a “mushier” product standard than North American franks.
10.0 TYPICAL LOT-TO-LOT VARIATION IN A FRANKFURTER’S TEXTURE
Exhibit 5 shows an actual record the ultimate stress (as determined by the NCSU torsional gelometer) of successive batches of a frankfurter over days of production.
EXHIBIT 1: PROCESS CONTROL LOGIC
EXHIBIT 2: FORCE-DEFORMATION CURVES FOR BRITTLE PLASTICS
EXHIBIT 3: FORCE-DEFORMATION CURVES FOR DUCTILE RUBBERS
EXHIBIT 4: STRESS-STRAIN RELATIONSHIP FOR MEATS
EXHIBIT 5: TYPICAL LOT-TO-LOT VARIATION IN STRESS FOR A FRANK
APPENDIX 1: GLOSSARY
Binder: In a composite plastic, the continuous phase that holds together the reinforcing materials.
Break, Failure or Fracture Strength: The stress at the breakpoint.
Break, Fracture or Failure Point: The discontinuous point at which the specimen separates and the stress drops to zero rapidly.
Brittleness: The property of a material to fail under a small deformation.
Brittle materials usually behave differently under tension and compression.
Brittle materials are usually weak in tension and strong in compression.
Cell: A small cavity surrounded partially or completely by walls.
Cell, Open: A cell not totally enclosed by its walls.
Cell, Closed: A cell totally enclosed by its walls.
Colloid: A substance in an extremely fine state of subdivision dispersed in a continuous medium, where the principal properties of surfaces and interfaces play the dominant role.
Colloidal solution: A dilute colloidal dispersion of a lyophilic particles, usually molecularly dispersed and thermodynamically stable as a single-phase system.
Creep: The time change of strain under a fixed stress.
Crosslinking: The formation of a 3-dimensional polymer by means of interchain reactions resulting in changes to physical properties.
Deformation: The decrease in length from the gage length due to compressive force applied.
Dilatant: A material which hardens upon imposed shear. (Opposite of “Thixotropic”.)
Disperse phase: The discontinuous phase of a colloidal mixture.
Dispersion medium: The continuous phase of a colloidal mixture.
Ductility: The property of a material to have large plastic deformations without rupturing.
Ductile materials have almost identical tension and compression stress-strain curves.
Elasticity: The property of returning quickly and completely to initial geometry after unloading.
Elastic Limit: The greatest stress to which a material may be subjected without permanent strain resulting (i.e., the specimen recovers its original dimensions).
Elastomer: A macromolecular material that at room temperature returns rapidly to approximately its original dimensions and shape after a substantial deformation by a weak stress.
Elastoplasticity: The property of retaining partially and permanently a deformation after unloading.
Electrophoresis: The movement of particles with respect to a liquid as a result of an applied electric field.
Elongation or Extension: The increase in length from the gage length due to the force imposed.
Emulsion: A stable dispersion of one liquid in another, usually water and an oil or organic compound. Two types exists: oil-in-water (“O/W”) and water-in-oil (“W/O”), depending on which compound is the disperse and which is the continuum phase. Stability requires the presence of a third material, an “Emulsifying Agent”, which stabilizing the oil/water interface.
Fiber: A plastic which has been crystallized by “Strain Hardening” to form a greatly stronger oriented or interlocking structure longitudinally.
Filler: A sometimes inert and sometimes functional material added in the particulate solid phase to a plastic to modify its properties or lower its costs. If functional to a high degree, they are called “Reinforcing Fillers”.
Flexibility: The property of a material to have large elastic deformations without rupturing.
Foam: Gaseous dispersion (usually air) in a liquid continuum.
Gage Length: The original length of a test specimen over the portion over which the strain is being determined. For tensile or compressive tests, the height of the narrow region. For torsional tests, the circumference of the narrow region.
Gel: A two-component semi-solid system, rich in liquid (< 10% gelling component), made of a network of solid aggregates in which liquid is held. A hardened “sol”.
Gelation: The process of hardening or “setting” of a sol into a material with solid-like properties.
Gel-Point: The stage at which a liquid mass begins to exhibit pseudo-elastic behavior, the inflection point in viscosity vs time.
Glass: A product of freezing, typically hard and brittle, which has cooled to rigidity without crystallizing.
Glass Transition: The reversible change over a relatively small temperature region in amorphous polymers to a viscous or rubbery condition from a hard and brittle condition.
Glass Transition Temperature: The approximate midpoint of the temperature range over which a glass-to-rubber transition occurs. Hofmeister series: See “Lyotropic Series”.
Hydrocolloid: A material capable of forming a colloidal suspension in water.
Hydrogel: A gel formed from a material dispersed in water as a medium. Hydrophilic: A disperse phase which has a high chemical affinity for the water dispersion medium.
Hydrophobic: A disperse phase which has a low chemical affinity for the water dispersion medium.
Lyophilic: A disperse phase which has a high chemical affinity for the dispersion medium.
Lyophobic: A disperse phase which has a low chemical affinity for the dispersion medium.
Lyotropic series: A series of cations or anions in order of coagulating power (e.g., Li+ > Na+ > K+ or Cl- > Br- > I-).
Micelle: A submicroscopic aggregate of colloidal polymers usually oriented with respect to a dispersion medium (lyophilic out and lyophobic in).
Modulus of Elasticity or Elastic Modulus or Young’s Modulus: The slope of stress vs strain below the proportional limit in tensile or compressive testing.
Modulus of Rigidity: See Shear Modulus.
Necking: localized reduction in cross-section in tensile tests.
Nonrigid Plastic: A plastic which has a modulus of elasticity of 70 Megapascals or less. All cooked food gels have moduli of 1 MPa or less.
Pascal: A unit force of 1 Newton applied to a cross-sectional area of 1 square meter. 1 atmosphere of pressure is 101325 Pa or 101.325 kPa or 0.101325 MPa.
Peptization: From analogy to peptic digestion, the spontaneous dispersion of a precipitate to form a colloid.
Percentage Elongation: The elongation expressed as a percentage of gage length. Different percentage elongations will be observed at yield and at break.
Paste: A concentrated (> 10% by volume) dispersion of solid particles in a liquid continuum.
Plastic: A material that has as an essential ingredient one or more organic macromolecule, is solid in its finished state, and at some stage in processing can be shaped by flow. Rubbers, textiles, adhesives and paint are not classified as plastics.
Plasticity: The property of retaining permanently and completely a deformed shape after unloading.
Plasticizer: A substance incorporated in a material to increase its workability, flexibility or distensibility.
Plastisol: A plastic or resin dissolved in a plasticer to give a pourable liquid.
Polymer: A substance consisting of repeating units of one or more monomers.
Proportional Limit: The greatest stress for which stress vs strain is a straight line through the origin.
Purge: The syneresis of water from a meat product over time.
Rate of Straining: The change in nominal strain per unit time. Plastic materials become “stiffer” when faster deformations are required. Consequently results at different strain rates will generally differ significantly in a systematic manner. For non-rigid materials, usually 1.5 per minute (150% elongation in 1 minute or 2.5% per second).
Rate of Stressing: The change in nominal stress applied per unit time. See Rate of Straining.
Reinforced Plastic: A plastic with high-strength fillers embedded, resulting in mechanical properties enhanced over the unfilled plastic.
Rheology: The study of mechanical properties, particularly flow, ductility and plasticity, or concentrated colloidal systems.
Rubber: A material capable of recovering from large deformations quickly and forcibly. From a test point of view, a rubber will retract from 100% elongation to 50% elongation in less than 1 minute at room temperature.
Shear Modulus of Elasticity or Modulus of Rigidity: The slope of shear stress vs strain below the proportional limit in torsional testing.
Sol: The dilute (less than 1% by volume) dispersion of a lyophobic solid in a liquid or gaseous medium. The dispersion medium is usually denoted by a prefix, such as “hydrosol” (water) or “aerosol” (air).
Strain or Nominal Strain: The ratio of elongation or compressive deformation to gage length. If the specimen retains its original dimensions, the strain is 0. Note that, as with nominal stress, strain may not be meaningful if the specimen geometry is seriously distorted during test.
Strain Hardening: The process of increasing strength by elongation by strain to produce apartially crystallized fiber.
Strength, Nominal: The maximum nominal stress sustained by the specimen during the test.
Stress, Nominal: The force per unit area (N/m2 = Pascal) of minimum original cross-section. If the specimen deforms significantly under test (“yields”), necking, stretching or bulging may occur to an extent that the nominal “stress” is not a meaningful quantity.
Syneresis: The spontaneous shrinkage of a gel to form a more concentrated gel and free exuded dispersion medium.
Thermoplastic: A plastic that can be repeatedly softened and hardened by heating and cooling to and from a flow-shapable state.
Thermoset: A plastic that, after having been cured by heat or other means, is substantially infusible and insoluble.
Thixotropic: A material which has lowered viscosity on increased shear (e.g., liquefied by shaking). Notable example is quicksand, which acts liquid under force.
Toe Compensation: The correction for the initial “ramp-up” of stress required to take up equipment slack at the start of testing.
Toughness: The property of a material to withstand large deformations or stresses before failure.
True Strain: The strain corrected for known standard geometry changes necessary under test which affect length. For a tensile test, true strain is the natural logarithm of 1 plus the nominal strain (ratio of after to before length).
Ultimate Strength or Maximum Strength: The maximum stress encountered during testing.
Viscoelasticity: The property of continuously creeping under load and continuously retreating after unloading, with a return to original form after some lapse of time.
Viscoplasticity: The property of continuous creeping under load and a retention of the deformed shape after unloading.
Viscosity: The resistance to flow within the body of a material.
Work to Failure or Fracture: The integrated force through deformation or stress through strain to cause breakage or rupture of the specimen. A measure of “Toughness”.
Yield Point: The first point at which the strain increases without an increase in stress. Usually at a maximum in stress, but may also be at an inflection point in stress.
Yield Strength: The stress at the yield point.
APPENDIX 2: BIBLIOGRAPHY
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In order to understand fine emulsion products better, as it is manufactured in South Africa, we have to understand soya. I turned to Prof. Zeki Berk’s 1992 work when he was at Technion, Israel Institute of Technology, Haifa, Israel. The work was titled Technology of Production of Edible Flours and Protein Products from Soybeans.
What follows is a selection of quoted sections from his book relevant to our discussion on emulsion sausages and polony. By way of introduction, let me make a few notes about Zeki Berks (1931-2019) based on an obituary written by Prof. Sam Saguy (19.07.2019).
In our trade we stand on the shoulders of giants. I have done a review of the men and woman who brought about the current understanding and methods used in meat curing in my article, Fathers of Meat Curing. Here is another giant on whose shoulders we stand in our understanding of soy processing! It was thrilling to discover a work by a consummate professional and talented academic on such a subject. Right from the start, I was struck by the quality of his work. I looked for details on him and was saddened that he passed away last year. It is nevertheless a thrill to know that I am taught, as it were, by a man from beyond the grave, as we are often influenced by the lives of people who are no longer with us.
Prof. Saguy wrote about Zeki Berk, “For all his numerous students around the world, he was an icon, beacon and the compass who taught and implemented basic and applied science, technology and devoted his life to education and excellence. In addition, he was also a person that symbolized more than probably anything else being kind, receptive, a great listener and above all redefining the meaning of a ‘Mensch’. His delightful and brilliant cooking skills as well as his amazing linguistics knowledge were extraordinary.”
“Zeki was a chemical engineer and food engineer and scientist with a long history of work in food engineering, including appointments as a professor at the Technion The Israeli Institute of Technology (IIT), M.I.T. and Agro- Paris, and as a consultant at UNIDO, FAO, the Industries Development Corporation, and Nestle. He was the recipient of the International Association of Food and Engineering Life Achievement Award (2011), and the first recipient of the Academic Life Time Achievement Award from the Food Industry Association-Manufacturers of Israel (2001). Prof. Berk wrote/edited 7 books and numerous papers and reviews.”
I decided to quote his work here to add it to my own collection of invaluable resources for quick and easy access.
1. Utilization of Soy
Berk (1992) authored a comprehensive review of soy production, published in 1992. The data may be outdated, but his review is as relevant today as the day he wrote it.
The various uses of soy in 1986 are given below.
2. How Soya is Processed
– Roasting and Grinding Whole Soy
In my review of the health concerns associated with soya (Soya: Review of Health Concerns and Applications in the Meat Industry), I noted that roasting soya has been practised from as early as 300 BCE and milling it from before the Han dynasty (202 BC–220 AD). It is some of the oldest processing technology known for soy.
Berk (1992) writes that roasted whole soybeans and their flour are used as ingredients in China, Japan, Korea and Indonesia. I am very interested to know what this looks like in practical terms and will make this the subject of a future investigation. Besides ingredients, roasted whole soybeans and its flour are also used in traditional confectionery products and snacks in the same countries.
Another very interesting utilisation is that of immature whole green soybeans which are consumed as a vegetable. The use of the small plants has been practised from antiquity. By the time of the Han dynasty, it was already practised. Cooking the mature dry soybeans the way we do with other legumes ( such as navy beans, black beans, chickpeas or lentils) as was done in antiquity is seldom done even in the traditional areas of soybean consumption. “The reason for this may have been the persistent bitterness and “green beany taste” of soybeans, the low starch content, the relatively low water adsorption (swelling) capacity, long cooking time and poor digestibility.” Berk (1992)
– Soy: Oil Mill
“This option starts with the separation of the soybeans into two fractions: oil and meal. I deal with them side-by-side in the columns below. There are, basically, two process alternatives to achieve this purpose: pressing and solvent extraction. Each one of the fractions is then further processed to yield a multitude of products and by-products, with practically no waste. Since oil meal operations are often the starting point in the preparation of soybean protein products, they will be reviewed in some detail later in this article. The processes and products associated with the oil fraction will be described here in some detail. Soybean protein products which branch-off from the meal fraction will now be just mentioned for the sake of completeness and taken up in detail further on.” Berk (1992)
Oil Fractions
“The preparation of marketable soybean oil for human consumption from crude soybean oil requires a series of operations known as ” refining “. Several alternative technologies are available for each one of these operations. Each one can be carried out in batchwise, continuous or semi-continuous fashion.
The first step in refining crude soybean oil is the removal of the phospholipids, or “degumming“. Degumming is necessary in order to prevent the separation and settling of gums (sticky, viscous oil-water emulsions stabilized by the phospholipids) during transportation and storage of crude oil, to reduce oil losses in the subsequent phases of refining and to avoid excessive darkening of the oil in the course of high-temperature deodorization. Crude oil is mixed thoroughly with a small amount of water and an acid (usually phosphoric acid). “Gums” are formed and precipitated, carrying in the emulsion a certain amount of oil. They are separated by centrifugation, dried under vacuum and bleached. The resulting product consists of approximately 50% phospholipids and 50% oil and has the consistency of honey.
