Bacon Curing – a historical review.
By Eben van Tonder
31 May 2016
The Curing Process
Salt Only (Dry cure – no pumping)
Salt with a little bit of saltpeter
Salt, Saltpeter and Sugar
Dry-salt-curing in combination with injection (dry cure – with pumping)
Morgan’s Arterial Injection
Was this Morgan’s Invention?
The Australian Connection
What About Other Forms of Injection?
Combining Injection and Wet Curing
Brine Soaking (brine cure – no pumping)
Boiling of the Brine
Wet-curing in combination with injection (brine cure – with pumping)
Multi-Needle Injection and Vacuum Tumbling
This historical review spans many millennia. From the bronze age to our current time where we touch on modern developments in meat curing technology. It deals with some of the developments in brine technology as well as the technology of administering the brine to the meat and accomplish curing in the shortest possible time. This review is done from the perspective of a commercial mainstream high throughput bacon plant and not from the viewpoint of artisan curing operations, some of which are large and service a large client base. It is a work in progress as my own understanding evolves of this great art, the art of curing.
The Curing Process
Curing is a fascinating process. A modern understanding of the benefits of curing is that it fixes a pinkish-reddish cured meat colour. It endows the meat with unique longevity, even if left outside a refrigerator, many times longer than that of fresh meat. It is powerful enough to prevent the deadly toxin formation by Clostridium botulinum. It prevents rancidity of fat. It lastly gives meat a unique cured taste.
Discovering the mechanics behind meat curing was a slow process that took hundreds of years. (for some of the people behind the most important discoveries, see Fathers of Meat Curing) The object was the preservation of meat for future consumption. Bacon and other cured products, properly prepared, have, however, always been a delicacy as it remains to this day. Today, taste and a visual appeal probably dominates, but ask any outdoor’s person and they will tell you that preservation for future consumption is still a huge factor in the immense popularity of cured meats.
A survey of farm curing methods conducted in 1951 by the US Department of Agriculture among farmers in the US revealed the following brining methods used: Dry cure – no pumping, brine cure – no pumping, brine cure – pumped and dry cure – pumped. (Dunker and Hankins; 1951: 4)
For a discussion on the mechanics of curing, refer to my article Reaction Sequence: From nitrite (NO2-) to nitric oxide (NO) and the cooked cured colour.
Salt Only (Dry cure – no pumping)
Exactly where salt curing of meat started is an interesting question deserving far more attention than one would automatically assign to it. Its one of those things that seem “natural.” As if it has been with us forever. The fact is that the technology is neither “natural” nor was it universally practices. For example, no records exist in sub-Sahara Africa of preserving meat with salt. Salt was used as a condiment after the meat was cooked, but preserving meat was always done by drying it only and salt and spices were only added for preservation after Europeans introduced the practice to the sub-continent.
Despite that fact that there are records of fish being salt cured in China going back to 2000 BCE and from Egypt and Mesopotamia, the practice is much older. The earliest sample of cured meat dates back to 5300 years ago (3300 BCE) and remarkably, we don’t have any written record of this since it pre-dates the invention of writing, but a very small sample of the actual cured meat survived in the most unusual manner.
In September 1991, two German hikers from Nuremberg, Helmut and Erika Simon, stumble across the naturally mummified remains of a Copper Age man while wandering through an Alpine glacier at the border between Austria and Italy, on the Austrian-Italian region, in the Ötztal Alps. What they thought was a hiker who perished recently turned out to be the oldest mummified frozen mummy known today. He is estimated to have lived in 3,300 BCE and more specifically between 3359 and 3105 BCE. There is a 66 percent chance that he died between 3239 and 3105 BCE.
The interesting aspect related to our present consideration of meat curing is his last meal. “Researchers thawed his body and have been able to test the contents of his stomach. Mummy specialist Albert Zink from the European Academy of Bolzano said he was able to analyse the nanostructure of meat fibres from a mountain goat found in Ötzi’s stomach – indicating that the meat was raw and had been dry-cured, and not cooked or grilled, which would have weakened the fibres. He added that Ötzi did not have a proper hunting bow with him, and probably carried the dried meat with him from his home, as raw meat would have quickly gone bad. Further analysis of his stomach contents showed that he had not eaten cheese or dairy products, just meat. “It seems probable that his last meal was very fatty, dried meat – perhaps a type of Stone Age Speck or bacon,” Zink said. As Ötzi had hiked down from the South Tyrolean side of the Alps, it’s likely his provisions came from there.” (The Local)
A second interesting fact gleaned from the analysis of his stomick content is where he possibly came from. “When they tested the contents of his stomach, they found a bacterium called Helicobacter pylori, an age-old pathogen that has evolved into different strains according to the region of the world in which it is found. About half the people on the planet harbour the bacterium in their stomachs. It can cause ulcers or gastrointestinal distress and is typically spread among children when they play in the dirt. While researchers cannot be sure if the Iceman was sick due to the infection, they were intrigued by their analysis of the geographic history of the bacterium. “Surprisingly, a strain of bacterium in his gut shares ancestry with an Asian strain,” said the study in the US journal Science. “In contrast to the fact that most modern Europeans harbour a strain ancestral to North African strains.”” (The Local/AFP)
Victor Mair makes the point clear that “DNA-testing revealed that the Icemen (Ötzi) belonged the European haplogroup K, and isotopic tracing of his teeth and bone also point to the fact that he was a native of the Vinschgau or Schnals valley.” (Mair 2004: 112) Since then he was European with Asian connections, the technology to cure meat with salt or/ and nitrogen-containing salts probably came from Western Europe. From the region today occupied by Austria, to be specific. This opens up the tantalizing possibility that migrants such as Ötzi crossed into Asia earlier than 3000 BCE and probably introduced the art of meat curing into Asia. Marco Polo may have looked at an art which his own predecessors took to China, thousands of years before his voyage and which he now had the privilege of re-introducing into a part of Europe. A full circle of sorts.
