Chapter 08.08 Von Liebig and the Theory of Proteins of Gerard Mulder.

Bacon & the Art of Living 1

Introduction to Bacon & the Art of Living

The quest to understand how great bacon is made takes me around the world and through epic adventures. I tell the story by changing the setting from the 2000s to the late 1800s when much of the technology behind bacon curing was unraveled. I weave into the mix beautiful stories of Cape Town and use mostly my family as the other characters besides me and Oscar and Uncle Jeppe from Denmark, a good friend and someone to whom I owe much gratitude! A man who knows bacon! Most other characters have a real basis in history and I describe actual events and personal experiences set in a different historical context.

The cast I use to mould the story into is letters I wrote home during my travels.


Von Liebig and the Theory of Proteins of Gerard Mulder

Copenhagen, September 1891

Dear kids,

It is the first day of autumn. Denmark is not home, but there is a beauty to this world. Copenhagen is an amazingly beautiful city. It is much smaller than I thought it would be, but it is very organised. The buildings are old and beautiful!

Andreas became a brother. He is an amazing soccer player. I can’t keep up with him, either when I play with or against him. I try to teach them to play cricket and rugby, but it is difficult. I have given up, to the great amusement of his dad (and the relief of Andreas).

Even autumn is colder than the coldest winters we have in Cape Town. As the cold sets in I miss you guys more every day. My only consolation is that Minette is here! Every week we make time to go on a long hike.  How I miss Table Mountain!  I miss my mom.  To sit at the kitchen table as she cooks one of her legendary lunches!  I miss my dad.  I miss Oscar and our crazy late-night dreaming. The fact that I learn on the one hand and do when I work in the bacon factory makes the learning more effective.

Copenhagen Harbour. The new Frihavns must impressive building was Silo warehouse on Midtermolen, built in 1892-94 by William Dahlerup
The Copenhagen harbour. The new Frihavns’ most impressive building was the Silo warehouse on Midtermolen, built in 1892-94 by William Dahlerup.

Copenhagen is not Africa!  It seems to me that all great dreams begin on horseback, on a farm, looking for stray cattle. The vlaktes of the Wes Transvaal seem so far. Like a dream.  I remember the day after we tasted the pork that we tried to cure on Oscar’s farm with the saltpeter that we bought from the Danish spice trader in Johannesburg and discovered that the pork was off. We tried to do it according to the Danish curing system as it was explained to us.  We were so disappointed!  Trudie told us that we must have done something wrong. We were sure that we did everything that the Danish guy told us.

The next day Ou Jantjie came to the house and told us that he saw some of Oscar’s cattle on Atties farm, close to the dam, nearest to Atties house. The off-tasting pork was out of our minds and we were on Poon and Lady, riding to look for the cattle.

Oscar said that Trudie is right. That we must have done something wrong and that we must learn much more.  I think he knew from the beginning how difficult it would be to take David de Villiers Graaff on when it comes to curing bacon. Oscar’s mind is fast.

I reminded him that the spice trader said that if we really want to learn how it’s done, that we must get on the next steamship leaving the Cape for Copenhagen. We decided to get everybody who will support the dream together for a meeting at his house one evening. Then we will decide.

The wind was in our faces and we had great dreams. I am learning how important those initial dreams are.  It is like building up steam pressure before the engine starts to turn the big pistons on a steamship.  If the pressure is not build up first, it will never be enough for the first “turn”. As soon as its turning, momentum takes over and the engine takes on a life of its own.  The initial dreams are the building up of pressure.

This art of curing meat has been developing over thousands of years. On the one hand, people wanted to prevent meat from spoiling and on the other hand, cured meat developed into a culinary delicacy. The key ingredient is saltpeter (1).

Jeppe and I have the best of times during lunchtime.  Since Minette arrived, it gave our lunchtime lessons a dynamic character. He would go through the relevant scientific discoveries of the previous few years, pointing out the direct application on the science and art of curing bacon.  The science and history lessons give both Minette and me enjoyment that is hard to communicate.  The Wednesday, following our visit to the University, the Chemistry Professor decided to visit us at the bacon factory.  It set the stage for another volcanic afternoon!

Justus von Liebig

He did not want to leave us “hanging in the air”, so to speak by not completing his private lecture about the development of protein metabolism events Germany and the invention of the theory of proteins.  We were ready with notebooks, pens, and inquiring minds!  The focus now shifted from the French to the German schools. Our attention shifts to the formidable scientist in the person of Justus von Liebig.  His father was a chemical manufacturer and had a small laboratory attached to his shop.  Here Justus loved performing experiments and an exceptional life was inspired.  After studying pharmacy, he received a doctorate from the University of Erlangen in Bavaria in 1822.  The Grand Duke of Hesse-Darmstadt and his ministers noticed him and funded his further studies in chemistry under Joseph-Louis Gay-Lussac in Paris between 1822 and 1824.  Gay-Lussac himself found all plant seeds “contain a principle abounding in azote.”  It was, in Paris when a meeting with Alexander von Humboldt, according to Von Liebig, set his career on the path it took.  Up to that point, it was the French chemists who were responsible for the progression of protein metabolism, but with Von Liebig, this was about to change.

Humboldt is one of my heroes and as a child, I practically committed his books to memory.   Humboldt arranged an appointment for Von Liebig at the small University of Giessen in May 1824. Liebig wrote about this meeting  that “at a larger university, or in a larger place, my energies would have been divided and dissipated, and it would have been much more difficult, perhaps impossible, to reach the goal at which I aimed.”  Applying the techniques that he learned under Gay-Lussac he changed the face of organic chemistry and became the father of agricultural chemistry. The study of protein metabolism was now firmly in the hands of the Germans.