The phospholipid fraction may be separated from practically all the oil by a series of solvent extraction and precipitation processes. Oil-free soybean phospholipids are solid. All these by-products of the degumming process are known as “soybean lecithin” and sold under different trade-names and in a variety of quality grades. The principal quality parameters for commercial lecithins are phospholipid content (measured as percent acetone insolubles), free acidity, non-lipid impurities (measured as hexane insolubles), viscosity and colour. For certain applications requiring an extremely bland lecithin, the phospholipids are separated from the crude soybean oil fraction, purified and then redissolved in any desired type of refined oil. Lecithins are mainly used for their activity at the interface between fats and hydrophilic phases. They act as emulsifiers in sauces and salad dressings, as viscosity reducers and stabilizers in chocolate, as anti-spattering agents in margarine, as pan release agents in bakery and confectionery, as dough improvers and staling retardants in bread, as wetting agents in instant food powders etc. They also have some antioxidant property.
Degumming is usually carried out at the extraction plant, even if the subsequent steps of refining are performed elsewhere. Whenever further processing of the crude gums is not economically feasible, due to insufficient plant scale or insufficient market demand, the crude gums can be added back to the meal, increasing the bulk and caloric value of the latter.
There are two major types of processes for refining degummed oil. They differ in the way the free fatty acids are removed. In the “chemical ” or “caustic” refining process, the most common process applied to soybean oil, the fatty acids are neutralized with alkali (sodium hydroxide and sodium carbonate) to form salts (soaps) soluble in water. Treatment with caustic solutions also removes residues of phospholipids not removed by degumming and results in some degree of bleaching due to the destruction of some of the pigments or their adsorption by the heavy phase.
The resulting aqueous soap solution, known as “soap stock” is removed from the neutralized oil by centrifugation. The amount of alkali to be added is calculated according to the free fatty acid content of the oil plus a slight excess (about 0.1%).
Crude soybean oil contains typically 0.3 to 0.7% free fatty acids. After neutralization, the oil is thoroughly mixed with hot soft water to remove traces of soap (washing ), then centrifuged again and dried by heating under vacuum, in preparation to the next step, bleaching. Soap stock can be used for making soap or it can be converted back to fatty acids by treating with a strong mineral acid. The crude mixture of fatty acids obtained, known as “acidified soap stock” can be used as a caloric component in animal feed or for the manufacture of distilled fatty acids. In the “physical refining” process, less commonly applied to soybean oil, fatty acids are removed by steam distillation under high vacuum, simultaneously achieving deodorization. Oil for physical refining must be degummed more thoroughly than in the case of alkali refining process.
The next step of refining is “bleaching‘. Its purpose is to remove the yellow-orange carotenoid pigments and the green chlorophyll of the oil. The extent of bleaching depends on market requirements. The market in the U.S.A. requires almost water-clear appearance while somewhat darker colour may be perfectly acceptable or even preferred in other markets. Bleaching is carried out by treating the oil with solid adsorbents such as Fuller’s earth or activated carbon or both. The pigments and some other impurities are adsorbed on the solid surface and removed by filtration. In order to prevent oxidation, the process is carried out under vacuum. Continuous “in-flow” bleaching processes are available.
The last refining operation is “deodorization“. It consists in the removal of odorous substances by steam distillation under high vacuum and at temperatures in the range of 2500 C. Typically, the deodorizer is a vertical cylindrical vessel with internal baffles and other devices to ensure exposure of a large surface area of oil and intimate contact between the oil and steam. At the end of the stripping process, the oil must be cooled while still under vacuum to prevent oxidation. Citric acid is usually added in order to chelate any metal ions which may catalyze peroxide formation. In modern deodorizers, all the parts in contact with oil are made of stainless steel to prevent such metal contamination. While the main objective of deodorization is the removal of odour-bearing compounds such as aldehydes, ketones and hydrocarbons, other substances such as sterols and tocopherols are also distilled off. In physical refining, this operation is responsible for the removal of free fatty acids. All these substances may be recovered from the deodorizer condensate stream, if necessary.
b- Further processing and utilization of refined soybean oil: Freshly refined soybean oil is practically odourless and bland. However, objectionable off-flavour described as “green, grassy, fishy” is known to develop quickly if the oil is heated (as in cooking and frying), or stored under conditions which expose it to light and oxygen or permit contamination with certain metals such as copper and iron.
This type of flavour deterioration has been called “flavour reversion”, expressing the thought that it brings back the off-flavours of crude oil. Although this has been shown to be false, the term of “flavour reversion” is still used sometimes, when referring to the flavour deterioration of refined soybean oil. The process is apparently triggered by the oxidation of the unsaturated fatty acids and most particularly that of linolenic acid. Unlike oxidative rancidity, flavour reversion occurs at very low levels of oxidation and is not retarded appreciably by antioxidants. It can be retarded by minimizing exposure to oxygen (bottling under nitrogen) and to light (opaque containers, dark glass bottles).
Another method of flavour stabilization is the reduction of the linolenic acid content by selective hydrogenation, followed by chilling (winterization) to remove the high melting point saturated fatty acids formed. The partially hydrogenated- winterized soybean oil is perfectly suitable as an all-purpose (salad and cooking) oil. The crystalline fraction separated after chilling is known as “soybean stearin” and used in different solidified fats.
More complete hydrogenation of soybean oil is the basis for the manufacture of shortenings, margarines and tailor-made fats used by various food industries”. Berk (1992)
Meal fraction
“a- Soybean meal as animal feedstuff: By far the largest portion of the soybean oil meal and cake production is used as a protein source in animal feed. Although the terms “meal” and “cake” are often used interchangeably, meal refers to the product of solvent extraction, while cake is the product resulting from expeller pressing of soybeans. The different types of soybean meals are characterized mainly by their protein content and the extent of heat treatment applied in their production to inactivate anti-nutritional factors. If the soybeans are extracted without dehulling, or if the hulls are added back after extraction, the meal will contain about 44% protein. Meals produced from dehulled beans contain approximately 50% protein.
The extent of heat treatment or toasting is measured in terms of residual urease activity or as the solubility of the protein under specified conditions ( Nitrogen Solubility Index NSI, or Protein Dispersibility Index PDI ).
The optimal degree of toasting depends on the final application. Thus, meal for poultry rations must be toasted much more thoroughly than meal for use in cattle feeds. Considerable efforts have been made to develop in vitro laboratory tests capable of predicting the nutritional performance of soybean meal in feed rations. The most widely used methods are: urease activity, trypsin inhibitor, dye-binding, fluorescence, protein solubility in water or alkali and available lysine. All these tests refer to the heat treatment history of the meal.
b- Defatted soybean flours and grits: These products, intended for human consumption, are essentially soybean meal which has been ground to the appropriate mesh size. The starting material is dehulled beans and strict sanitary requirements are applied to processing, storage and packaging conditions, in order to secure the microbiological quality of the final product (e.g. total microbial count). In addition, a large variety of products, differing in their lipid content are produced by adding back soybean oil and/or lecithin to defatted flour or grits at specified levels (refatting).
c- Soybean protein concentrates: Products containing about 70% protein are prepared from defatted meal by selective extraction of the soluble carbohydrates (sugars). Extraction with aqueous alcohol is the most common process, but other methods of production are available. The concentrates are essentially bland.
d- Soybean protein isolates: Even higher concentrations of protein, in the order of 96%, are obtained by selective solubilization of the protein (e.g. alkaline extraction), followed by purification of the extract and precipitation of the protein (e.g.by acidification to the isoelectric point). Isoelectric isolates are insoluble in water and have practically no functional features. They can be converted to sodium, potassium or calcium proteinates by dissolving isoelectric protein in the appropriate base and spray-drying the solution. Sodium and potassium proteinates are water soluble. They are used mainly for their functional properties, such as emulsification or foaming. One of the by-products of the protein isolation process, the insoluble residue, is also commercialized for its remarkable water absorption capacity and as a source of dietary fibre.
e- Extrusion-textured soybean protein: If defatted soybean flour with a specific moisture content is subjected to high shearing forces at high temperature in an extruder, a product with a peculiar laminar structure is obtained. After hydration, this product presents an elastic and chewy texture resembling that of meat. The product is known as “textured soybean protein” or “textured vegetable protein” (TVP).
TVP with higher protein content is made by extrusion of soybean protein concentrates.
f- Spun fibres of soybean protein: The well-established technologies for making synthetic fibres can be applied to soybean protein. Isolated soybean protein is dissolved in strong alkali and the solution is allowed to age until it has the consistency of honey. The viscous liquid, known as “dope” is then injected into an acid bath, whereby the protein precipitates in the form of fine fibres. The fibres are stretched, washed and collected as bundles. Spun fibres of soybean protein are used in the manufacture of a variety of meat analogs, to which they impart the fibrous aspect and bite of animal muscle.” Berk (1992)
Full-Fat Soya
The application of heat removes the anti-nutritional factors of soy. As we have seen in my article, Soya: Review of Health Concerns and Applications in the Meat Industry, is not such a big factor for humans, but later in this article, we will show it has an immense impact on animal nutrition. A heating step before processing begins makes the oil also more accessible. Ottevanger Milling Engineers give the following process overview.
Cleaning – at the start of the soybean processing, it is important to remove stones with a destoner, metal parts with a magnet and small grit & fines with a vibrating sieve.
Crushing – a crusher will crush the bean in 4-8 particles, leaving the skin and crushed soybean. The hulls are removed from the crushed pieces through a wind sifter.
Temperature – the crushed soybeans are brought up to temperature by adding steam in a conditioner. A toaster is used to keep the crushed soybeans at temperature for a longer period of time.
Expansion – we use the expander for the expansion of the crushed and conditioned soybean into full-fat soy.
Steam – the application of steam on the conditioner, toaster and expander is used to heat up and keep the product warm in order to improve gelatinization.
Cooling – after expansion the product will be cooled to bring the product back to an ambient temperature.
This process is used to create full-fat soya, but you can see the important step of steam application right at the start of the process. (Ottevanger Milling Engineers)
3. OIL-MILL OPERATIONS
Operation principles
Continuous pressing by means of expellers (also known as screw presses) is a widely applied process for the extraction of oil from oilseeds and nuts. It replaces the historical method for the batchwise extraction of oil by mechanical or hydraulic pressing. The expeller (seen below) consists of a screw (or worm), rotating inside a cylindrical cage (barrel). The material to be pressed is fed between the screw and the barrel and propelled by the rotating screw in a direction parallel to the axis. The configuration of the screw and its shaft is such that the material is progressively compressed as it moves on, towards the discharge end of the cylinder. The compression effect can be achieved, for example, by decreasing the clearance between the screw shaft and the cage (progressive or step-wise increase of the shaft diameter) or by reducing the length of the screw flight in the direction of the axial movement. The gradually increasing pressure releases the oil which flows out of the press through the slots provided on the periphery of the barrel, while the press-cake continues to move in the direction of the shaft, towards a discharge gate installed at the other extremity of the machine.
Before entering the expeller, the oilseeds must be cleaned, dehulled (optional), flaked, cooked and dried. Flaking facilitates oil release in the press by decreasing the distance that the oil will have to travel to reach the particle surface. Cooking in the presence of moisture is essential for the denaturation of the proteins and, to some degree, for the coalescence of the oil droplets. Cooking plasticizes the flakes, renders them less brittle and thus reduces the extent of flake disintegration as a result of shear in the press. Extensive flake disintegration would reduce oil yield and produce a crude oil with a high content of fine solid particles (foots). After cooking, excess moisture is removed in order to avoid the formation of muddy emulsions in the press. Cooking is usually achieved by mixing the flakes with live steam. Additional heat may be provided by indirect steam, while thoroughly mixing the mass.
3-1-2 Advantages and disadvantages of the expeller process
Expellers can be used with almost any kind of oilseeds and nuts. Therefore, in a multi-purpose plant built to process different types of raw materials and not only soybeans, the expeller process may prove advantageous. The process is relatively simple and not capital-intensive. While the smallest solvent extraction plant would have a processing capacity of 100-200 tons per day, expellers are available for much smaller capacities, from a few tons per day and up.
The main disadvantage of the screw-press process is its relatively low yield of oil recovery. Even the most powerful presses cannot reduce the level of residual oil in the press-cake below 3 to 5%. In the case of oil-rich seeds such as sesame or peanuts, this may still be acceptable. Furthermore, most of the oil left in the cake can be recovered by a stage of solvent extraction. Such two-stage processes (pre-press/solvent extraction) are now widely applied. In the case of soybeans, however, a 5% residual oil level in the cake represents an oil loss of about 25%. Solvent extraction of the cake would not be economical, because of the bulk of material which must be processed. Pre-press/solvent extraction processes are, therefore, not applied to soybeans.
The commercial value of the meal is usually higher than the income from sales of the corresponding quantity of oil. The quality of the meal is therefore a factor of particular importance in the selection of a processing method for soybeans. In this respect, the expeller process has several disadvantages. The first is the poor storage stability of the press-cake, due to its high oil content. Furthermore,the extreme temperatures prevailing in the expeller may impair the nutritive value of the meal protein, mainly by reducing the biological availability of the amino acid lysine. At any rate, expeller press-cake is not suitable for applications requiring a meal with high protein solubility.
3-1-3 Equipment
Unlike solvent extraction equipment which is supplied by a relatively small number of manufacturers, screw presses with a widely varying degree of sophistication are available from a multitude of sources. Yet, considerable technical improvement and advanced features can be found in the models offered by the leading manufacturers. Such features include: multi-stage pressing to increase oil yield, better feed rate control, water cooled barrel and shaft, ease of maintenance and repair, improvements in the drive and transmission, sanitary construction, safety features etc. Most press manufacturers also supply cooker-dryer units, designed to operate with the press. Cooker-dryers may be horizontal (jacketed screw conveyor type), but the most common types consist of vertical stacks of round chambers (rings) equipped with paddle stirrers.
This design is indeed very common in operations for heat treating oilseed material and will be encountered in flake conditioners, desolventizers, meal dryers and coolers.
3-2 The solvent extraction process
3-2-1 Operation principles
A flow diagram describing the solvent extraction process for soybeans is given in the figure below. The process consists of the following stages:
a- Receiving and storage of soybeans. b- Preparation of the raw material for extraction. c- Solvent extraction. d- Recovery of the solvent from the extract (micella). e- Desolventizing/toasting of the meal.