Salt curing of meat occurred in China from very early on. Flad, et al. (2005) showed that salt production was taking place in China on an industrial scale as early as the first millennium BCE at Zhongba.” Zhongba is located in the Zhong Xian County, Chongqing Municipality, approximately 200 km down-river along the Yangzi from Chongqing City in central China. They state that “the homogeneity of the ceramic assemblage” found at this site “suggests that salt production may already have been significant in this area throughout the second millennium B.C..” Significantly, “the Zhongba data represent the oldest confirmed example of pottery-based salt production yet found in China.” (Flad, et al.; 2005)
“When Marco Polo arrived in China in the 13th century, he was there to pilfer. Impressed with the culture and customs he saw on his travels, he returned to Venice with Chinese porcelain, paper money, spices, and silks to introduce to his home country. It was from his time in Jinhua, a city in eastern Zheijiang province, he found ham.
Salt-cured Chinese hams have been in production since the Tang Dynasty (618-907AD). First records appeared in the book Supplement to Chinese Materia Medica by Tang Dynasty doctor Chen Zangqi, who claimed ham from Jinhua was the best. Pork legs were commonly salted by soldiers in Jinhua to take on long journeys during wartime, and it was imperial scholar Zong Ze who introduced it to Song Dynasty Emperor Gaozong. Gaozong was so enamoured with the ham’s intense flavour and red colour he named it huo tui, or ‘fire leg’. (SBS) An earlier record of ham than Jinhua-ham is Anfu ham from the Qin dynasty (221 to 206 BCE). In the case of Ötzi, however, I am not sure on what basis the conclusion will be reached that it was dry-curing with salt only. Certainly, there could have been some curing salt added.
I recently visited New Zealand where I learned that the Māori never developed salt extraction in any form. I did a short review of the colonization of Indonesia and salt extraction technology in an article, “Concerning the lack of salt industry in pre-European New Zealand and other tales from Polynesia and the region”
A brief survey of the history of salt extraction from China, Fiji, Samoa, New Guinea, Vanuatu and Taiwan yielded fascinating insights. The preeminence of China in shaping salt extraction technology cannot be doubted. One of the earliest forms of salt extraction was to boil seawater. This was widely practiced in Taiwan from where the technology spread across the region. The references of it in Polynesia and Asia offers a suggested progression of the extraction of salt from seawater.
I recently did an article where I looked at fermentation as one of the oldest forms of meat preservation and we discovered that meat was preserved in water before fire and cooking became part of food preparation. As fire became widely used for meal preparation, it would have been natural to boil the meat in the exact liquid (sea/ salt water) it has been stored in very successfully for millennia. (How did Ancient Humans Preserve Food?)
It would have added to the foods taste and probably the primary reason being preservation. Data from Fiji shows that population size, even located by the sea, is a key function of the development of salt extraction technology. Inland communities had the added problem by its removal from seawater.
It would be my guess that migrants from Taiwan would have spread their technology throughout the lands of Polynesia. The boiling off of water to leave only the salt crystals would be associated with an increased population even by the sea and the formation of inland communities. Every evaluation of salt on the islands which we considered supports this. China would undoubtedly have been a key driver in the region in progressing salt extraction technology with Pappa New Guinea playing a large role with its own unique approach. Solar evaporation of seawater, extracting salt through plant material and burning plants, naturally high in salt are a few of the developments from the region, which all presumably have their roots in the practice of simply boiling seawater; in turn, this was probably a progression of the practice of cooking food in seawater; which, in turn had its roots in storing meat in saline solutions; which had its roots in simply immersing carcasses in bodies of water for storage. When we are at this point, we are clearly at the very early age of the existence of anatomically modern humans.
In a discussion with a curator from the Canterbury Museum about the matter of salt production and trade in salt being absent from New Zealand ancient history, he drew my attention to the interesting practice of the Maori to slow boil large quantities of shellfish. Had they not done so, it would not have been possible to consume large quantities at a time. There seems to be evidence that they did, in fact, consume large quantities of this at a time. It supports the notion that they knew about salt and the possibility exists that this was true across the world from very early. People probably knew at least some of the techniques of extracting it, but some local populations, as was the case in New Zealand, may never have used the technology simply because it was not necessary. In the case of the Maories, they definitely knew to remove some of the salt from shellfish before consuming it. (They have a word for salt which shows that they definitely knew about its taste).
This study of salt also brings me back to my work on nitrite/ nitrate curing which has been a major focus for me over many years. While people living in desert areas would have discovered that certain salts have the ability to change the colour of meat from brown, back to pinkish/ reddish, along with increased preservation power and a slightly distinct taste, it is certainly true that coastal dwellers would have observed the same. They would have noticed that sea salt or bay salt have the same ability.
Dr. Francois Mellett, a renown South African food scientist, sent me the following very interesting theory about the earliest discovery of the curing process in a private communication between us on the matter. He wrote, “I have a theory that curing started even earlier by early seafarers: when a protein is placed in seawater, the surface amino acids are de-aminated to form nitrite for a period of 4 to 6 weeks. Nitrite is then converted to nitrate over the next 4 weeks. Finally, ammonia and ammoniac are formed from nitrate. It is possible that they preserved meat in seawater barrels and that the whole process of curing was discovered accidentally.”
I think he is on the right track. I suspect that people discovered this even long before barrels were invented. The use of seawater for meat storage and further preparation was so widespread that it would have been impossible not to have noticed meat curing taking place. If it is generally true that earliest humans first settled around coastal locations before migrating inland, it could push the discovery of curing many thousands of years earlier than we ever imagined, to a time when modern humans started spreading around the globe. When did it develop into an art or a trade is another question altogether, but I think we can safely push the time when it was noticed back to the earliest cognitive and cultured humans whom we would have recognized as thinking “like us” if we could travel back in time and meet them. I think the question of recognition in different regions we can safely put at the time when these areas were populated.
We know that dry curing of pork takes around 5 to 6 weeks under the right conditions and if the meat is not cut too thick. It must be cool enough that the meat don’t spoil before it is cured. Even though I now suspect that curing was first noticed by communities living by the sea as I just explained, I suspect that curing salts in deserts were discovered since natural salts always appear as a mix of various salts and under certain conditions, these salt deposits contain small amounts of nitrate salts and ammonium chloride.
The ancients would have noticed this. I deal with these salts below under separate headings, but the most important two curing salts that appear to us from antiquity are saltpeter (sodium nitrate) and sal ammoniac (ammonium chloride). Both salts were well known in Mesopotamia and references to them appear alongside references to salt curing of fish mentioned earlier and both salts were used in meat curing.
The ancients developed basic techniques of separating out the different salts. In particular, sal ammoniac was by far the more important salt of the bronze age (2000 BCE). It was produced in Egypt and mined in Asia. There are features of sal ammoniac that favours it as a salt for people who had a motivation to exploit new lands due to population pressure and climate changes. When the horse was domesticated around 5000 BCE, a food source was needed to sustain them on long expeditions and I believe sal ammoniac fits the requirement perfectly.
Both salts cure the meat in a week which obviously had huge advantages over salt-only curing. This, I speculate, was the first incentive to change to a dedicated curing salt. Secondly, sal ammoniac, as far as I can find, was globally traded from much earlier on than saltpeter. Ancient Macedonian records indicate that even 2000 BCE saltpeter was preferred in food over sal ammoniac on account of the better taste of saltpeter.
There is a modern era example of a curing technique that was good for a time and was then replaced with more agreeable methods as soon as supply lines were established. This technique, I believe actually existed from very early after the horde was domesticated and was re-introduced by various cultures, at various times. One such culture was the Boers who left the Cape Colony and moved into the interior of South Africa. The technique they used to cure their meat disappeared as soon as conventional supply lines were established.
The technique is curing of meat by hanging it over the neck of the horse or placing it under your saddle so that the sweat of the horse cure the meat. (For a discussion on this, see my article, Saltpeter, Horse Sweat and Biltong) My point is that this is a good example of a curing technique that was used for a time only and then disappeared, only to be re-appear when conditions required it. Such was the case, I suspect when sal ammoniac was used for a time in curing until the requirement subsided, salt curing became popular again and much later economic factors re-introduced saltpeter curing.
German and Austrian cookbooks pre-1600’s reveal that vegetable dyes were used to bolster colour in this time and speak of curing with salt only. It is well known that the Germans and Austrians were familiar with nitrate curing and, I will argue, they would have been acquainted with sal ammoniac as a curing salt also, but for whatever reason, these fell out of common practice. When the requirements disappeared for nitrate and sal ammoniac curing of the ancient world, the nations of Europe and China reverted to salt curing.
The many references to salt curing are therefore not surprising in the context of a mature and stable society. A record exists from Cato the Elder who described in 160 BCE. how a ham should be cured. In his Latin work, De Agricultura (On Farming), this Roman statesman and farmer, gives an ancient recipe for curing pork with salt.
“After buying legs of pork, cut off the `feet. One-half peck ground Roman salt per ham. Spread the salt in the base of a vat or jar, then place a ham with the skin facing downwards. Cover completely with salt. After standing in salt for five days, take all hams out with the salt. Put those that were above below, and so rearrange and replace. After a total of 12 days take out the hams, clean off the salt and hang in the fresh air for two days. On the third day take down, rub all over with oil, hang in smoke for two days…take down, rub all over with a mixture of oil and vinegar and hang in the meat store. Neither moths nor worms will attack it.” (economist.com)
Cato may have imitated a process whereby ham’s are smoked over juniper and beech wood. The process was probably imported by the Roman gourmets from Germania. (economist.com) It is possible that the process of curing itself was brought to Rome by the military stationed in Germany.
Salt curing remains an important technique for high-end hams and certain bacons. Like nitrite curing, it yields a particular cured colour, but one that is more deep purple than pink. For the mechanism behind this, refer to a section in my article on the mechanisms of nitrite curing, BACTERIAL/ ENZYMATIC CREATION OF CURED COLOUR.
In 2017 I did an article where I speculated that nitrate curing originated from either the Turpan area in western China or from the Atacama desert in Chile and Peru. In this article, I suggest that nitrate curing of meat is thousands of years old. (Salt – 7000 years of meat-curing) I was working on the assumption that nitrate salts are the only salts that will yield nitrite and nitric oxide, required for meat curing. Between the Atacama desert and Turpan in Western China, Turpan is by far the best candidate for the birthplace of meat curing as it is practiced around the world. I recently review further evidence from this area in an article, Nitrate Salts Epic Journey and And then the mummies spoke!
In the course of researching the article, I discovered that sal ammoniac was far more vigorously traded than saltpeter in the early Christian era and possibly for thousands of years before that. Fascinatingly enough, I realised that ammonium chloride will, like nitrates, undergo bacterial transformation into nitrites which will, then, in the meat matrix yield nitric oxide which will cure the meat. I further discovered that it is an excellent meat preservative. Turpan is also probably the only place on earth where sal ammoniac and nitrate salts in the form of sodium nitrate occur in massive quantities side by side.
Chinese authors of antiquity are unanimous that sal ammoniac came into China from Turpan, Tibet, and Samarkand and through Samarkand, it was traded into the Mediterranian along the silk road. There are similar records that it was traded from Turpan along the silk road through the city of Samarkand who had strong trading ties with the Mediterranean. It all makes for an appealing case for sal ammoniac as the actual curing salt from antiquity that was used in meat curing when the practice spread around the world. There is even a tantalizing link between Turfan and the ancient city of Salzburg and the salt mines which leads me to speculate that the trade of sal ammoniac was done into the heart of Western Europe, into what became known as Austria. This leads me to believe that the actual technological progressions may have come from Austria. Whether it was Salzburg or Turfan is not clear.
We are not familiar with this salt in the context of meat curing and more information is in order. I reviewed modern references dating back to the 1700’s, 1800’s and 1900’s where it continued to be used in meat preservation in Nitrate Salts Epic Journey. Several minerals exist composed of ammonium (NH4). Ammonium is formed by the protonation of ammonia (NH3). Sal ammoniac is the most well known and was named by the ancient Romans. They collected this salt which was found around the temple of Jupiter Ammon in Egypt and called it salt (sal) of Ammon (ammonocius). The name ammonia was subsequently derived from it. It forms in volcanic vents and after volcanic eruptions before it has rained which dissolves it. It is highly soluble. It is unique in that the crystals are formed directly from the gas fumes and bypass the liquid phase, a process known as sublimation.