3-2-2 Receiving and storage of soybeans
Nowadays, soybeans are received at the factory, almost exclusively in bulk, by truck or rail. They are weighed, unloaded and conveyed to the main storage silos. The size of the silos depend on the frequency of reception and the availability of other storage facilities in the region. Normally the main storage volume should correspond to the raw materials needed for a few months of operation at full capacity.
Pneumatic conveying is used in large installations while mechanical conveyors and elevators are more common in smaller plants. It is extremely important to maintain good sanitary conditions on and around the receiving areas and especially, to protect the seeds from contact with moisture. The receiving area, which consists of outdoors installations with a fair amount of movement of people and vehicles, tends to be one of the most critical parts of the factory, from the sanitation point of view.
As soybeans are purchased by grade, it is necessary to draw representative samples for quality evaluation from each lot at the point of reception. The samples are analyzed for moisture, foreign materials, colour, broken beans etc. in order to determine the compliance of the lot with the specified grade criteria. It is also advisable to determine oil and protein content, free fatty acids and other quality factors for the sake of proper bookkeeping, even if these criteria are not part of the standard grading and pricing system.
The typical storage facility in soybean oil plants is the vertical cylindrical silo. In recent years the conventional concrete silo is being replaced by steel silos of different types. A recent innovation in this area is a silo construction method based on the use of a steel strip wound in the form of a continuous spiral, each winding being fastened to the next one by crimping. The steel strip is supplied as compact coils, thus reducing the cost of transportation of bulky pre-fabricated constructions. One of the advantages of the metal silos is the speed of erection.
3-2-3 Preparation for extraction
This stage comprises drying, tempering, cleaning, classification (optional), cracking, dehulling (optional), conditioning and flaking. A flow diagram for the conventional preparation of soybeans prior to solvent extraction is given in below.
a- Drying: If the soybeans are to be dehulled before extraction, they must be dried to a moisture content below 10% in order to facilitate separation of the hulls. This is achieved in vertical gas or oil fired forced circulation driers. If the natural moisture content of the beans is 10% or less, or if dehulling is not practised, drying as a preparation step can be omitted.
b – Tempering:After cooling, the dried soybeans are stored in bins for 2 to 5 days, in order to allow for moisture equilibration by diffusion. This is called tempering. The tempering bins, which are usually outdoors silos of the vertical type, also serve as working bins (day bins), to secure uninterrupted feeding of the plant. As all the subsequent steps of processing are continuous, it is necessary to monitor the flow of soybeans from the working bins to the processing plant, in accordance with the planned processing capacity. This is done by means of automatic balances installed at the feed-end of the line.
c – Cleaning:The soybeans are subjected to a number of cleaning operations throughout the process. Tramp iron is removed by magnetic separators. In moderate capacity installations, these can be magnets attached to conveyors or chutes carrying a stream of beans. For larger plants, revolving drum type magnets which permit continuous removal of tramp iron from magnet surface are used. Both permanent magnets and electromagnets can be used. Permanent magnets have the advantage of being practically maintenance-free. Furthermore, they do not consume electrical power. Since the beans may become re-contaminated with stray iron (loose nuts and bolts, nails etc.) as they pass through the machinery, magnetic cleaning is not a one-time operation but must be repeated several times along the line. It is therefore advisable to install magnetic separators at the entrance of each machine where the presence of metal particles may cause serious damage (cracking mills, flaking machines etc.)
Stones, sand, dust and other foreign materials are usually removed by conventional seed cleaners. Typically, the seed cleaner consists of a two-deck vibrating screen. The upper screen retains the stones and other coarse materials but allows whole soybeans to fall through. The lower screen retains the soybeans but lets finer particles such as sand to pass through. Light trash, free hull particles and dust are removed by aspiration and trapped in cyclones.
d – Classification: The purpose of this operation is to separate split beans from whole beans. This step is optional and it is applied only if the meal is to be processed for human consumption. Classification is carried out by a simple sifting operation.
e – Cracking: The purpose of this operation is to break the seeds into smaller particles in preparation for flaking. If the beans have been dried to 10% moisture and tempered as described above, cracking also loosens the hulls and permits their separation by aspiration. Ideally, the seeds should be broken to 4 to 6 pieces of fairly uniform size. Production of fines should be minimized. Cracking machines consist of pairs of counter-rotating, corrugated rolls. One roll in each pair rotates faster than the other, to provide the shearing effect necessary to break the seed. Roll diameter is in the order of 25 cm. Roll length depends on the capacity. Two or three pairs of rolls are provided, mounted one on top of the other. A vibrating conveyor secures feeding of the mill at a uniform rate. The corrugations on the upper pair of rolls are coarser and deeper than those on the lower pairs.
A vibrating screen is provided at the exit from the mill. This is where the stream of broken particles is separated into hulls (removed by aspiration for further processing), oversize particles (returned to the cracking mill), meats of the correct size (sent to conditioning and flaking) and fines (usually mixed with the meats for conditioning).
The surface of cracking rolls is subject to considerable wear. After a certain service period, it may be necessary to renew the corrugations (refluting). Good quality rolls may be refluted several times before it becomes necessary to replace them.
f – Conditioning: The purpose of this operation is to increase the plasticity of the meats, in preparation for flaking. The conditioner is similar to the cooker described in connection with expellers. It can be a horizontal screw conveyor type heated reactor or a vertical stacked cooker. Heat can be provided by indirect steam or by direct steam injection, the latter being used to increase the moisture content when necessary. The meats are heated to 65-70oC and the moisture content is brought to 10.5-11%. At this point the plasticity of the meats is such that they can be flattened by pressure in the flaker, without breaking.
g – Flaking: Flaking machines consist of a pair of horizontal counter-rotating smooth steel rolls. Typical roll sizes are in the range of 60-80 cm. in diameter. The rolls are pressed one against the other by means of heavy springs or by controlled hydraulic systems. Conditioned soybean cotyledon particles are fed between the rolls and they are flattened as the rolls rotate one against the other. The roll-to-roll pressure can be regulated and it determines the average thickness of the flakes. The main purpose of flaking is to increase the contact surface between the oilseed tissues and the solvent and to reduce the distance that the solvent and the extract will have to travel in the process of extraction. It is also believed that flaking disrupts the oilseed cells to some degree and thus makes the oil droplets more available for solvent extraction. Typical values for flake thickness are in the range of 0.2 to 0.35 millimetres.
Flaking rolls require maintenance as they wear considerably. To maintain the smoothness of the surfaces and to secure good contact between the rolls at every point, the rolls are reground from time to time. This requires expertise and accurate machines. In order to compensate for uneven thermal expansion, the rolls are manufactured not as perfect cylinders but with a slightly curved profile, thinner at both ends and thicker in the middle. Furthermore, the wear is usually not uniformly distributed and tends to be more extensive at the middle. Some manufacturers supply grinding devices which allow the roll ends to be reground without removal of the rolls.
h: Alternative processes:The processes described above are conventional oil-mill operations. Recently, improved processes have been suggested for individual steps or for the whole seed preparation line.
The ” Hot Dehulling (Popping) System “, offered by Buhler-Miag Ltd. makes use of a “shock treatment” to loosen the hulls.
Soybeans with a moisture content of about 13% are preheated to 60oC, then contacted with a stream of hot air in a fluidized bed unit. This treatment causes popping of the hull. Now the seeds are split in half by impact and the hulls are separated by air. The dehulled split beans are further cracked and flaked. The main advantage of the process is its lower energy consumption since the multiple heating and cooling, drying and humidification steps of conventional dehulling are obviated. The short duration of the heat treatment step prevents extensive protein denaturation. The reduction in NSI (Nitrogen Solubility Index) is claimed to be essentially the same as in conventional dehulled flake preparation. A process flow diagram for the Hot Dehulling System is given below.
The “Alcon Process” offered by Lurgi GmbH, consists of a series of operations installed between the conventional preparation line (right after the flaking mill) and the extractor. The flakes are humidified and heated in a conditioner, maintained at the desired moisture content and temperature for 15-20 minutes (tempering), then dried and cooled before being led to the extractor. This is, essentially, an agglomeration process, whereby the flakes are fused into more compact, porous granules. The following benefits are claimed:
a: The bulk density of the modified granules is by 50% higher than that of the original flakes (550 against 360 kg/m3). This results in a corresponding increase in extractor capacity.
b: The rate of percolation of micella or solvent through the granules is tripled. This results in improved extractor efficiency (see below).
c: Solvent retention in the spent granules is about 25%, while conventional spent flakes may retain as much as 35% solvent. As a result, desolventizer capacity is increased, oil yield is improved and energy is saved.
d: During preparation and extraction, certain enzymes reduce the hydratability of the phospholipids. The thermal treatment associated with the Alcon process inactivates these enzymes and improves the efficiency and yield of the oil degumming process.
e: Due to the thermal treatment mentioned above, meal toasting requirements are less severe.
In the Pellet method suggested by the FRENCH Oil Mill Machinery Company, the crushed material is extruded as pellets. The extruder which is called “the Enhanser Press”, is equipped with special ports for the injection of steam or water into the barrel. The mass is pressed through the holes on a die plate, expands as a result of the sudden evaporation of water and yields firm pellets with sufficient internal porosity but a bulk density higher than that of flakes. The advantages claimed are essentially the same as those of the other agglomeration processes.
A drawing showing the FRENCH Enhancer Press is given in the figure below.
3-2-4 Solvent extraction:
a – Basic principles of solvent extraction:The extraction of oil from oilseeds by means of non-polar solvents is, basically, a process of solid-liquid extraction. The transfer of oil from the solid to the surrounding oil-solvent solution (micella) may be divided into three steps:
* diffusion of the solvent into the solid * dissolution of the oil droplets in the solvent * diffusion of the oil from the solid particle to the surrounding liquid.
Due to the very high solubility of the oil in the commonly used solvents, the step of dissolution is not a rate limiting factor. The driving force in the diffusional processes is, obviously, the gradient of oil concentration in the direction of diffusion. Due to the relative inertness of the non-oil constituents of the oilseed, equilibrium is reached when the concentration of oil in the micella within the pores of the solid is equal to the concentration of oil in the free micella, outside the solid. These considerations lead to a number of practical conclusions:
* Since the rate-limiting process is diffusion, much can be gained by reducing the size of the solid particle. Yet, the raw material cannot be ground to a fine powder, because this would impair the flow of solvent around the particles and would make the separation of the micella from the spent solid extremely difficult. Instead, the oilseeds are rolled into thin flakes, as described in the previous paragraph, thus reducing one dimension to facilitate diffusion, without impairing too much the flow of solvent through the solid bed or contaminating the micella with an excessive quantity of fine solid particles. The effect of flake thickness on the efficiency of solvent extraction is demonstrated in the figure below.
* The rate of extraction can be increased considerably by increasing the temperature in the extractor. Higher temperature means higher solubility of the oil, higher diffusion coefficients and lower micella viscosity. In fact, it is customary to heat the solvent and the intermediate micella to the highest temperature which would still provide an acceptable level of safety.
* An open, porous structure of the solid material is preferable, because such a structure facilitates diffusion as well as percolation. A number of processes have been proposed for increasing the porosity of oilseeds before solvent extraction (See para. 3-2-3-h ).
* Although most of the resistance to mass transfer lies within the solid, the rate of extraction can be increased somewhat by providing agitation and free flow in the liquid phase around the solid particles. Too much agitation is to be avoided, in order to prevent extensive disintegration of the flakes.
* Since the concentration gradient is the factor responsible for moving the oil out of the solid, it is important to keep this gradient high, at each point within the extractor. This effect is obtained most economically by the principle of counter-current multistage extraction. The process is divided to a number of contact stages . Each stage comprises means for mixing the solid and the solvent phases and for separating the two streams after extraction has been achieved. In going from one stage to the next, the flakes and the solvent move in opposite directions. Thus, flakes with the lowest oil content are contacted with the leanest solvent, resulting in high oil yield and high driving force throughout the extractor. The principle of counter-current extraction is shown in Fig.15.
A detailed discussion of the theoretical basis for the design of multistage solid-liquid extraction processes is beyond the scope of the present work. We shall outline here only its principal practical consequences, as far as they provide useful criteria for the selection and operation of an extractor.
Two different methods can be used to bring the solvent to intimate contact with the oilseed material: percolation and flooding. In the percolation method, the solvent trickles through a thick bed of flakes without filling the void space completely. A film of solvent flows rather rapidly over the surface of the solid particles and efficiently removes the oil which has diffused from the inside to the surface. This mode of contact is preferable whenever the resistance to diffusion inside the flake is relatively low (thin flakes with large surface area, open tissue structure). In the flooding mode the solid particles are totally immersed in a slowly moving, continuous phase of solvent. Immersion works better with materials offering a greater internal resistance to oil transfer (thick particles, dense tissue structure).
The number of contact stages necessary to perform a given extraction operation depend on the following variables:
* Flakes/solvent ratio: If the quantity of solvent used to extract oil from one ton of flakes is increased, a smaller number of contact stages will be needed to achieve a given extraction job. However, the full micella resulting from the process would be less concentrated in oil, meaning that we would have to evaporate larger quantities of solvent for each ton of product, and hence, spend more on energy.
* Oil yield: If the number of stages is increased while all other variables are kept unchanged, the proportion of oil left in the spent flakes will be lower and therefore, the oil yield will be higher. The relationship between the number of stages and residual oil in the meal is shown in the figure below.
* Percolation: The quantity of solvent or micella retained within the capillaries and pores of the solid after drainage is called “bound extract” or “bound solvent”. This quantity depends on the properties of the flakes and solvent as well as the drainage conditions. Easy percolation of the solvent through the solid bed leaves less extract in the capillaries after drainage and results therefore, in a reduction of the number of contact stages needed. Proper preparation and handling of the flakes are important to ensure high percolation rate.
b- Choice of solvents:
An ideal solvent for the extraction of oil from soybeans should possess the following properties:
* Good solubility of the oil. * Poor solubility of non-oil components. * High volatility (i.e. low boiling point), so that complete removal of the solvent from the micella and the meal by evaporation is feasible and easy. * Yet, the boiling point should not be too low, so that extraction can be carried out at a somewhat high temperature to facilitate mass transfer. * Low viscosity. * Low latent heat of evaporation, so that less energy is needed for solvent recovery. * Low specific heat, so that less energy is needed for keeping the solvent ant the micella warm. * The solvent should be chemically inert to oil and other components of the soybean. * Absolute absence of toxicity and carcinogenicity, for the solvent and its residues. * Non-inflammable, non-explosive. * Non-corrosive * Commercial availability in large quantities and low cost.