Ammonium readily combines with an acid thus forming a salt such as hydrochloric acid to form ammonium chloride (sal-ammoniac) and with nitric acid to form ammonium nitrate. Recent studies have shown that volcanos release a “previously unconsidered flux of nitric acid vapour to the atmosphere. (Mather, T. A., et al, 2004) It is a fact is that the Turfan area, both the basin and the mountains are replete with different salts containing nitrogen (nitrate salts and ammonium) any one of which could be used effectively in meat curing.
The sal ammonia was mined from openings in the sides of volcanic mountains where steam from underground lava flows created the ammonium chloride crystals. These were traded across Asia, Europe and into India. Massive sodium nitrate deposits occur in the Tarim basin, the second lowest point on earth. I then speculate that traders used some of these deposits to forge ammonium chloride since the ammonium chloride crystals did not survive in crystal form on long voyages due to its affinity for water that breaks the crystal structure down. Once this happened, the sodium nitrate and the ammonium chloride look similar in appearance. Due to the fact that it is known that almost all the sal ammonia produced in Samarkand was exported, I deduce that demand outstripped supply and this provided the incentive for such forgery. I find support for the likelihood of such a forgery, not just in the limited supply of sal ammoniac compared to nitrate salts, but also in the fact that mining then sal ammoniac was a seasonal affair and extremely dangerous and a difficult undertaking.
It seems likely that sal ammonia was the forerunner of saltpeter as the curing agent of choice. It is composed of two ions, ammonium, and chloride. The ammonium would be oxidized by ammonia oxidizing bacteria (AOB) into nitrites and the well-known reaction sequence would result. Reaction Sequence
Not only would it result in the reddish-pinkish cured colour, but it was an excellent preservative. An 1833 book on French cooking, The Cook and Housewife’s Manual by Christian Isobel Johnstone states that “crude sal ammonia is an article of which a little goes far in preserving meat, without making it salt.” (Johnstone, C. I.; 1833: 412) It is, of course, the sodium which tastes salty in sodium chloride and ammonium chloride will have an astringent, salty taste. I know exactly what ammonium chloride taste like since it was added to my favourite Dutch candy “Zoute Drop” with licorice. I believe it was none other than my old friend, Jan Bernardo who first gave me Zoute Drop. As a boy, I used to ride my bicycle once a month to the only Greek Caffe in Vanderbijlpark which sold it for my monthly fix. My favourite was the double strength version called “Dubbel Zoute Drop.”
Subsequent to these discoveries, I did two small tests with sal ammoniac. Refer to the Sal Ammoniac Project. Here I show that sal ammoniac stands up to its reputation as an excellent preservative and definitely cures meat in two weeks at a 5 deg C temperature.
Salt with a little bit of saltpeter
Saltpeter is the curing salt that most of us are familiar with that preceded sodium nitrite as curing agent. By far the largest natural known natural deposits of saltpeter to the Western world of the 1600’s were found in India and the East Indian Companies of England and Holland plaid pivotal roles in facilitating its acquisition and transport. The massive nitrate fields of the Atacama desert and those of the Tarim Bason were still largely unknown. In 1300, 1400 and 1500 saltpeter had, however, become the interest of all governments in India and there was a huge development in local saltpeter production.
In Europe, references to natron emerged from the middle of the 1500’s and were used by scholars who traveled to the East where they encountered both the substance and the terminology. Natron was originally the word which referred to saltpeter. Later, the word natron was changed and nitrom was used.
At first, the saltpeter fields of Bihar were the focus of the Dutch East Indian Company (VOC) and the British East Indian Company (EIC). The VOC dominated the saltpeter trade at this point. In the 1750’s, the English East Indian Company (EIC) was militarised. Events soon took place that allowed for the monopolization of the saltpeter trade. In 1757 the British took over Subah of Bengal; a VOC expeditionary force was defeated in 1759 at Bedara; and finally, the British defeated the Mughals at Buxar in 1764 which secured the EIC’s control over Bihar. The British seized Bengal and took possession of 70% of the worlds saltpeter production during the latter part of the 1700’s. (Frey, J. W.; 2009: 508 – 509)
The application of nitrate in meat curing in Europe rose as it became more generally available. Later, massive deposits of sodium nitrite were discovered in the Atacama Desert of Chile and Peru and became known as Chilean Saltpeter. This was, as I have said before, only a re-introduction of technology which existed since 2000 BCE.
The pivotal area where I believe saltpeter technology spread from across Asia, India and into Europe, is the Turpan-Hami Basin in the Taklimakan Desert in China. Here, nitrate deposits are so substantial, that an estimated 2.5 billion tons exist, comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. (Qin, Y., et al; 2012) (THE TARIM MUMMIES OF CHINA) Its strategic location on the silk road, the evidence of advanced medical uses of nitrates from very early on and the ethnic link with Europe of people who lived here, all support this hypothesis.
Large saltpeter industries sprang to the South in Idia and to the South East in western China. In India, a large saltpeter industry developed in the north on the border with Nepal – in the state of Bihar, in particular, around the capital, Patna; in West Bengal and in Uttar Pradesh (Salkind, N. J. (edit), 2006: 519). Here, it was probably the monsoon rains which drench arid ground and as the soil dries during the dry season, capillary action pulls nitrate salts from deep underground to the surface where they are collected and refined. It is speculated that the source of the nitrates may be human and animal urine. Technology to refine saltpeter probably only arrived on Indian soil in the 1300’s. Both the technology to process it and a robust trade in sal ammoniac in China, particularly in western China, predates the development of the Indian industry. It is therefore unlikely that India was the birthplace of curing. Saltpeter technology probably came from China, however, India, through the Dutch East Indian Company and later, the English East Indian Company became the major source of saltpeter in the west.
To the South East, in China, the largest production base of saltpeter was discovered dating back to a thousand years ago. Here, a network of caves was discovered in 2003 in the Laojun Mountains in Sichuan Province. Meat curing, interestingly enough, is also centered around the west and southern part of China. Probably a similar progression to the Indian progression.
In China, in particular, a very strong tradition of meat curing developed after it was possibly first introduced to the Chinese well before 2000 BCE. Its use in meat curing only became popular in Europe gain between 1600 and 1750 and it became universally used in these regions towards the end of 1700. Its usage most certainly coincided with its availability and price. I have not compared price and availability in Europe with the findings on its use in meat curing which is based upon an examination of German and Austrian kook books by Lauder (1991), but I am confident that when I get to it one day, the facts will prove the same.
The Dutch and English arrived in India after 1600 with the first shipment of saltpeter from this region to Europe in 1618. Availability in Europe was, generally speaking, restricted to governments who, in this time, increasingly used it in warfare. (Frey, J. W.; 2009) This correlates well with the proposed time when it became generally available to the European population as the 1700’s from Lauder. I believe that a strong case is emerging that the link between Western Europe and the desert regions of Western China was the place where nitrate curing developed into an art. The exact place, I believe, in Western China is the Tarim depression.
Dry curing of meat changed from salt only to a mixture of salt and saltpeter, liberally rubbed over the meat. As it migrates into the meat, water and blood are extracted and drained off. The meat is usually laid skin down and all exposed meat are plastered with a mixture of salt and saltpeter. Pork bellies would cure in approximately 14 days. (3) (Hui, Y. H., 2012: 540)
Salt, saltpeter and sugar
The addition of sugar which favours the reduction of nitrate to the active agent nitrite became common practice during the 19th century.” (Lauer K. 1991.) At first, it was added to reduce the saltiness of the meat and make it generally more palatable. Curers soon discovered that when sugar is added, the meat cures faster and the colour development is better.
Science later revealed that the sugars contribute to “maintaining acid and reducing conditions favourable” for the formation of nitric oxide.” (Kraybill, H. R.. 2009) “Under certain conditions reducing sugars are more effective than nonreducing sugars, but this difference is not due to the reducing sugar itself. The exact mechanism of the action of the sugars is not known. It may be dependent upon their utilisation by microorganisms or the enzymatic systems of the meat tissues.” (Kraybill, H. R.. 2009)
Ralph Hoagland, Senior Biochemist, Biochemie Division, Bureau of Animal Industry, United States Department of Agriculture, discovered that saltpeter functional value upon the colour of meat is its reduction to nitrites and the nitrites to nitric oxide, with the consequent production of NO-hemoglobin. He showed that the reactant is nitrous acid () or one of its metabolites such as nitric oxide ().
He wrote an important article in 1921, Substitutes for Sucrose in Cured Meats. Writing at this time, this formidable meat scientist is ideally placed to comment on the use of sugar in meat curing in the 1800’s since the basis of its use would have been rooted in history.
He writes about the use of sugar in meat curing in the USA and says that it is used “extensively.” He reveals that according to government records, 15,924,009 pounds of sugar and 1,712,008 pounds of syrup, totaling 17,636,017 was used in curing meats in pickle in establishments that were inspected by the US Government, in 1917. If one would add the estimated use of sugar in dry cures in the same year, he placed the usage at an estimated total of 20,000,000 pounds. This estimate excludes the use of sugar in meat curing on farms. (Hoagland, R. 1921.)
Hoagland says that the functional value of sugar in meat curing at this time (and probably reaching back into the 1800’s) was entirely related to product quality and not preservation. “Sugar-cured” hams and bacon were viewed as being of superior quality. He states that a very large portion of bacon and hams produced in the USA are cured with sugar or syrup added to the cure. The quantity of sugar used in the curing mix is so small that it does not contribute to meat preservation at all. “Meat can be cured in entire safety without the use of sugar, and large quantities are so cured.” (Hoagland, R. 1921.)
The contribution to quality that he speaks about is probably related to both colour and flavour development. The colour development would have been related to the formation of the cured colour of the meat (The Naming of Prague Salt) as well as the browning during frying.
The role of sugar in bacon curing of the 1800’s when saltpeter was used was elucidated in 1882 by Gayon and Dupetit, studying and coining the term “denitrification” by bacteria. The process whereby nitrate in changed to nitrite is through the process of bacterial denitrification. They demonstrated the effect of heat and oxygen on this process and more importantly for our present discussion, “they also showed that individual organic compounds such as sugars, oils, and alcohols could supplant complex organic materials and serve as reductants for nitrate.” (Payne, 1986)
Denitrifying bacteria are facultative anaerobes, that is, they will only use nitrate () if oxygen () is unavailable as the terminal electron acceptor in respiration.” “The is sequentially reduced to more reduced forms although not all bacteria forms gas. ” “Many bacteria can only carry out the reduction of to , and this process is referred to as dissimilatory nitrate reduction. There is also evidence emerging that certain bacteria can denitrify, even if is present. (Seviour, R. J., et al.. 1999: 31)
(Seviour, R. J., et al.. 1999: 31)
“The rate of denitrification is affected by several parameters including temperature, Dissolved Oxygen levels and the concentration and biodegradability of carbon sources available to these cells” (Seviour, R. J., et al.. 1999: 223) Examples of such carbon sources are sugar, oxygen and plant oils.
In the 1800’s when the use of saltpeter was at its pinnacle, the use of sugar with saltpeter had then a much more prominent role in that it energizes denitrification bacteria which results in an increased rate of nitrate reduction to nitrite and therefore would speed up curing with saltpeter and result in a better overall curing process. Today, with the widespread use of sodium nitrite in curing brines, certain denitrifying bacteria is one mechanism for NO formation which directly leads to better curing.
The use of sugar or dextrose in bacon production in the modern era has more to do with the browning effect through by the well-known Millard reaction to give fried bacon a nice dark caramel colour when fried.
Dry-salt-curing in combination with injection (dry cure – with pumping)
It seems that the basic definition distinguishing between dry and wet curing is not based on whether injection is applied or not, but the state of the salts that the meat is left in, even after it has been injected with a brine (mixture of salt and water). So, if it is packed in a dry mix, it is dry curing and if it is soaked in a brine, it is wet-curing.
Morgan’s Arterial Injection
It was a certain Mr Morgan, in England, who invented the technique of injecting a liquid brine into the meat in the first place. The motivation was to increase the rate of curing in order to reduce the time required for processing. In temperatures above 20 deg C, pork spoils in three days.
It was important for farmers to cure the meat before a warm snap could allow spoilage organisms to work before the cure was properly diffused through the meat. Later, in industrial plants, the drive for a faster curing time would be cost factors. Increased output with limited and expensive equipment and people.
By injecting a liquid brine into the meat at evenly spaced intervals, the brine would diffuse quicker through the meat. It is also important to state that his interest was the preserving of meat generally for example for long sea voyages and not the curing of meat by farmers. The application of his method of injection, however, found its way into many homes and factories around the world.