Unfortunately, the ideal solvent possessing all these properties does not exist. Most of the requirements, with the notable exception of flammability and explosiveness, are met by low-boiling hydrocarbon fractions obtained from petroleum. A typical commercial solvent for oil extraction would have a boiling point range (distillation range) of 65 to 70oC and would consist mainly of six-carbon alkanes, hence the name “hexane“by which these solvents are commonly known in the U.S.A.. “Hexane ” solvents for the extraction of edible oil must comply with strict quality specifications. The quality parameters which make up the specifications usually include: boiling (distillation) range, maximum non-volatile residue, flash point,maximum sulphur, maximum cyclic hydrocarbons, colour and specific gravity.
The main shortcoming of light hydrocarbon solvents is their flammability and the explosiveness of mixtures of their vapours and air. Safety considerations gave led to the enforcement of special standards for buildings and installations in solvent extraction plants. All the electrical installations have to be explosion-proof. The discharge end of all vents have to be equipped with refrigerated condensers to minimize escape of solvent vapours to the atmosphere. Very strict safety measures are taken to prevent the hazard of sparks in and around the plant. All these add to the high cost of erection and operation of solvent extraction plants.Even so, accidents are not uncommon.
The continuous search for alternative solvents is, therefore understandable. One such solvent, trichloroethylene, was in commercial use for a short period in the early 1940’s, but had to be abandoned when it was discovered that the meal prepared in this way was toxic to animals. Another alternative approach makes use of “supercritical extraction” with liquid carbon dioxide under high pressure. Although technically feasible, supercritical extraction of soybean oil is not commercially viable at present, due to the high cost of the equipment and the relatively poor oil dissolving capacity of carbon dioxide near its critical point. Alcohols constitute yet another class of potential solvents for oil extraction. Water-free (absolute) low aliphatic alcohols such as ethanol and isopropanol are fairly good solvents for oils at high temperature but the solubility of oils in these solvents decreases drastically as the temperature is lowered. This high dependence of solubility on temperature is precisely the principle on which alcohol extraction processes are based. Extraction takes place at high temperature. The micella is then cooled. Saturation occurs and excess oil separates as a distinct phase which can be recovered by centrifugation. The solvent is reheated and sent back to the extractor. These alcohols are less flammable then hexane, but precautions are still necessary. Despite considerable research efforts to develop alternative solvent systems, extraction with light hydrocarbons continues to be, practically, the only commercial solvent extraction process for soybean oil.
c- Types of extractors:
Solvent extractors are of three types: batch, semi-continuous and continuous.
In batch processes, a certain quantity of flakes is contacted with a certain volume of fresh solvent. The micella is drained off, distilled and the solvent is recirculated through the extractor until the residual oil content in the batch of flakes is reduced to the desired level. Batch extractors as industrial units are now obsolete. Laboratory and pilot plant size extractors are still used for experimentation and instruction purposes.
Semi-continuous systems consist of several batch extractors connected in series. The solvent or micella flows from one extractor to the next one in the series. The material in the first extractor is the most exhausted, since it has been treated with fresh solvent. After a while, the second extractor is made “head” of the series and connected to the fresh solvent line. The spent flakes are discharged from the first extractor, which is then filled with a batch of fresh flakes and is connected to the system as the “tail” unit, and so on.
Semi-continuous systems of the type described above are seldom used for the solvent extraction of soybeans. However, the same principle is applied in one of the widely known solvent extraction systems for other oilseeds: the FRENCH Stationary Basket Extractor.
The FRENCH extractor is essentially a vertical cylindrical vessel, divided into a number of tall vertical sections or “baskets” by radial walls. The baskets are stationary. Solvent or micella is fed at the top of the basket and percolates through the deep bed of solids. Using a system of moving micella showers, the oilseed material is contacted with micella at decreasing oil content, and finally with fresh solvent, thus achieving countercurrent extraction, without moving the solid bed. In its recent version, the FRENCH stationary basket extractor is equipped with a rotating basket bottom, to achieve automatic discharge of the baskets at the correct time and to render the extractor nearly continuous. The capacities of units supplied since 1975 for soybean oil extraction, range from 100 to 3000 tons per day.
In continuous extraction, both the oilseeds and the solvent are fed into the extractor continuously. The different available types are characterized by their geometrical configuration and the method by which solids and solvents are moved one in relation to the other, in counter-current fashion. The most prominent types will be described in the next paragraphs.
* Belt extractors_the DE SMET extractor: This extractor, offered by the Belgian De Smet Company and its subsidiaries in many countries, was developed in 1946 by J.A. De Smet at the “Nouvelles Huileries Anversoises” oil mill in Belgium. According to the company, since then over 450 plants using the DE SMET process have been built in various parts of the world.
A drawing describing the DE SMET Extractor is given in the figure below. The extractor consists of a horizontal, sealed vessel in which a slowly moving screen belt is installed. Flaked soybeans are fed on the belt by means of a feeding hopper. A damper attached to the hopper outlet acts as a feed regulating valve and maintains the solids bed on the belt at constant height. This height can be adjusted according to the expected rate of percolation of the micella through the bed. Difficult percolation is compensated for by lowering bed height. For properly flaked soybeans, the height of the flake bed at the head end of the extractor is normally 6 to 8 feet (180 to 240 cm.). The throughput rate of the extractor is adjusted by changing the belt speed. There are no dividing baffles on the belt and the solid bed is one continuous mass. Yet the extractor is divided to distinct extraction stages by the way in which the micella stream is advanced. The solvent is introduced at the spent flake discharge end ( i.e. at the end opposite to the flake feeding side of the extractor ). It is sprayed on the flakes, percolates through the bed, giving the spent flakes a last wash and removing some oil. The resulting dilute micella is collected in a sectional hopper underneath the belt, from which it is pumped and sprayed again on the flakes at the next section in the direction opposite to belt movement. This process of micella collection, pumping and spraying at the next section is repeated until the micella leaves the hopper at the head-end of the extractor, carrying the highest concentration of oil (heavy micella). The screen is washed with heavy micella at the head-end, just before the entrance of fresh flakes, and then again with fresh solvent, right after the discharge of spent flakes.Washing of the screen is essential to prevent clogging. Washing with full micella at the feed-end provides surface lubrication and prevents adhesion of the flakes to the surface of the screen. The entire extractor vessel is maintained at a slight negative pressure so as to prevent leakage of solvent vapours to the atmosphere.
According to the manufacturers, DE SMET extraction plants have been built for capacities ranging from 25 to 3000 tons of raw material per day. Solvent losses are 0.07% to 0.3% and the residual oil content of the extracted material is 0.25% to 0.6%.
* Moving basket extractors: In this class of extractors, the flakes do not constitute a continuous mass but are filled into separate, delimited elements (baskets) with perforated bottoms for draining. The baskets can be moved vertically (bucket elevator extractors), horizontally ( frame belt and sliding cell extractors), or can be rotated around a vertical axis (carrousel extractors). Vertical bucket-chain extractors are among the first industrial solvent extractors constructed for continuous operation. Many are still in operation but they are less frequently found in more recent installations.
In the horizontal moving basket extractors manufactured by the LURGI Company, the “basket” or “cell” is formed by an endless bucket belt and a separate perforated bottom. The bottom can be fixed perforated plates on which the bucket separations slide (sliding cell design) or screen belt conveyors moving with the buckets. Both types are shown below.
Another type of horizontal basket extractor, featuring tilting baskets or trays, is manufactured by the HLS Company Ltd. The operation principle of the T.O.M. (Turning Over of Material) HLS extractor is shown in Fig.20. Each basket in the extractor can be flooded, permitting immersion and percolation in the same extractor. In order to overcome the problem of the formation of a dense surface layer of compressed fines, the trays or baskets are inverted at the end of the conveying chain. The material falls to the basket or tray below. The impermeable surface layer is broken and the oilseed material undergoes mixing in the process of its transfer from one level to the other. Extraction continues as the material moves, in reversed direction, on the lower (return) side of the conveyor. Thus, unlike most horizontal extractors, in the HLS Extractor the inlet for fresh raw material and the outlet for the spent flakes are on the same end of the shell.
* Carrousel extractorssomewhat resemble the cylindrical FRENCH extractor described above, but here, the “baskets” rotate around the axis of the cylinder while the solvent/micella circuitry is fixed. The construction principle of the Carrousel Extractor, manufactured by EXTRACTIONSTECHNIK GmbH, is shown in below. The following description of the extractor and its operation is from an article by Dr. Ing. Wolfgang Kehse:
” The extractor consists of a single-part rotor with an inner and outer cylindrical wall. The ring-shape interspace is divided by radially arranged conical partition walls into a number of chambers (10 to 20) . It is slowly rotated usually by chain drive, the larger gear rim of which is placed round the rotor. Smaller extractors may be directly driven by a central shaft. These rotation speeds vary from one rotation in 20 minutes up to one rotation in 4 to 5 hours, and are adjustable. The rotor rotates above a slitted bottom with only a few millimetres’ gap. This slitted bottom is constructed of profiled rods with a trapezoidal cross-section. This profile causes the slits which are at their surface about 0.8 mm wide to become wider further down. The specific advantage of this slitted bottom, however, is that the slits are exactly concentric with the rotor shaft. The raw material is filled into the chambers and thus form a compact layer which can reach a height of from 0.5 to 2.5 meters, depending on the material to be extracted. The height of the rotor corresponds to this. Therefore, a free space of about 200 mm above the layer remains, which is filled with liquid solvent during the time that the chamber is being sprayed with solvent.
Depending on the required time for extraction, the material is moved at a speed of 1-10 mm/sec., over the concentric slits in the bottom. Because the slits are arranged parallel to the direction of movement of the material, no mechanical forces apart from the sliding resistance are exerted on the extraction material and subsequently no plugging of the slits can occur. While moving over the slitted bottom, the bed of material is percolated by micella of different concentrations, beginning with the end-micella having the highest concentration immediately after feeding of the solid material up to the pure solvent at the end of its passage. The micella passes through the bed of material and the slitted bottom and is the collected in chambers separated by weirs in the lower part of the extractor. From there it is pumped back onto the bed of material. The discharge of the extracted solid material is effected through the slitted bottom by a hole as wide as a rotor chamber and allowing the contents to drop down into a discharge chute where it is moved on for further processing by a screw conveyor. The partition walls of the chambers are conically widening downward so that any sticking of the chamber contents is impossible.”
According to the manufacturer, Carrousel Extractors are available in capacities from 20 up to 4000 tons per 24 hours. The largest extractor (4000 tpd.) has a nominal diameter of 15 m.
3-2-5 Post-extraction operations
Two streams leave the solvent extraction stage: an oil-rich fluid extract (full micella) and solvent-laden spent flakes. The next operations have the objective of removing and recovering the solvent from each one the two streams.
a: Micella distillation:Full micella contains typically 30% oil. Thus, for every ton of crude oil some 2.5 tons of solvent must be removed by distillation. Most manufacturers of solvent extractors also offer micella distillation systems. The characteristics of a good micella distillation system are: good energy economy, minimal heat damage to the crude oil and its components, minimal solvent losses , efficient removal of the last traces of solvent from the oil and, of course, good operation safety. The modes of solvent vaporization include flash evaporation, vacuum distillation and steam stripping.
b: Meal desolventizing:The spent flakes carry with them about 35% solvent. The removal and recovery of this portion of the solvent is also one of the most critical operations in oil mill practice, since it determines, to a large extent, the quality of the meal and its derivatives.
In desolventizing-toasting (DT) applied in the production of soybean oil meal for animal feeding, the time-temperature-moisture profile of the process permits, in addition to solvent removal, a heat treatment sufficient to inactivate the undesirable enzymes and inhibitors and to improve the palatability of the meal to animals (toasting). The most common type of desolventizer-toaster consists of a vertical cylindrical stack of compartments or “pans”. Each compartment is fitted with stirrers or racks attached to a central vertical shaft. Spent flakes are fed at the top of the desolventizer-toaster. The pan floors are equipped with adjustable-speed rotating valve, to permit downward movement of the material , through the pans, at the desirable rate. Two methods of heating are used: direct steam heating and indirect steam heating. For heating with indirect steam, the pans are equipped with double bottoms acting as steam jackets. For direct steam heating, hot live steam is injected into the mass through spargers. The rotating stirrers spread the material and provide the necessary mixing action. Direct steam is used for three reasons:
* The transfer of heat from the heated surface of the pan floor to the oilseed material is slow and difficult, especially after a considerable proportion of the solvent has been removed and no fluid medium is available for heat transfer. In this case, direct contact between the solid material and condensing steam is a more efficient method of heating. Condensation of the steam adds moisture to the flakes.
* The added moisture facilitates the protein denaturation reactions leading to the inactivation of trypsin inhibitor. It is also believed that the toasting effect accomplished by the combined action of heat and moisture enhances the palatability of the meal to animals.
* The steam distillation effect is necessary in order to remove last traces of solvent from the meal.
The various models of vertical stack type DT’s differ in the sequence of direct/indirect heating zones and several other features. In the FRENCH DT shown below, the top pans are indirect steam heated. They constitute the pre-desolventizing zone. The bottom pans are direct steam heated and they serve as the toasting/stripping zone. The meal coming out of this DT has about 18% moisture and a temperature of about 105oC. It has to be dried and cooled. A separate dryer/cooler (DC) is used for this purpose (see below).
The DE SMET DT shown in below has 4 to 10 pans with steam-heated bottoms. The apparatus is maintained at a slight negative pressure.
The meal dryer-cooler (DC) is similar to the DT in construction but much shorter. Ambient air is used to dry and cool the meal before storage or bagging. The construction of a self-standing DC unit, offered by FRENCH, is shown below.
The DT and DC units can also be combined into one piece of equipment. Most manufacturers of desolventizing equipment also offer combined DTDC units. The operating principle of such a system, sold by LURGI is shown below.
A photograph of a 1200 ton per day desolventizer-toaster-dryer is given in below.
While desolventizing-toasting is the standard method for the manufacture of soybean oil meal for animal feeding, this process is not suitable for the production of “white flakes”, i.e. meal with minimum protein denaturation. As it can be seen below, protein denaturation ( expressed as the reduction in Nitrogen Solubility Index, NSI) by treatment with live steam is very rapid. White flakes, which are the starting material for the production of soybean protein isolates, most concentrates and texturized products, must have a high NSI value.
The best method of desolventizing for the production of white flakes is flash desolventizing (FD). In this process, the solvent laden spent flakes coming out from the extractor are fluidized in a stream of superheated solvent vapours. The superheat of the vapour provides the energy for the evaporation of solvent from the flakes. The turbulent nature of the flake-vapour flow permits extremely rap[id heat and mass transfer. Protein denaturation is minimized, mainly because of the short heating time. A short stripping stage may be necessary to complete solvent removal and rapid cooling is a must for preventing undue reduction of NDI. The flow-diagram of a flash desolventizing system is shown below.
4. EDIBLE SOYBEAN FLOURS AND GRITS
4.1 Introduction
Flours and grits are the simplest of all edible soybean protein products. The extent of processing which goes into their production is minimal. The cost of extra processing, starting with the dehulled clean beans (for full-fat flour) or with dehulled white flakes (for defatted flour), has been estimated at 60 to 100 U.S.$ per ton. The total cost of the product, in the bag, at the production site, would then be less than $400 per ton. Recently (January 1991) a leading supplier in the U.S. has quoted soybean flour at $14.00/cwt. ( approximately $308 per metric ton), ex-factory. This makes soybean flour one of the most economical sources of edible protein. Speciality flours, produced in smaller quantities, may be more expensive.
The annual production of edible soybean flours and grits increased from some 60,000 tons in 1960 to about 2,000,000 tons today.
The production of edible soybean flours and grits may take place either as an independent industrial activity or as a natural sequel of oil-mill operations. In fact, many oil-mills, recently erected in various parts of the world, feature production lines or departments for edible products, in addition to the usual oil and meal lines. The principal differences between processing for meal and processing for edible flour are in the quality of the raw material, the need for dehulling and the more rigorous control of the sanitary conditions of the plant and the process. Frequently, oil-mill operators prefer to produce only edible products or only meal, in alternate fashion rather than simultaneously.
4.2 Defintions, composition and quality parameters
4-2-1 Definition and classification of edible soy flours and grits
Soy flours are products obtained by finely grinding full-fat dehulled soybeans or defatted flakes made from dehulled soybeans. To be called soy flour, at least 97% of the product must pass through a 100-mesh standard screen. (A 100-mesh screen has 100 openings per inch.)
Soy grits have essentially the same composition as flour, but coarser granulation. They are usually classified into three groups, according to particle size:
Coarse 10 to 20 mesh Medium 20 to 40 mesh Fine 40 to 80 mesh
Circle and Smith (1972) have pointed out that the name soy flour may be misleading, since its composition is totally different from that of the popular product commonly known as flour, i.e. wheat flour. They suggested alternative names such as “defatted soy solids” (as non-fat milk solids) or “soy powder” or “soy pulverate”.
Edible soy flours are made from dehulled beans, hence their relatively low crude fibre and high protein content.
Soy flours (or grits) are classified according to their lipid content as follows:
* Defatted soy flour, obtained from solvent extracted flakes, contains less than 1% oil.
* Full-fat soy flour, made from unextracted,dehulled beans, contains about 18% to 20% oil.
* Low fat soy flour, made by adding back some oil to defatted soy flour. Lipid content varies according to specifications, usually between 4.5% and 9%.The most common range is between 5% and 6%.
* High fat soy flour, produced by adding back soybean oil to defatted flour, usually at the level of 15%.
* Lecithinated soy flour, made by adding soybean lecithin to defatted, low fat or high fat soy flours in order to increase their dispersibility and impart emulsifying properties.. Lecithin content varies according to specifications, usually up to 15%.
Commercial soy flours and grits are further classified according to their Nitrogen Solubility Index (NSI), or their Nitrogen Dispersibility Index (NDI). It will be recalled that these parameters indicate the extent of protein denaturation and hence the intensity of heat treatment which has been applied to the starting material. Flours made from “white flakes” have NSI values of about 80%, while those made from toasted flakes show NSI levels of 10 to 20%. Other grades are available over the entire range of intermediate NSI values.The specification of a specific value of NSI reflects , in fact, a compromise between the need to maintain the functional properties of the soy proteins or some enzyme activity, and the desire to inactivate anti-nutritional factors and eliminate the beany taste, all in function of the end use.
4-2-2 Composition
The typical composition of different types of soy flours is given in Table 4-1. The basic composition of soybeans is added for comparison. Since the moisture content of the products may vary during storage, the percentage figures for protein, fat, fibre and ash are given on a moisture-free basis. A typical level of moisture content is also shown.
4-2-3 Quality standards
In addition to the identity standards and definitions mentioned above, quality standards have been formulated by official agencies (e.g. FAO/WHO/UNICEF Protein Advisory Group). Trade specifications usually exceed the official standards. The quality parameters which constitute a specification usually include:
a- Composition:
Protein
a minimum value
Fat
a maximum value for defatted flour a range for others
Lecithin
a range for lecithinated flours
Crude fibre
a maximum value
Ash
a maximum value
Moisture
a maximum value
b- Physical parameters:
Granulation
as mesh number or particle size distribution.
c- Microbiology:
Total plate count
a maximum value
Coliforms
a maximum value
Salmonella
a maximum value (usually 0)
d- Heat treatment history:
Protein solubility
as NSI, NDI, PSI or PDI
Tryps ininhibitor activity
Urease activity
Lipoxidase activity
for enzyme-active flour.
Available lysine
e- Sensory parameters:
Colour
Taste
Odour
f- Defects:
Insect parts
a maximum value or total absence
Foreign material
” ” “
Black specks
” ” “
g- Commercial:
Packaging, delivery etc.
4.3 Full fat soy flour and grits
4-3-1 Production processes
a- Oil-mill related industrial production process: The process for the production of full-fat soy flour and grits as a side line of large scale oil-mill operation is relatively simple. It consists of three major steps: dehulling, heat treatment and milling.
Cleaned, grade A yellow soybeans are dried, tempered, classified to separate split beans, cracked and dehulled by aspiration. These operations are essentially similar to the seed preparation steps of an oil-mill, from raw material silos up to the obtention of dehulled meats, and have been discussed in detail previously (Section 3-2-3, a to e).
The dehulled meats coming out of the vibrating screen are now subjected to humid heat, to achieve the specified product NSI value. This is conveniently done in a vertical conditioner with direct and indirect steam heating sections.
This step is obviously omitted if the final product is to be unheated (enzyme active) flour. The last sections of the conditioner are used to dry the meats to a moisture content below 10%.
The properly conditioned and dried meats are cooled and then finely ground. Hammer mills, pin mills, impact turbo mills and similar pulverizers are used to grind the meats so that not more than 3% of the product will be retained by a 100-mesh screen. In practice , full fat soy flour is difficult to screen on such fine sieves, due to particle agglomeration. Air classification systems which separate the fine product and recirculate the coarse fraction through the mill are more adequate than screen sifters.
b- Alternative processes: In the framework of the efforts to promote direct consumption of soybeans in the less industrialized parts of the world, methods for the preparation of full-fat soybean flour with a minimal amount of processing have been developed. These methods permit production of flours independently of the oil industry.
One such process has been described by Mustakas et al.(1967) In this village scale production method, the soybeans are soaked in water, then cooked in boiling water, air dried, cracked by hand, winnowed to separate the hulls and finally hand ground in a mortar or any other grinding device available.
A more industrialized version of the process (Mustakas et al.(1970) is similar in most aspects to the large scale production process described above, except for the step of heat treatment. In this process the flour is submitted to a continuous high temperature-short time humid heat treatment, using an extruder-cooker. The dehulled meats are first equilibrated with moisture in a direct steam fed conditioner/ tempering bin, then cooked under pressure in a continuous extruder/cooker. The extrudate is cooled and ground as usual. The HTST treatment eliminates the beany flavour and produces a light, open structured flour. A slightly different process, also centred around extrusion cooking, known as the WENGER PROCESS, is available from the Wenger Mixer Manufacturing Co. More recently, low-cost extruders have been made available for the less sophisticated extrusion-cooking applications. “Low-cost” may mean $5,000, compared to $100,000 for a regular extrusion system. Such low-cost extruders have been used for the preparation of full-fat soy flour. According to Lorenz et al.(1980), the total investment needed for a 550 kg./hr plant was (1980) about $120,000 including building and land. The cost of production, including raw materials, packaging materials and overhead was $223 per ton. Extruded full-fat soybean flour was being produced with a low-cost extruder in Mexico in 1980.
In extrusion cooking, the material reaches temperatures in the order of 150oC. At such high temperatures, destruction of urease activity is no longer a credible indicator for the inactivation of trypsin inhibitor, which must be monitored directly.
The BUHLER PROCESS developed by Buhler Co. in Switzerland, is based on very fine grinding and fast heating. The resulting powder has been suggested as an alternative for soymilk solids.
A process, based on pre-germinated beans has been described by Suberbie et al.(1981). The beans are soaked in water for 3 hours and allowed to germinate. At the end of the germination period, the soybeans are steamed, dried to 6% moisture, dehulled and ground in a cooled hammer mill. Germination resulted in flavour and odour improvement. Milling capacity was impaired by germination. Pre-germinated full-fat soybean flour has been produced commercially in Mexico.
4-3-2 Utilization
The principal use of full-fat soybean flour, as well as re-fatted and lecithinated flours, is in the bakery industry. Two types of flour are used: enzyme-active and enzyme-inactive.
Enzyme-active full-fat soybean flour is prepared without heat treatment and has a high NSI value around 80%. It is used in bakery products (white bread and rolls), mainly for its lipoxidase activity. Lipoxidase catalyses oxidative bleaching of the carotenoid pigments in wheat flour. Enzyme-active soybean flour is a valuable “natural” flour bleaching agent, especially where the use of chemical bleaching agents has been prohibited. Lipoxidase activity is also beneficial to the mechanical properties of the dough. Since the soybean product is added in relatively small quantities (up to 0.5% on flour basis in bread and buns in the U.S.A.) the beany flavour of unheated soybeans is not a limiting factor. Usually, enzyme-active full-fat soy flour is not sold as such, but rather in mixtures containing other ingredients such as cornflour.
With the development of successful flash desolventizing systems which permit desolventizing without appreciable enzyme inactivation, defatted enzyme-active flours have largely replaced the full-fat product, especially in the U.S.A.
Enzyme-inactivated (heated) full-fat soybean flours, alone or with re-fatted and lecithinated soy flours, is mainly used in the heavier types of cake batters, such as sponge cake and pound cake. It contributes to the richness of the cake while increasing the proportion of water that can be added to the mix. Due to their oil and phospholipid content, these flours exert egg and shortening sparing effects and act as emulsifiers. In these formulae, soybean flours are used at the level of 3-5%, based on flour weight. Full-fat or lecithinated soy flour with high nitrogen solubility (NSI of 80%) has been found to improve eating quality and reduce fat absorption in doughnuts.
4.4 Defatted soy flours and grits
4-4-1 Production processes
The processes for the manufacture of raw or heated dehulled solvent extracted flakes have been described in section 3.
Usually, all the flakes made for edible products are flash-desolventized, then carefully steam-heated to the desired NSI value.
The final milling is critical and energy-consuming. Although identity standards require milling to 97% minus 100-mesh, specialty flours (such as those used as milk solids replacement in infant formulae) are ground to a finer particle size.
At such levels of fineness, the conventional hammer mill is practically useless. Impact turbo mills or high-speed pin mills have to be used.
4-4-2: Utilization:
a- Use in bakery and other cereal products:
Nutritionally, soybean protein is an excellent complement to lysine-limited cereal protein, hence the basis for the use of soy flour as an economical protein supplement in bread, tortillas, pasta and other cereal products. Supplementation of bread and other cereal staples with defatted soy flour has been promoted in a number of countries, and even enforced in some. The use of defatted soy flour in bread does not create any appreciable technological or quality problems, as long as less than 10% of the wheat flour has been replaced by soy flour. At higher replacement levels, up to 15%, loaf volume and crumb texture may be impaired. Baking quality can be recovered, however, by means of some adjustments such as higher yeast level, use of lecithin and other emulsifying agents etc.
Another bakery related potential use of soy flour in combination with cereals is in the production of the so-called “composite flours.” These are mixtures of flours, starches and other ingredients, supposed to replace wheat flour, totally or partially, in bakery products. Extensive research projects aimed at the development of such flours have been sponsored by international and national development agencies in the last 20 years or so. The main reason for developing composite flours is to relieve the economy of countries where wheat is not grown, from the burden of importing this commodity. Other reasons include the production of alternative baking flours for people who cannot tolerate wheat products (e.g. coeliac disease patients).
Considerable quantities of soy flour (1.5 to 2% on flour weight basis) are used in bakery products, particularly in white bread, as a replacement for nonfat milk solids. In this application, soy flour (and sometimes soy protein concentrate) is used in combination with whey solids. Milk replacer blends, consisting mainly of defatted soy flour, whey solids, caseinates and other nutritional or functional ingredients are available at protein content levels of 20% to 40%.
In many applications, especially in the U.S.A. and Europe, the largest quantity of soy flours is used in bakery products, not for nutritional reasons but rather for their functional characteristics.
Enzyme-active defatted flour is used as a bleaching and dough improving agent as discussed in the previous section dealing with full-fat flours.The characteristics of such a flour (SOYBAR, made by Solbar Hatzor Ltd.), as reported by the manufacturer, are given below, as an example:
Product description: Enzyme active defatted soy flour, derived from high quality, dehulled soybeans. Has a mild flavour and aroma profile and a light cream colour.
Characteristics: Highly dispersible in water. Has excellent water binding properties.
Specifications:
Protein (as is) 50% min.
Moisture
10% max.
Crude fibre
4% max.
Ash
6.5% max.
Fat
1.0% max.
Particle size
95% less than 74 microns
Standard plate count
50,000/g. max.
Salmonella in 200g.
Negative
E. Coli in 1g.
Negative
Packaging: 20 kgs. net weight, in multi-ply, valve-pack, kraft paper bags with polyliner.
Defatted soy flours with 50-75% protein dispersibility are extensively used in bakery products. They increase the water absorption capacity of flours in bread dough and cake batters. In cakes,they improve film forming and even distribution of air cells. As a result, even cake texture and more tender crumb structure are achieved. In hard cookies, soy flour improves machining. In all these products, soy flour is used at the level of 2-5%.
More thoroughly toasted flours and grits are used to impart a pleasant nutty flavour to whole-grain and multi-grain specialty breads.
An important application of defatted soybean flour and grits in combination with cereals is in the production of nutritionally balanced all-purpose food blends, distributed to under-nourished populations or in cases of food shortage emergencies. The best known of these blends are: CMS (corn-milk-soy), developed in the U.S.A. by the Northern Regional Research Centre in cooperation with the American Corn Millers Federation, National Institute of Health and AID, CS (corn-soy) and WS (wheat-soy). More than 1.5 million tons of CMS have been distributed between 1966 and 1979. An “instant” CMS has been also developed. CMS can be used in soups, gruels, porridges etc. typically, CMS contains 17.5% defatted soy flour, 15% non-fat milk solids, about 60% corn. CS contains 22% soy flour and 71% corn. WS has 20% soy, 53% wheat bulgur and 20% wheat protein concentrate. Another well-known blend is INCAPARINA, developed by the Instituto de Nutricion de Centro America y Panama (INCAP), to fight children malnutrition. The oilseed protein source in the original formula of INCAP was cottonseed, but it has been replaced by soybean flour.
b- As a raw material for further processing: White flakes and defatted soy flour with a high protein solubility serve as the starting raw material for the manufacture of most protein concentrates, isolated soy protein and extrusion- texturized soy flour. They are also used, alone or in combination with whole soybeans , as a starting material for the production of soy sauce.