Edward Smith writes in his book, Foods, in 1873 and accounts the events of “Mr Morgan [who] devised an ingenious process by which the preserving material, composed of water, saltpetre, and salt, with or without flavouring matter, was distributed throughout the animal, and the tissue permeated and charged. His method was exemplified by him at a meeting of the Society of Arts, on April 13, 1854, when I [Edward] presided.” (Smith, E, 1873: 35)
He describes how an animal is killed in the usual way, the chest opened and a metal pipe connected to the arterial system. Brine was pumped through gravity feed throughout the animal. Approximately 6 gallons were flushed through the system. Pressure was created to ensure that it was flushed into the small capillaries. Smith reported overall good results from the process with a few exceptions. He himself seemed unconvinced.
An article appeared in the Sydney Morning Herald that mentions Dr Morgan and his arterial injection method. An important observation from the article is the date of 1870. By this date, he is referred to as “Dr Morgan”, cluing us in about the timeline of Morgan’s life.
A second observation is a drawback of the system. The article states that “salting is the most common and best-known process of preservation (of meat), the principal modern novelty being Dr Morgan’s plan of injecting the saline solution into the arterial system – the principal objection to which has been that the meat so treated has been over-salted.” (Sydney Morning Herald, 1 March 1870, p4)
The brine mix that Mr Morgan suggested was 1 gallon of brine, ¼ to ½ lb. of sugar, ½ oz. of monophosphoric acid, a little spice and sauce to each cwt of meat. (Smith, E, 1873: 36)
Seventeen years later after Smith met Mr Morgan at the Society of Arts meeting, in 1871, Yeats reports on a certain “Professor Morgan in Dublin, who has proposed a method of preservation by injecting into the animal as soon as it is killed, a fluid preparation, consisting, to every hundredweight of meat, of one gallon of brine, half a pound of saltpetre, two pounds of sugar, half an ounce of monophosphoric acid, and a small quantity of spice.” (Yeats, J, 1871: 225)
The plan was widely tested at several factories in South America and by the Admiralty, who had reported that they had good results from the technique. (Yeats, J, 1871: 225, 226)
It was in all likelihood the same Morgan that Smith reports on who, by 1871, became a professor in Dublin. One interpretation of the Yeats report is that Morgan, by this time, abandoned his arterial injection method for a more general injection into the muscle. It is also possible that Yeats simply is not concerned with a detailed process description.
Notice, as a matter of interest that he used the same basic brine mix of salt, water, saltpeter, sugar, monophosphoric acid and spices. This, together with the similarity in surname makes it quite certain that Mr Morgan and Prof. Morgan is the same person. In itself, this is an example of perseverance! In 1854 his arterial injection was met with scepticism where Yeats reports in 1871 that the Admiralty viewed his improved method with great interest.
WAS THIS MORGAN’S INVENTION?
The concept of arterial injection was not new. By the time Morgan demonstrated it to the Society of Arts, on April 13, 1854, it may have been as old as 150 years, used for embalming corpses for the purpose of medical studies. This invention is credited by some to the Dutch physician, Frederik Ruysch. (1638 – 1730). He injected a preservative chemical solution, liquor balsamicum, into the blood vessels, but his technique was unknown for a long time. (Bremmer, E.; 2014)
British scientists who used arterial injection and from whom Morgan could have learned the system were the Hunter brothers William (1718–1783) and John (1728–1793) and their nephew, Matthew Baillie (1761–1823). The injection was into the femoral arteries. They all injected different oils, mainly oil of turpentine, to which they added Venice turpentine, oil of chamomile, and oil of lavender. Vermillion was used as a dye to create a more life-like skin colour, but would also have added preservation to the final solution. (Bremmer, E.; 2014)
There is a reference from 1837, on an essay delivered on the operation of poisonous agents upon the living body by Mr John Morgan, F.L.S Surgeon to Guy’s Hospital. (1837; Works on Medicine) The same publication contains an article by Dr Baillie, M.D. on the morbid anatomy of some of the most important parts of the human body. John Morgan was definitely well familiar with arterial injection. Not only due to the fact that he was a contemporary of Baillie, but demonstrator of anatomy at the private school near Guy’s Hospital. (http://livesonline.rcseng.ac.uk/biogs/E000398b.htm)
Despite the fact that I can not locate a single reference, it is not unlikely that he was the father of Dr. John Morgan (Circa 1863), a professor of anatomy at the University of Dublin. A process of arterial injection is described that was used by Dr John Morgan from the University of Dublin. ” John Morgan, a professor of anatomy at the University of Dublin in Ireland, formally established two principles for producing the best embalming results: injection of the solution into the largest artery possible and use of pressure to push the solution through the blood vessels. He also was among the first to make use of a preinjection solution as well as a controlled drainage technique. Morgan’s method required that the body be opened so the heart was visible, then an 8-inch pipe was inserted into the left ventricle or aorta. The pipe was connected to yards of tubing ending in a fluid container hung above the corpse. The force of gravity acting on the liquid above the body would exert about 5 pounds of pressure, adequate to the purpose of permeating the body.” (Wohl, V.) This process described here is applied, not to the preservation of animal carcass, but for embalming a human body! It is, however, the exact same process that he demonstrated years earlier in London to Smith at the Society of the Arts meeting on 13 April related to carcass preservation.
From the process description, it is clear that we have finally identified the Morgan, father of the arterial injection method in meat curing as Dr John Morgan, professor of anatomy at the University of Dublin, son of Dr John Morgan, Surgeon to Guy’s Hospital. The original inventor of the system was the Dutch physician, Frederik Ruysch and the application was embalming.
THE AUSTRALIAN CONNECTION
An 1866 article in the Launceston Examiner reports that Mr Davis, from Adelaide, bought the patent from Dr Morgan. Mr Davis took up “premises at Town Marie, on the Bremer River, about six miles from Ipswich” and the operation of curing commenced.
WHAT ABOUT OTHER FORMS OF INJECTION?
The 1963 Griffith marketing publication they say that they did not invent arterial injection, but developed in further and I assume they are referring to the fact that they did not apply it to carcass preservation, but to injection and curing of hams and shoulders. They also list stitch pumping or bone pumping as it was also called and spray pumping of hams. Spray pumping was also done along the bone in the ham and I assume they are talking about the needle having small spray opening on the side, as is the case with most modern injector needles.
Dr John Morgan from the University of Dublin must rightfully be credited as one of the pioneers of meat injection, as a progression of an original development from the world of mummification, invented by the Dutch physician, Frederik Ruysch. The concept was “in the air,” so to speak and in an 1868 publication, On Food, Letherby says that “saline substances such as saltpeter, acetate of ammonia, sulfite of potash, or soda, muriate of ammonia (sal ammoniac or ammonium chloride) etc, were being injected into fresh meat for the purpose of preservation with several patents pending by Long (1834), Horsley (1847), Murdock (1851) and others. (Letheby, H., 1870)
Combining Injection and Dry-Curing
It is reported today by some bacon curers that they use the dry-curing in conjunction with injection. In this case, the meat is injected with approximately 10% saturated brine solution and the injected meat is then treated the usual way in the application of dry-salt-cure. There is a record showing that the famous Harris from Calne in the United Kingdom used injection with their dry cured bacon from 1843.
After it has been dry-cured, the meat is smoked at a temperature of not higher than 38 deg C (100 deg F) in order to prevent nitrate burn which presents itself as green spots that appear on the meat. Care should also be taken if these products are stored to prevent damage from insects such as cheese skippers, mites, red-legged ham beetles, and larder beetles. (Hui, Y. H., 2012: 540)
Brine-soaking (brine cure – no pumping)
Brine-soaking followed dry-salt-curing. Again, note that dry or wet curing is defined by what the meat if left in to cure and not what is injected into the meat. The process is also relatively slow and meat pieces are placed in a mixture of salt, saltpeter and water. It is important to take temperature into account since spoilage may occur before the brine had a chance to penetrate the meat. (Hui, Y. H., 2012: 540)
An 1830 description of a “wet cure” survived where a farmer describes the dry cure method as “tedious.” He credits Europe as the birthplace of the wet-cure method. One of the benefits of this simple system is that it can be used for mutton and beef also. The down-side is that it is more expensive than dry-cure, but the wet cure could be re-used and taking everything into account, would work out cheaper in the long run than dry-cure. (The Complete Grazier, 1830: 304)
This re-using of the brine would turn out to become the cornerstone of the industrial revolution for bacon curing and the country credited for this development is Denmark. Before we get to that, we have to first look at barrel pork.
Barrel pork was an easy way to cure pork that involved liquid brine. It had the benefit that it could be put in barrels, loaded onto a wagon or a ship for transport and cure in transit. It also had the benefit of being stored in the cure and being safe from flies and other insects.
In the 1800’s, this was the main way that the packing plants in the USA exported pork to England as bacon. There are many accounts in newspapers of the time where advice is given to the bacon producers on how to make sure that the meat arrives in England unspoiled. One of the main points was the importance of using good, new wood for the barrels.
A 1776 description is given on how barrel pork was produced.
“After the meat has cooled < probably after the hair was removed >, it is cut into 5 lb. pieces which are then rubbed well with fine salt. The pieces are then placed between boards a weight brought to bear upon the upper board so as to squeeze out the blood. Afterwards, the pieces are shaken to remove the surplus salt, [and] packed rather tightly in a barrel, which when full is closed. A hole is then drilled into the upper end and brine allowed to fill the barrel at the top, the brine being made of 4 lb. of salt (1.8kg or 10%), 2 lb. of brown sugar (0.9kg or 5%), and 4 gallons of water (15L or 84%) with a touch of salt-petre. When no more brine can enter, the hole is closed. The method of preserving meat not only assures that it keeps longer but also gives it a rather good taste.” (Holland, LZ, 2003: 9, 10)
Again, notice the brine make-up of salt, saltpeter, sugar mixed with water. The role of the sugar was to break the hard salt taste.
Barrel pork would remain an important curing method throughout the 1700’s and would make a spectacular return almost a 100 years later when pressure pumps were introduced to inject the brine into the meat through needles. A plank would be run across the barrel opening. The meat is placed on the plank for injection with between one and three needles. The three needles are fed brine through a hand pump that would pump brine directly from the barrel. The barrel is half filled with brine. After the meat has been injected, it is pushed off the plank, to fall into the brine which acts as a cover brine. It would remain in the cover brine the prescribed time before it is removed and smoked.
Boiling of the brine
We can now return to the 1830 account of wet-curing where we identify important developments in brining technique. The farmer who wrote down the brining technique suggests that the brine mix must be boiled over a gentle fire for the impurities to rise to the top before these were skimmed off and the brine allowed to cool down. (The Complete Grazier, 1830: 304)
When it is cooled down, the brine is poured over the meat so that the meat is completely submerged. Meat from small pigs is kept in the brine for three to four days and longer. An older pig may require one, two, or three days longer. (The Complete Grazier, 1830: 304)
If the meat is intended for hams, it must be left in the brine for two days. At the end of the curing time, rub with pollard (a by-product from the milling of wheat, like bran) and cover with a paper bag to keep flies away. (The Complete Grazier, 1830: 304)
In warm weather, make sure that the blood is all drained from the meat and the meat is rubbed with fine salt before the brine is poured over. (The Complete Grazier, 1830: 304)
Remember that wet-cure is more expensive than dry cure unless the brine is re-used. Our farmer states that brine is re-used “with advantage”. Before it is re-used, the old brine must be boiled first and water and the other ingredients must be added proportionately. (The Complete Grazier, 1830: 304)
It is this old brine or re-used brine that became the cornerstone of the industrial bacon curing plants in Denmark and which they call the “mother brine”. Needle injection of meat along with the faster curing action of the mother brine would become the key feature of curing plants in Denmark and would later be adopted by factories around the world. It was the fastest way of producing bacon and was remarkably effective.
Wet-curing in combination with injection (brine cure – with pumping)
In Denmark, during the 1800’s, a wet curing method was invented using a combination of stitch pumping and curing the meat in curing tanks with a cover brine. (Wilson, W, 2005: 219) Brine consisting of nitrate, salt and sugar were injected into the meat with a single needle attached to a hand pump (stitch pumping). Stitch pumping was either developed by Prof. Morgan, whom we looked at earlier or was a progression from his arterial injection method.