5. SOYBEAN PROTEIN CONCENTRATES (SPC)
5.1 Introduction
Edible soybean protein concentrates are relatively new products. Their availability as commercial products dates from 1959. In the last 30 years or so, these versatile products have become important ingredients, well accepted by many food industries. In many applications, they simply replace soy flours. In others, they have specific functions which cannot be performed by soy flours.
Historically, the need for the development of soybean protein concentrates stemmed primarily from two considerations: to increase protein concentration and to improve flavour.
It is very difficult to avoid the occurrence of the green-beany flavour of soybeans in untoasted full-fat or defatted soy flour, prepared in the conventional way. Beany flavour is one of the major objectionable characteristics, limiting the use of conventional soy flours. One of the objectives of the further processing of flours into concentrates is to extract the particular components which are responsible for the bitterness and beany taste.
As shown in the previous chapter, the maximum level of protein content in soy flour, even after nearly complete removal of hulls and oil, is about 55% (moisture-free basis). In certain applications, such as in meat products, a soybean protein ingredient with a higher percentage of protein is often preferable.
Soybean protein concentrates normally cost 2 to 2.5 times more than defatted soy flour. Considering the relative protein contents of these two products, the cost per unit weight of protein is about 80% higher in the concentrate.
The starting material for the production of soy protein concentrates is dehulled, defatted soybean meal with high protein solubility (white flakes). The concentration of protein is increased by removing most of the soluble non-protein constituents. These constituents are primarily soluble carbohydrates (mono, di and oligosaccharides), but also some low molecular weight nitrogenous substances and minerals. Normally, 750 kilograms of soybean protein concentrate are obtained from one metric ton of defatted soybean flakes.
There are three major methods for extracting these components in a selective manner, without solubilizing the major protein fractions. These are not different methods for manufacturing the same product, but each method produces a different type of concentrate, with distinct characteristics and specific uses. These methods are known as:
*The aqueous alcohol wash process * The acid wash process * Heat denaturation/water wash process
5.2 Defintion, compostion, types
The Association of American Feed Control Officials, Inc. (AAFCO), specifies soy protein concentrates as follows:
” 84.12: Soy Protein Concentrate is prepared from high-quality sound, clean, dehulled soybean seeds by removing most of the oil and water-soluble non-protein constituents and must contain not less than 70% protein on a moisture-free basis.” ( from the ’89 Soya Bluebook.)
Following is the composition of a typical food-grade soy protein concentrate ( SOLCON, made by Solbar Hatzor Ltd.) as specified by the manufacturer:
Protein (mfb) .
70% min.
Moisture
8% max.
Crude fibre
4.5% max.
Ash
7% max
Particle size
95 % < 150 microns
Fat
1% max
Standard plate count
15,000/g. max
Salmonella in 200 g.
Negative
E. Coli in 1 g
Negative
As explained above, there are three basic types of soy protein concentrates, distinguished according to the method used for extraction of the non-protein solubles. All three types have basically the following proximate composition, on a moisture-free basis:
Protein (Nx6.25)
70%
Insoluble carbohydrates
20%
Ash
5%to 8%
Lipids
1%
Soy protein concentrates are further characterized by their protein solubility index. Soy proteins are rendered insoluble by each of the three extraction processes. However, it is possible to increase the solubility of the protein in the concentrate by further processing, for example by neutralization of acid-washed concentrate with alkali. Concentrates made by heat denaturation/water leaching processes are irreversibly denatured and darker in colour. Alcohol-wash concentrate has a low NSI value (10 to 15%) due to denaturation of the protein by the aqueous alcohol. The molecular changes in the proteins caused by alcohols are, however, different from those resulting from heat denaturation. Thus, alcohol-wash concentrate retains most of the functional properties (slurry viscosity, emulsification power etc.) despite its low protein solubility as determined by the standard NSI or NDI tests.
The dispersibility and functionality of alcohol-wash concentrates can be increased by steam injection or jet-cooking and improved further by high-shear homogenization. (Soy Protein Council 1987).
Much of the characteristic beany flavour is also usually removed by the extraction process. Soybean protein concentrates are relatively bland. The flatus-producing oligosaccharides of soybean flour, raffinose and stachyose, are also efficiently removed by the solvents used in the production of concentrates.
Soy protein concentrates are marketed in various forms: granular, flour and spray dried. In addition, texturized concentrates are also available. These texturized products will be discussed later.
Since some low molecular weight proteins are also extracted along with the sugars, the amino acid composition of the concentrates may differ slightly from that of the original flour. (Table 5-1).
Table 5.1 Amino acid composition of SCP and soy flour (grams per 16g. nitrogen)
5.3 Production processes
5-3-1 The aqueous alcohol wash process
The process is based on the ability of aqueous solutions of lower aliphatic alcohols (methanol, ethanol and isopropyl alcohol) to extract the soluble sugar fraction of defatted soy flour without solubilizing its proteins. The optimal concentration of alcohol for this process is about 60% by weight.
The theory of solvent extraction (see para. 3-2-4) is applicable to the extraction of defatted soy flour with aqueous alcohol.
Starting with defatted white flakes as raw material, the process consists of the following steps: Liquid-solid extraction, removal and recovery of the solvent from the liquid extract, removal and recovery of the solvent from the extracted flakes, drying and grinding of the flakes.
a- Solid-liquid extraction: This can be carried out batchwise or continuously. Continuous extraction is justified for relatively large scale operations. According to Campbell et al.(1985), continuous processes are employed for plants with typical capacities over 5,000 tons per year. Unlike oilseed crushing industries, smaller plants are not uncommon in this branch. The batch process is, therefore, rather widely applied. The methods and types of equipment used are essentially similar to those encountered in oil extraction plants: horizontal belt and basket extractors, stationary and rotary cell extractors etc. In the case of alcohol extraction, the solvents are quite volatile and flammable. Adequate precautions for the prevention of fire and explosion are necessary.
The reason for using high-NSI white flakes as the starting material is not necessarily related to the objective of obtaining a product with high protein solubility.( As explained above, this would not help anyhow , due to the different type of protein denaturation caused by the alcohol.) The principal reason for preferring this type of raw material is due to the fact that the percentage of extractable soluble sugars in white flakes is higher than in toasted meal. Toasting renders the sugars less soluble by binding them to proteins (Maillard reaction) or by caramelization. As a result of this type of condensation reactions, the sugars are no longer extractable by the solvent and they remain in the product, lowering the protein concentration in it. Furthermore, the darker colour of concentrates made from overheated meal is also objectionable, and their nutritional value is lower (lower lysine availability.)
b- Removal and recovery of the solvent from the liquid extract: The alcohols are removed from the liquid extract by evaporation and rectified by distillation. They are then brought to the proper concentration and recycled through the extractor. The distillation residue is an aqueous solution of the sugars and other solubles. It is concentrated to the consistency of honey and sold as “soy molasses”. Typically, soy molasses contain 50% total soluble solids. These solids consist of carbohydrates (60%), proteins and other nitrogenous substances (10%), minerals (10%), fats and lipoids (20%). It is mainly used as a caloric ingredient and as a binding agent in animal feeds.
c- Desolventizingthe solids: After extraction, the solvent saturated flakes are desolventized . The methods are essentially the same as for the removal of hexane from soybean meal flakes. Flash desolventizing, using superheated vapours of the alcohol-water mixture can be applied to protein concentrates. Any excess water left in the flakes after desolventizing is removed by hot air drying.
d- Grinding: The methods and equipment used to grind soy protein concentrate flakes are essentially the same as those employed in the production of soy flours (see Section 4-3-1).
5-3-2 The acid-wash process
This process is based on the pH-dependence of the solubility of soybean proteins, discussed in Section 1-6-2. It will be recalled that the majority of soybean proteins exhibit minimum solubility at pH 4.2 to 4.5 (isoelectric region). Therefore, it is possible to extract the sugars, without solubilizing the majority of the proteins, using, as a solvent, water to which an acid has been added so as to keep the pH at the isoelectric region.
The acid-wash process has the obvious advantage of using a non-flammable, non-explosive, non-toxic and inexpensive solvent: water. To a certain extent, this is also the disadvantage of the process. Separation of the solid from the solvent is more difficult and less complete, due to the fact that the flakes absorb considerable quantities of water and swell. Gravity draining is not suitable for efficient solid-extract separation. Rotary vacuum filters or decanting centrifuges must be used instead.
A batch process using horizontal decanting centrifuges is shown in Fig. 29. Defatted soy flakes or flour are mixed with acidified water in an agitated vessel. The slurry is then fed to the decanter centrifuge which separates the extracted solids from the extract (whey). The solids are discharged continuously at approximately 30% dry matter content. The solids can be dried at this stage, to yield an “isoelectric” concentrate of low protein solubility. If a more functionally active, neutral concentrate is desired, the isoelectric solid cake is resuspended in water and the acidity is neutralized. A second step of centrifugal separation gives a cake of neutral concentrate with a protein content of 75% on dry matter basis. This cake also retains about 70% water, by weight.
The cake is usually wet-milled to a fine slurry and spray dried. The protein solubility of the neutralized product is quite high, giving NSI values above 60%, provided that white flakes were used as the starting material.
The liquid extract containing sugars, minerals, the protein fractions which are soluble at pH 4.5, and other soluble components is usually known as “whey”, in analogy to the process of cheese making. Unlike cheese whey, however, soy whey has no use and must be discarded as waste. The reasons for not using soy whey for animal feeding will be discussed in the next chapter, dealing with isolated soybean protein.
5-3-3 Heat denaturation/ water extraction process
In this process, the proteins of defatted soy meal are first rendered insoluble by thermal denaturation, using humid heat. The heat-treated meal is extracted with hot water, which dissolves the sugars.
5.4 Utilization
5-4-1 Basic considerations
Just as with soy flours, soy protein concentrates are used in food products for their nutritional characteristics or for their functional properties or for both.
Nutritionally, the attractive features of concentrates include their high protein content, the near-absence of anti-tryptic and other anti-nutritional factors, the absence of flatulence and the substantial “dietary fibre” content. The nutritional value of the protein in the concentrates of different types, expressed as Protein Efficiency Ratio (PER) is slightly lower than that of soy flour protein. (Table 5-2). This is probably due to the slight fractionation effect of the extraction process, mentioned above.
Table 5.2 Per * value of soy protein products
(*) The PER values corrected to: casein = 2.5 Source: Soy Protein Council (1987)
The most important functional characteristics of soy protein concentrates are: water binding (water adsorption) capacity, fat binding capacity and emulsification properties.
5-4-2 Use in bakery products
Unless higher protein fortification levels are necessary, there is no special reason for using soy protein concentrates in bakery products. Nutritionally and functionally, soy flours do the same job, more economically.
5-4-3 Meat products
This area probably represents the most important application of soy protein concentrates in the food industry. SCP is used mostly in comminuted meat, poultry and fish products ( patties, emulsion type sausages, fish sticks etc.) to increase water ant fat retention. The nutritional contribution of soy protein in low-meat, high-fat, low-cost products may also be significant. Typical usage levels, on moisture-free basis, are: 5-10% in patties, 2-8% in chili, 2-12% in meatballs, 3.5% max. in sausages, 5-10% in fish sticks. (Campbell et al. 1985).
5-4-4 Other uses
Soybean protein concentrates have been used as stabilized dispersions in milk-like beverages and simulated dairy products such as sour cream analog. Campbell et al.(1985) present a formula for a milk-like beverage, suggested by A.E. Staley Mfg. Co., producers of the soy protein concentrate and the corn syrup solids components in the formula. The formula and directions for the preparation of the beverage are given below:
Formula for “Soy Concentrate Milk”:
Soy protein concentrate
6.0 %
Sucrose
0.6 %
Corn syrup solids
2.0 %
Fat
3.0 %
Mono-and di-glycerides
0.1 %
Salt
0.05 %
Water
88.25 %
The SCP is hydrated with water in a high-shear mixer, then all other ingredients, except the fat are added and mixed thoroughly. The mixture is heated to 65-70oC. The fat (apparently a hydrogenated, well deodorized oil) and flavouring agents are added. The mixture is homogenized, cooled and packaged.
Non-dairy coffee whiteners can also be made, using the same principle, but different ingredients and proportions.
6. ISOLATED SOYBEAN PROTEIN (ISP)
6.1 Introduction
Isolated soybean proteins, or soybean protein isolates as they are also called, are the most concentrated form of commercially available soybean protein products. They contain over 90% protein, on a moisture free basis.
Soy protein isolates have been known and produced for industrial purposes, mainly as adhesives for the paper coating industry, well before World War II. ISP’s for food use, however, have been developed only in the early fifties.
The basic principles of ISP production are simple. Using defatted soy flour or flakes as the starting material, the protein is first solubilized in water. The solution is separated from the solid residue. Finally, the protein is precipitated from the solution, separated and dried. In the production of ISP for food use, in contrast to ISP for industrial use, care is taken to minimize chemical modification of the proteins during processing. Obviously,the sanitary requirements are also much more demanding.
Being almost pure protein, ISP can be made to be practically free of objectionable odour, flavour, colour, anti-nutritional factors and flatulence. Furthermore, the high protein concentration provides maximum formulation flexibility when ISP’s are incorporated into food products. These and other advantages have been the source of highly optimistic forecasts regarding the widespread use of ISP. Although the volume of production increased and although several production facilities have been erected in the U.S.A., Europe, Japan, India and Brazil, the tonnage figures are far from those predicted when food grade ISP was first marketed.
The principal reasons for this situation are the relatively high production cost (see below), nutritional and regulatory limitations, the inability of ISP-based texturized products to compete with texturized soy flour and texturized SPC, and finally, the competition of other abundant “isolated proteins”, particularly casein and caseinates. Nevertheless, it should be noted that many novel isolated proteins, such as those obtained from cottonseed, peanuts, fish, squid etc. have been much less successful than ISP. Many of these did not reach the stage of commercial production.
Although actual trade figures are not disclosed, the growth in sales of concentrates and isolates is said to be, at present, stronger than that of flours.
ISP can be further modified and processed into more sophisticated products. These include: spun fibres from ISP as an ingredient for muscle food analogs, proteinates and enzyme modified ISP.
The cost of isolated soybean proteins is five to seven times higher than that of defatted soy flour. On an equal protein weight basis the cost ratio of these two products is nearly 3:1. The main reasons for the added cost will become evident from the description of the manufacturing methods for ISP.
6.2 Defintion, composition, types
The specification of the Association of American Feed Control Officials, Inc. (AAFCO) defines ISP is as follows:
“Soy Protein Isolate is the major proteinaceous fraction of soybeans prepared from dehulled soybeans by removing the majority of non-protein components and must contain not less than 90% protein on a moisture-free basis.” (from ’90 Soya Bluebook).
There are no official standard definitions or specifications for the various types of isolates. ISP is bought and sold on the basis of specifications formulated by the manufacturer or the user.
The typical composition of an isolated soy protein is shown in Table 6-1.
Table 6.1 Typical composition of ISP (Moisture-free basis)
Source: Kolar et al. (1985)
The conventional procedure for ISP production is based on protein solubilization at neutral or slightly alkaline pH, and precipitation by acidification to the isoelectric region, near pH 4.5. The resulting product is “isoelectric ISP”. It has low solubility in water and limited functional activity. Different “proteinates” can be produced by resuspending isoelectric ISP in water, neutralizing with different bases and spray-drying the resulting solution or suspension. According to the base used for neutralization sodium, potassium, ammonium or calcium “proteinates” are produced. The first three are highly soluble in water, producing solutions with very high viscosities, foaming, emulsification and gel-formingproperties. Calcium proteinate has low solubility. Low-solubility (inert) ISP’s are used where the formulation calls for a high level of protein incorporation without excessive viscosity of other functional contributions.
Since spray-drying is the common drying method in the production of ISP, the primary physical form of ISP in commerce, is that of fine powders. Structured forms, such as granules, spun fibres and other fibrous forms are made by further processing. These forms will be discussed in a separate chapter, dealing with texturized products.
6.3 Production processes
6-3-1 The conventional process
This is the process commonly described in the literature and suggested by suppliers of equipment and complete plants. Exact processing conditions and the type of equipment used may vary from plant to plant.
An outline of the process is given in Fig.30.
a- Starting material:Dehulled, defatted, edible grade white flakes or meal with the highest possible protein solubility index are used. Although the rate of protein extraction from finely ground flour would be faster, flakes permit easier separation after extraction. In batch extraction, particle size has no effect on protein extraction yield, if extraction time is over 30 minutes.
b- Protein extraction: The flakes are mixed with the extraction medium in agitated, heated vessels. The extraction medium is water to which an alkali such as sodium hydroxide, lime, ammonia or tri-basic sodium phosphate has been added, so as to bring the Ph to neutral to slightly alkaline reaction. Under these conditions, the majority of the proteins go into solution. The sugars and other soluble substances are also dissolved.
* Alkalinity: More protein can be extracted at higher pH. However, the extracted proteins may undergo undesirable chemical modifications in strongly alkaline solutions. These include protein denaturation and chemical changes in amino acids. Excessively high pH also favours protein-carbohydrate interaction (Maillard reaction) which results in the formation of dark pigments and in loss of nutritive value. Furthermore, proteins precipitated from highly alkaline media tend to retain too much water, and do not settle well. In practice, the range between pH 7.5 and pH 9.0 is most commonly preferred.
One of the chemical reactions of amino acids in alkaline media has attracted particular attention. That is the destruction of the amino acid cystine, with the formation of dehydroalanine. In addition to the nutritional implications resulting from the loss of cystine, there might be also a toxicological aspect to consider. Dehydroalanine can react with free epsilon-amino groups of lysine, to produce lysinoalanine. This compound has been found to cause kidney lesions in rats under certain experimental conditions. The toxicity of lysinoalanine for man is still an open question.
* Extraction time: The course of nitrogen extraction from white flakes , using 0.03 molar calcium hydroxide as extractant is shown in Fig. 31. The amount of nitrogen extracted under these conditions increased steadily during the first 30 minutes and reached a nearly constant level after 45 minutes. The extraction time in industrial operation is, probably, in the order of 1 hour.
* Temperature: Protein extraction yield is considerably increased by raising the temperature, up to 80°C.
* Solid/liquid ratio: Protein extraction yield is improved as the quantity of liquid medium used to extract a given weight of flakes is increased. After extraction and separation by filtration or centrifugation, the extracted flakes retain a considerable proportion of extract, about 2.5 times the weight of solid. In single-stage batch extraction, if the more liquid is used for extraction, the protein concentration in the extract is lower and the quantity of protein associated with the retained portion of the extract is smaller. On the other hand, larger volumes of liquid have to be handled per unit weight of protein produced. This means larger extraction vessels, centrifuges etc. and a larger volume of “whey” for disposal.
The choice of a solid/liquid ratio for extraction is, therefore, a matter of economical optimization. The ratios used in industry range apparently between 1:10 and 1:20.
* Heat treatment history of the meal: The NSI value of the starting material is the most important factor affecting isolation yield. (Fig. 32)
* Agitation: As in any extraction operation, agitation increases the rate of protein solubilization. However, within the practical values of extraction time for batch operations (about one hour), little is gained by increasing the turbulence beyond that provided by moderate agitation. Furthermore, strong agitation causes excessive flake disintegration, increases the proportion of fine particles in the extract , rendering solid/liquid separation more difficult. Moderate agitation can be defined as any mixing operation that would keep the flakes in suspension within the extraction medium.
c- Solid-liquid separation after extraction:The extract contains considerable amount of fine particles of extracted flour, the elimination of which, prior to precipitation, is necessary in order to obtain a “curd” of acceptable purity. Table 6-2 shows the effect of fine solids separation on the purity of the final product.
In industrial scale operation, it may prove convenient to carry out the extract clarification process in two steps: screening (vibrating screen, rotary screen or the like) to separate most of the solids, followed by centrifugal clarification of the extract. The wet solids can be pressed to remove as much entrapped extract as possible. All these operations can also be carried out in one step, using decanter centrifuges. A flow diagram of decanter-based process for the production of ISP is shown in Fig. 33.
d- Extract treatment:The clarified extract can be treated so as to remove certain impurities, thus improving the blandness, colour and nutritional quality and modifying the functional properties of the final product. Extract treatment may include: ion exchange to remove phytate and reduce the ash content, treatment with activated carbon to remove phenolic substances, ultrafiltration for concentration and removal of low molecular weight components etc. Although such processes have been suggested in the literature it is not known whether they are practised in the industrial production of ISP. The use of membrane processes for extract purification and concentration have been reported to be industrially applied in Europe and Japan. (Elias, 1979).
e- Precipitation: The protein is precipitated from the extract by bringing the pH down to the isoelectric region. The type of acid used or the temperature of precipitation do not affect the yield or purity of precipitated protein.
f- Separation and washing of the curd:The precipitated protein (curd) is separated from the supernatant (whey) by filtration or centrifugation. Desludger or decanter centrifuges can be used for this purpose. The curd must be washed in order to remove residues of whey solubles. This can be done by resuspending the curd in water and re-centrifuging, or continuously on a rotary or belt filter. Thorough washing is most important for the obtention of high purity ISP.
g- Drying: The usual method for drying the washed curd is spray-drying.
6-3-2 Problems in conventional processing
a: Process losses: The conventional process separates the soy solids into three fractions: extraction residue, curd (ISP) and whey.
Extraction residue (okara) is the insoluble solid material left behind after extraction and separated from the extract by filtration or decanting. It represents approximately 40% of the solids in the raw material and carries away 15% of the protein entering the process. It is usually pressed, dried and sold as a by-product of ISP manufacture. It can be used as a protein source for animal feeding rations or as a source of dietary fibre in human nutrition. It has been also used in food products for its exceptional water adsorbing capacity.
Whey is the liquid supernatant, after the protein is precipitated from the extract. It contains the sugars and the nitrogenous substances not precipitated by acidification.
Approximately 25% of the dry matter of the raw material and 10% of its nitrogen content is found in this fraction. Early investigations ( Hackler et al. 1963) indicated that soybean “whey” may be toxic to animals. This finding has been reconfirmed often since then. Furthermore, ISP whey is a highly diluted stream, containing 1 to 3% solids depending on the solvent:flake ratio used for extraction. Concentration and drying of ISP whey would be too costly. ISP whey is , therefore, a waste stream of the isolation process.
The curd is the precipitate obtained by acidification of the extract. After washing and drying, it becomes the final product: isoelectric ISP. It contains 75% of the protein of the starting material. Nearly 3 tons of defatted soybean are needed to produce one ton of protein isolate.
This low yield explains, to a large extent, the relatively high cost of ISP.
b: Quality: ISP obtained by the conventional process contains several types of impurities ( e.g. phytates and phenolic substances) which may somewhat impair its functional,sensory and nutritional quality. More complete dehulling of the beans , thorough extract clarification and repeated washing of the curd reduce the impurities but does not eliminate them completely.
6-3-3 Alternative processes
Several alternative processes for the isolation of soy protein have been reported in the literature. These include:
a: Solubilization of the soy proteins in the salt solutions (salting-in) followed by precipitation by dilution with water.
b: Precipitation from the extract at near-boiling temperature, using calcium salts ( as in the production of Tofu).
c: Ultrafiltration of the extract so as to remove the low molecular weight components of the whey , leaving a concentrated solution of protein which may be spray-dried.
d: Physical separation of the intact protein bodies from very finely ground soy flour by density fractionation (flotation).
e: Purification of the extract by ultrafiltration, filtration through activated carbon and ion exchange, in order to increase curd purity.
6.4 Utilization
6-4-1 Meat products
In this paragraph, only the use of non-texturized ISP and proteinates will be discussed. It should be remembered, however, that the major application of ISP in connection with meat and related product is based on the use of texturized ISP, in one form or another, to replace meat. This application will be dealt with later on.
In emulsion type sausages, such as frankfurters and bologna, ISP and proteinates are used for their moisture and fat binding properties and as emulsion stabilizers. Typical usage levels are 1% to 4% on a prehydrated basis. The use of ISP in these products permits reducing the proportion of expensive meat in the formulation, without reducing the protein content or sacrificing eating quality.
Methods for incorporating soy protein products into whole muscle meat have been developed recently. Isolated soybean protein is dispersed in specially formulated meat curing brines and injected into whole muscle using stitch pumps. It is also possible to incorporate the protein by surface application of the protein containing brine, followed by massaging or tumbling, as practised in the cured meat industry. Typical brine formulations contain salt, sugars, phosphates, nitrite and/or ascorbic acid.
6-4-2 Seafood products
The most important of application in this category is the use of ISP in fish sausage and surimi based restructured fish products in Japan. Surimi is extensively washed, minced fish flesh.
6-4-3 Cereal products
ISP is sometimes used instead of, or in combination with isolates and soy flour, in the formulation of milk replacer mixtures in bakery products. ISP has been used for protein fortification of pasta and specialty bread. In these applications, the high protein content and blandness of ISP are clear advantages.
6-4-4 Dairy-type products
Soybean protein isolates are used in non-dairy coffee whiteners, liquid whipped toppings, emulsified sour cream or cheese dressings, non dairy frozen deserts etc. The basis for these applications is, demand for non-non-dairy (all-vegetarian, cholesterol-free, allergen-free) food products, as well as economy.
Imitation cheeses have been produced from isolated soy proteins, with or without milk whey components. The types of cheeses which can be produced include soft, semi-soft, surface-cultured (imitation Camembert) and ripened hard cheeses.
6-4-5 Infant formulas
Infant formulas where milk solids have been replaced by soy products are well established commercial products. ISP is the preferred soy ingredient, because of its blandness, absence of flatus-producing sugars and negligible fibre content.The principal market for these products are lactose-intolerant babies. However, soy protein based dietetic formulas are finding increasing use in geriatric and post-operative feeding as well as in weight reduction programs.
6-4-6 Other uses
Partially hydrolysed soy proteins possess good foam stabilization properties and can be used as whipping agents in combination with egg albumen or whole eggs in confectionery products and deserts.
Isolated soybean protein has been shown to be an effective spray-drying aid in fruit purees. In this application, it can replace maltodextrins, with the advantage of contributing protein to the final product. A nutritious “shake” base was produced by spray-drying ripe banana puree containing up to 20% ISP on dry matter basis. (Mizrahi et al.,1967).
7. TEXTURED SOY PROTEIN PRODUCTS
7.1 Introduction
For many years, the newly developed soy protein products did not make much progress in occupying a central position in the global protein nutrition picture. The first processed soy protein products were mainly flours or powders which had to be “concealed” in existing foods such as bread, pasta or beverages. The objective of a great part of the research effort was to render these powders sufficiently flavourless and white, and to counteract any change in the accepted characteristics of the “host” food caused by the incorporation of soy protein products at nutritionally and economically significant levels. A breakthrough in the utilization volume occurred in the 1960s, when textured soy protein products of acceptable quality became increasingly available.
Applied to soy protein products, the terms “texturization or texturing” mean the development of a physical structure which will provide, when eaten, a sensation of eating meat. Meat “texture” is a complex concept comprising visual aspect (visible fibres), chewiness, elasticity, tenderness and juiciness. The principal physical elements of meat which create the texture complex are: the muscle fibres and the connective tissue.
A voluminous patent and research literature on vegetable protein texturization has accumulated.( See e.g.Gutcho, 1977). In fact, a meat analog based on wheat gluten was being used for institutional feeding already before the start of our century. A concept of a soy protein based chewy gel and processes for its production have been described in several patents in the late 1950s. ( e.g. Anson and Pader 1957). These inventions produced homogeneous, isotropic (unoriented, of equal structure in all directions) gels, which had only one of the elements of meat texture: chewiness. They had limited commercial success.
The more successful approaches to soy product texturization can be classified in two categories. The first approach tries to assemble a heterogeneous structure comprising a certain amount of protein fibres within a matrix of binding material. The fibres are produced by a “spinning” process, similar to that used for the production of synthetic fibres for the textile industry. The second approach converts the soy material into a hydratable, laminar, chewy mass without true fibres. Two different processes can be used to produce such a mass: thermoplastic extrusion and steam texturization.
It should be noted that the term “meat” is used here in the wide sense of “flesh food”, and includes not only red meat but also poultry, fish and seafood.
The starting material for spun fibres is isolated soybean protein. In contrast, extrusion or steam texturized soy products can be made from flour, concentrate or isolated protein.
7.2 Spun-fibre based texturization
The process for the production of textured soy products containing spun protein fibres was first described in a 1954 patent issued to Boyer. Since then many additions to and modifications of the basic concept have been suggested. The basic flow-diagram of the process is shown in Fig. 34.