The meat was then placed in a mother brine mix consisting of old, used brine and new brine. The old brine contained the nitrate which was reduced through bacterial action into nitrite. It was the nitrite that was responsible for the quick curing of the meat.
Denmark was, as it is to this day, one of the largest exporters of pork and bacon to England. The wholesale involvement of the Danes in the English market made it inevitable that a bacon curer from Denmark must have found his way to Calne in Wiltshire and the Harris bacon factories. The tank-cured method, as it became known, was adopted by C & T Harris.
A major advantage of this method is the speed with which curing is done compared with the dry salt process previously practiced. Wet tank-curing is more suited for the industrialisation of bacon curing with the added cost advantage of re-using some of the brine. It allows for the use of even less salt compared to older curing methods.
Clues to the date of the Danish invention come to us from newspaper reports about the only independent farmer-owned Pig Factory in Britain of that time, the St. Edmunds Bacon Factory Ltd. in Elmswell. The factory was set up in 1911. According to an article from the East Anglia Life, April 1964, they learned and practiced what at first was known as the Danish method of curing bacon and later became known as tank-curing or Wiltshire cure.
A person was sent from the UK to Denmark in 1910 to learn the new Danish Method. (elmswell-history.org.uk) The Danish method involved the Danish cooperative method of pork production founded by Peter Bojsen on 14 July 1887 in Horsens. (Horsensleksikon.dk. Horsens Andelssvineslagteri)
The East Anglia Life report from April 1964, talked about a “new Danish” method. The “new” aspect in 1910 and 1911 was undoubtedly the tank curing method. Another account from England puts the Danish invention of tank curing early in the 1900’s. C. & T. Harris from Wiltshire, UK, switched from dry curing to the Danish method during this time. In a private communication between myself and the curator of the Calne Heritage Centre, Susan Boddington, about John Bromham who started working in the Harris factory in 1920 and became assistant to the chief engineer, she writes: “John Bromham wrote his account around 1986, but as he started in the factory in 1920 his memory went back to a time not long after Harris had switched over to this wet cure.” So, early in the 1900’s, probably sometime between 1899 and 1910, the Danes invented and practiced tank-curing which was brought to England around 1911.
It only stands to reason that the power of “old brine” must have been known from early after wet curing and needle injection of brine into meat was invented around the 1850’s by Morgan. Before the bacterial mechanism behind the reduction was understood, butchers must have noted that the meat juices coming out of the meat during dry curing had special “curing power”. It was, however, the Danes who took this practical knowledge, undoubtedly combined it with the scientific knowledge of the time and created the commercial process of tank-curing which later became known as Wiltshire cure.
Multi-Needle Injection and Vacuum Tumbling
The composition of the brine changed around 1915 by the direct addition of sodium nitrite. Multi-needle injectors and vacuum tumblers are commonly used in combination in modern meat curing plants around the world.
It is generally accepted that these developments took place in the mid to late 1900’s, but an interesting US patent (number 23,141) was awarded to L. M. Schlarb from Allegheny, Pennsylvania on 3 June 1901 directly related to injection and vacuum machines for meat curing. (Journal of the Society of Chemical Industry; 1902: 269)
The process is described as “injecting brine and carbon dioxide under pressure into the meat by means of suitable needles connected to a tank containing the brine and carbon dioxide, the pressure in the tank being about 2 atmospheres.” The nozzles it talks about maybe the three needle injectors that were used until the middle of the 1900’s and the unique aspect of the patent was the use of brine in conjunction with carbon dioxide. (Journal of the Society of Chemical Industry; 1902: 269)
The next bit is fascinating as it is possibly the earliest recorded date of the use of a vacuum machine in meat processing. The patent is described in a journal article that “the meat is now placed in a vessel from which the air is exhausted, and brine is then allowed to flow in. The meat is allowed to remain in the brine for about 10 hours, and may then be subjected to the action of carbon dioxide under pressure.” If one removes the presence of carbon dioxide, it is then reasonable to assume that a vacuum machine has been in use in one shape or another to facilitate the diffusion of brine into meat, as early as 1901 and probably earlier. (Journal of the Society of Chemical Industry; 1902: 269)
Over the next 60 years, the multi-needle injector became bigger, with more needles until the present machines were being produced from the mid-1900’s. Tumbling machines, as we know it today has been in use from the early 1970’s.
The biggest development in commercial curing plants of the last decade is undoubtedly the introduction of what we call the grid system. According to this method, grids or bacon moulds are used to give the bacon a regular shape. The meat is normally wrapped in banking paper before it is placed in the moulds and in one form or the other, an enzyme, Transglutaminase, is incorporated added to the product. The main purpose of this is to achieve higher slicing yields, but in reality, it also accounts for lower smoking losses. A detailed treatment of this method can be found at Restructuring of whole muscle meat with Microbial Transglutaminase – a holistic and collaborative approach. As the name of the article indicated, I am inviting producers to who are interested to interact with me on the process as long as developments will be used for our mutual benefit.
As far as brine technology is concerned, a host of brines has seen the light which claims to be natural and nitrite-free. I remain very skeptical about these and refer you to Mechanisms of Meat Curing. The only compound that I have ever tested that accomplish nitrite or nitrate free is sal ammoniac and tests are still underway to develop this into a commercially viable proposition that will be accepted by the public who have demonstrated an aversion against the use of ammonia in curing, more so than against nitrite.
This review is done from the perspective of a commercial mainstream high throughput bacon plant. It, however, paints a rich picture and most of what is regarded as “artisan” today has been the way that large throughput factories of yesteryear have done it. In years to come, how bacon was cured even when we embarked on our current bacon project in 2008 will be regarded as “artisan curing” as we have seen the transition to moulds or grid curing over the last 10 years.
Consumer demands, perceptions and technology will remain the driving force behind this fascinating industry. Many aspects will have to be added to this review article such as change to health concerns and this changed the methods and ingredients over the years. As time allows, I will add these.
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Figure 1: Founders of bacon plant: http://www.elmswell-history.org.uk/arch/firms/baconfactory/article2.html
Figure 2: Stitch pumping, http://www.suffolkheritagedirect.org.uk/resources/tours/made-in-suffolk.html