The first part of the flow diagram describes the steps for the production of isoelectric isolated soybean protein. These steps can be omitted if commercial ISP is used as the starting material. A concentrated protein solution is prepared by adding alkali to the ISP slurry. The solution , containing approximately 20% protein at pH 12 to pH 13 is “aged” ( to permit unfolding of the protein molecules) until its viscosity rises to the consistency of honey (50,000 to 100,000 centipoise).This viscous concentrated protein solution is technically known as “dope“.
The next step is the transformation of the dope into distinct, stretched fibres (spinning) by coagulating fine jets of the solution in an acid bath.The “dope” is pumped into the coagulating bath through a spinneret, which is a plate with thousands of fine holes (about 75 microns in diameter). The bath contains a solution of phosphoric acid and salt, maintained at pH of about 2.5. As the jet of “dope” contacts the acid medium, the oriented protein molecules are suddenly coagulated and form a fibre. The fibres are picked up as a “tow” and stretched to enhance molecular orientation and increase fibre strength. Stretching reduces the diameter of the fibre well below that of the holes on the spinneret.
The tows of fibre pass through a step of washing, to remove excess acidity and salt. The subsequent operations depend on the final product. Soy protein fibres are only one ingredient of the meat-like structure. The other ingredients include fat, binders, colouring and flavouring additives etc. The nature of these ingredients, the proportion of fibres and their orientation in the binder matrix depend on the type of flesh food to be imitated. The binder matrix contains heat-coagulable components, commonly egg albumen and the final structure is usually stabilized by thermal setting.
Spun fibre-based textured soy products have been used as “total” meat analogues (i.e. to replace meat totally) and as meat extenders (i.e. to replace part of the meat in ground meat, patties etc.) Some of the products have been used in institutional feeding (hospitals) and in school lunch programs.
The main shortcoming of spun fibre type texturized products is their cost. In the first place, the process requires an expensive starting material: isolated soybean protein. Furthermore,t he process in itself is also costly, both in initial capital investment and in running expenses.
Today, there are very few producers of spun soy protein fibres and textured products containing them. The most successful spun fibre based meat analog has been the imitation bacon chip. This is a shelf-stable low-moisture product with the bite, chewiness and flavour of fried or roasted bacon bits and is used extensively in salads, snacks and garnishes. At present, however, this product too faces the competition of imitation bacon made by the less expensive extrusion texturization technique.
7.3 Extrusion texturization
Extrusion has been long used as a central unit operation in the plastic polymer industry. Their use for continuous pressure-cooking of flours and particulate feed materials has been advocated in the 1950s. A decade later, Mc.Anelly (1964) described a process for the production of spongy, elastic particles from soy flour. A mixture of defatted flour and water was extruded through a food grinder. The extruded strands were heat-set in an autoclave, chopped, leached with hot water and dried. Although this invention can be considered as the forerunner of the extrusion texturization processes, the breakthrough in this field was the disclosure of a continuous cooking-extrusion process, for which a patent was awarded to Atkinson in 1970. In this process, defatted soy flour containing a certain amount of water is passed through a high-pressure extruder-cooker to produce an expanded, porous, somewhat oriented structure described as “pleximellar”. Although devoid of true fibres, the product possessed the textural characteristics of chewiness and elasticity, and was deemed to imitate meat in this respect. Extrusion texturized soy flour soon became an established food ingredient known as TVP ( Textured Vegetable Protein ) or TSP (Textured Soy Protein).
The extruder consists basically of a sturdy screw or worm rotating inside a cylindrical barrel (Fig. 35). The barrel can be smooth or grooved. The screw configuration is such that the free volume delimited by one screw flight and the inside surface of the barrel decreases gradually as one goes from one end of the screw shaft to the other.
As a result of this configuration, the material is compressed as it is conveyed forward by the rotating screw. Screws having different compression ratios are used for different applications. The barrel is usually equipped with a number of sections of steam heated jackets or induction heating elements or cooling jackets. A narrow orifice or “die” is fitted at the exit end of the barrel. The shape of the die opening determines the shape of the extruded product.
Defatted soy flour with a high protein solubility index is first conditioned with live steam, before entering the extruder proper. Well controlled conditioning is essential for good texturization and product uniformity. The moisture content of the feed is very important. A moisture level of about 20-25% is used for texturization. The conditioned flour usually assumes the form of small spheres.
The flour-water mixture is next fed into the extruder and picked up by the screw. As it advances along the barrel, it is rapidly heated by the action of friction as well as the energy supplied by the heating elements around the barrel. The high pressures attained through the comression mechanism explained above permits heating to 150-180°C. This rapid “pressure cooking” process transforms the mass into a thermoplastic “melt”, hence the name of “themoplastic extrusion” by which the process isalso known. The directional shear forces causes some alignment of the high molecular weight component while the proteins undergo extensive heat denaturation. The sudden release of pressure causes instant evaporation of some of the water and “puffing”. The result is a porous, laminar structure. Puffing and therefore porosity can be controlled by monitoring melt temperature at the die. If a dense product is desired, the melt is cooled at the final section of the barrel, just before entering the die.
The extrudate is cut continuously by a rotating knife as it emerges from the die. It may be dried and sold as a shelf-stable product, or it can be hydrated, flavoured, mixed with other ingredients, shaped and marketed, usually, as a frozen food.
While texturizing the soy material, extrusion cooking also provides the heat treatment necessary to reduce the microbial load and to inactivate the trypsin inhibitor. It should be noted that, despite the high temperatures in the extruder, trypsin inhibitor inactivation may be incomplete, due to the relatively short processing time.
The so-called low-cost extruders which have been mentioned in connection with the continuous heat treatment of full fat soy flour or corn-soy-milk (CSM) food supplements are not suitable for texturization. These extruders work with low-moisture feeds and provide heat mainly by friction. The extrusion-cooking machines used for texturization are more sophisticated and expensive. Recently, double-screw food extruders have been replacing the older single-screw models in food processing applications. In double-screw extruders a considerable part of the mixing and friction-heating effect takes place between the screws. The shafts can be fitted with interchangeable screw elements, providing different processing profiles along the extruder.
Extrusion texturized soy flour has been called “the first generation TVP”. Being made of flour, it has the composition and flavour of heat treated soy flour. The flavour is intensified by retorting. It contains the sugars of soy flour and presents the problem of flatulence. Usage directions usually prescribe a reconstitution step of soaking in water and pressing to remove the soluble components. More recently, processes have been developed for the texturization of soy protein concentrates. Textured concentrates (second generation TVPs) are now widely available.
Table 7-1 compares the characteristics of texturized soy products, according to the starting materials from which they are made.
Since nothing is removed or added in extrusion texturization, the composition of texturized products, on a dry matter basis, is essentially the same as that of the starting material. Shelf-stable dry products are usually marketed at a moisture level of 8%. Texturized soy products made from concentrate do not need to be leached and can be used directly, after proper hydration.
7.4 Steam texturization
Several processes have been described in the patent literature for texturizing soy protein by thermal coagulation coupled with some form of shear induced orientation to provide a fibrous-like structure. In one of these processes, patented by Stromer and Beck (1973), moistened soy flour is fed continuously into a pressurized reactor where it meets high pressure steam (at about 7-8 atmospheres). The thick mass flows, under the action of pressure, through a cylindrical barrel the discharge end of which is open to the atmosphere. The process was sold to one of the leading manufacturers of soy protein products and commercially applied for some time. According to Snyder and Kwon (1987), it is no longer being used.
7.5 Utilization
7-5-1 Meat extenders
The principal use of texturized soy protein products is as a meat extender in comminuted meat product such as patties, fillings, meat sauces, meatballs etc. In such products, as much as 30% of the meat can be replaced by hydrated texturized soy products without loss of eating quality. The cost of textured soy flour is approximately 0.60 U.S. Dollars per kilogram. About 3.5 kilograms of hydrated base is obtained from each kilogram of textured flour. Thus, the cost of meat replacement is only 17 cents of a dollar for each kilogram of meat saved. Furthermore, textured soy products offer not only economic savings but also certain types of product improvement. Their ability to absorb water and fat results in increased product juiciness and permits the use of meat with higher fat content.
Ground beef extended with TVP has been used extensively in school lunch programs, with good results.
The property of TVP to withstand cooking in a retort (retortability, retort stability) is relevant to its use in canned luncheon meat, meat loaf and similar products.
7-5-2 Meat analogs
Chunks of extrusion texturized soy protein products and spun fibre based preparations are marketed as “imitation meat” or “meat analogs”. The market for these products was, at first, limited to the relatively small sector of vegetarians. Recently there is a marked trend to reduce the consumption of red meat, associated with the demand for low-cholesterol foods. At the same time, the industry has been successful in developing more attractive meat analogs made from rehydrated textured soy proteins, alone or in combination with wheat gluten. These products are marketed as flavoured, fully prepared, frozen ready-to eat entrées. The present marketing strategy for meat analogs is to present them to the public as new, high quality products, and not as inexpensive substitutes for meat. So far, this strategy seems to be successful. The market for these sophisticated (and by no means inexpensive) products is rapidly expanding, particularly in Western Europe.
7-5-3 Other applications
Imitation bacon bits based on texturized soy protein products have been mentioned earlier. The price range for this product is 1.50 to 2 U.S. Dollars per kilogram.
A pasta product containing texturized soy protein granules is being offered on the retail market, in addition to its use in institutional feeding.
This is the Index Page for all work related to MDM and Blended Ham Products.
Meat Emulsions – A Roadmap to Investigations
2 October 2020
In April this year, I decided to put everything I thought I knew about fine meat emulsions aside and to start from scratch. This was a very hard week where nothing worked the way I wanted it to work. For a large part, I was flying on autopilot, disregarding my personal extreme disappointment with the world NOT working the way I thought it must work. For several days I was in the test kitchen from first thing in the morning and was the last person to leave. What emerged at the end of the week was not an answer, but a roadmap to the answer.
I went for a run when I got home and the enormity of the breakthrough dawned on me. Let me recap what I decided in April when I embarked on this journey. I questioned everything!
What is the role of equipment? What are starch-, soya-, rinds- and fat emulsions and why create it or use it in the final meat emulsion? What exactly are TVP and the various isolates? What is a modified starch and what are the differences with native starches? What is a food gel and what characteristics are required under which conditions? What is the role of meat proteins in gelation? What is an emulsifier and what is a filler? How did these enter the meat processing world and what has been the most important advances? What is the legislative framework? What is the role of time, temperature, pH, pressure, particle size on these products in isolation and synergistically, in a complex system? What is the role of enzymes in manipulating these? What are all the possible sources of protein, starches, fillers and emulsifiers? How do we enhance taste? Firmness? etc.
The subject is clearly stated by Gravelle, et al. “Finely comminuted meat products such as frankfurter-type sausages and bologna can be described as a discrete fat phase embedded in a thermally-set protein gel network. The chopping, or comminution process is performed under saline conditions to facilitate extraction of the salt-soluble (predominantly myofibrillar) proteins. Some of these proteins associate at the surface of the fat globules, forming an interfacial protein film (IPF), thus embedding the fat droplets within the gel matrix, as well as acting to physically restrain or stabilize the droplets during the thermal gelation process. As a result, these types of products are commonly referred to as meat emulsions or meat batters.” (Gravelle, 2017) I love this concise description and in it is embedded a world of discovery and adventure.
A road-map emerged. It is different from NPD in that in this stage of the game, I assume that I know nothing. I seek to learn as much as possible through experimentation and carefully selected collaborations, done in such a way that confidentiality is not an issue. I assume that I don’t know enough and that the information I have been given over the years may not have been the most correct or complete information. I assume that if I understand the various chemicals and equipment pieces better than most people, I should be able to arrive at answers that others are not able to.
My first task was to set out the framework for investigations. The new investigative techniques that became clear to me this week will only be effective within the right philosophical framework.
Test, test and, when you had enough, test some more!
Develop a way to do rapid testing of various combinations or products in isolation. Test per certain pH, temperature, particle size, etc. Test and test and test some more. Remember to keep careful notes with photos.
Find Solace in the wisdom of the old people.
Often, the greatest food innovations emerge out of an understanding how things were done hundreds of years ago. This is the basis premise of The Earthworm Express.
List Protein Sources
Make a list of all protein sources, their protein content, fat, fiber and other characteristics. What is the state of the proteins? Denatured? Damaged? Get samples and test.
Develop Rapid Test’s
Develop rapid test techniques which are quick, inexpensive and accurately mimics processing conditions. Fed up and frustrated with the restrictive and expensive nature of the test kitchen set-up, it was the realization how to do this that was my biggest breakthrough this week.
Don’t Trust Ingredient Comp’s.
Seek advice, but remember that staff from spice companies will tell you whatever they have to tell you to sell their particular product which may or may not be what you are looking for.
Understand your Equipment
Take the time to understand the different pieces of equipment who purports to fulfill a certain function and compare the results by talking to different production managers who use these equipment pieces. Is smaller better? Heat generated? Damage to proteins?
List binders/ emulsifiers
List all possible binders/ emulsifiers / fillers and test. Get samples and test.
Record and photograph everything!
Record everything. Inclusion (dosage), pH, temperature, reaction time, processing steps. Keep meticulous photo records.
Build an international network of trusted friends
Seek out the advice of people you trust when you run into a dead end. I find it best to have such a network of collaborators across the world. Pick the right peoples brains!
There is ONE least cost formulation for every situation.
I have come to the conclusion that it is merely a matter of data manipulation to arrive at the one ultimate “least cost” solution for every product, in any particular set of circumstances.
Separate the steps and logically group chemical reactions.
Group chemical reactions together and separate steps to achieve optimal results, thus creating different emulsions to be blended together in the final step.
-> Emulsifiers in Sausages – Introduction. Understanding the role and chemistry of non-meat emulsifiers, extenders and fillers is currently widely used in South Africa.
-> Soy or Pea Protein and what in the world is TVP? Here we start to learn about the functional properties brought to the fine emulsion by soy, pea protein and TVP by first understanding exactly what they are and how they are produced.
Over the next years, I want to make this approach part of my daily routine. I am interested to work with collaborators on various aspects of the project.
to the ferric ion of metMb occurs.” Adding ascorbate or erythorbate plays a key role in this conversion. (Pegg and Shahidi, 2000) The issue is not the nitrate itself, but the uncontrolled curing that results from nitrate and the higher residual nitrites.
to give dehydroascorbic acid and NO. Because ascorbic acid competes with amines for 
Alternatively, just enjoy the story! Oh, it is a magnificent story! So magnificent that it reminded me of Minette, my wife! It’s all in the story of the development of tank curing and instead of bacon photos I have photos of my wife because these are both passions of my life!