At the University of Giessen, Liebig created the most productive school of organic chemistry in existence at the time.  He perceived that his work could be logically extended to the chemistry of the living body. In 1840 his book, “Thierchemie in Ihrer Aufwendung auf Physio logie” appeared, and an English translation of the work entitled “Animal Chemistry, or Organic Chemistry in its Applications to Physiology and Pathology” appeared 1842.  Liebig believed that the basis of protein metabolism was chemical.  Some believe this is his most important contribution to the subject.

Von Liebig was well prepared to make such a contribution on account of his training in France and his own studies in organic chemistry. The Danish Chemistry professor brought Von Liebig’s work, Animal Chemistry (1842) along and quoted liberally from us to show the various aspects of Liebigs views on protein metabolism.  He wrote (p. 40):

“… If we hold that increase of mass in the animal body, that development of its organs, and the supply of waste,—that all this is dependent on the blood, that is, on the ingredients of the blood, then only those substances can properly be called nutritious and considered as food which are capable of conversion into blood. To determine, therefore, what substances are capable of affording nourishment, it is only necessary to ascertain the composition of the food, and to compare it with that of the ingredients of the blood. Two substances require special consideration as the chief ingredients of the blood: . . . fibrine, which is identical in all its properties with muscular fibre, when the latter is purified from all foreign matters. The second principal ingredient of the blood is contained in the serum, and gives to this liquid all the properties of the white of eggs, with which it is identical. When heated, it coagulates into a white elastic mass, and the coagulating substance is called albumen. Fibrine and albumen, the chief ingredients of blood, contain, in all, seven chemical constituents, among which nitrogen, phosphorus, and sulphur are found. . . . Chemical analysis has led to the remarkable result that fibrine and albumen contain the same organic elements united in the same proportion…. In these two ingredients of blood the particles are arranged in a different order, as shown by the difference of their external properties; but in chemical composition in the ultimate proportion of the organic elements, they are identical. . . . Both albumen and fibrine, in the process of nutrition, are capable of being converted into muscular fibre, and muscular fibre is capable of being reconverted into blood. . . . All part of the animal body which have a decided shape, which form parts of organs, contain nitrogen; all of them likewise contain carbon and the elements of water. . . The chief ingredients of the blood contain nearly 17% of nitrogen and no part of an organ contains less than 17% nitrogen.”

“The most convincing experiments and observations have proved that the animal body is absolutely incapable of producing an elementary body, such as carbon or nitrogen, out of substances which do not contain it; it obviously follows, that all kinds of food fit for the production either of blood, or of cellular tissue, membranes, skin, hair, muscular fibre, etc. must contain a certain amount of nitrogen, because that element is essential to the composition of the above-named organs; because the organs cannot create it from the other elements presented to them; and, finally, because no nitrogen is absorbed from the atmosphere in the vital process.”

“The nutritive process in the carnivora is seen in its simplest form. This class of animals lives on the blood and flesh of the graminivora; but this blood and flesh is, in all its properties, identical with their own. . . . In a chemical sense, therefore, it may be said that a carnivorous animal, in supporting the vital process, consumes itself. That which serves for its nutrition is identical with those parts of its organisation which are to be renewed. The process of nutrition in graminivorous animals appears at first sight altogether different. Their digestive organs are less simple, and their food constituents consist of vegetables, the great mass of which contains but little nitrogen. … Chemical researches have shown, that all such parts of vegetables as can afford nutriment to animals contain certain constituents which are rich in nitrogen; and the most ordinary experience proves that animals require for their support and nutrition less of these parts of plants in proportion as they abound in the nitrogenised constituents. Animals cannot be fed on matters destitute of these nitrogenised constituents. . . . These nitrogenised forms of nutriment in the vegetable kingdom may be reduced to three substances, which are easily distinguished by their external characters. Two of them are soluble in water. The third is insoluble.”

He then states that he recognises “a vegetable fibrin, vegetable albumin and vegetable casein” which is similar in characteristics to these animal products.  He continues (p. 48):  “How beautifully and admirably simple, with the aid of these discoveries, appears the process of nutrition in animals, the formation of their organs, in which vitality chiefly resides! Those vegetable principles, which in animals are used to form blood, contain the chief constituents of blood, fibrine and albumen, ready formed, as far as regards their composition. . . . From what has been said, it follows that the development of the animal organism and its growth are dependent on the reception of certain principles identical with the chief constituents of blood.”

Liebig’s view on nitrogen in nutrition is summarized by himself as follows (p. 95): . . . “According to what has been laid down in the preceding pages, the substances of which the food of man is composed may be divided into two classes; into nitrogenised and non-nitrogenised. The former are capable of conversion into blood; the latter incapable of this transformation. Out of those substances which are adapted to the formation of blood are formed all the organised tissues. The other class of substances, in the normal state of health, serve to support the process of respiration. The former may be called the plastic elements of nutrition; the latter, elements of respiration. Among the former, we reckon—vegetable fibrine, vegetable albumen, vegetable caseine, animal flesh, animal blood. Among the elements of respiration in our food are—fat, starch, gum, cane sugar, grape sugar, sugar of milk, pectine, bassorine, wine, beer, spirits.”

You will see that none of Von Liebig’s views were new.  These were concepts that originated with Magendie, 25 years earlier.  Note in particular that Von Liebig did not have an inkling of the possibility of digestion and reconstruction of proteins taken in the diet.  (Munro and Allison, 1964)

One of the many productive directions of the work of Von Liebig and his students was the application of oxidizing agents (example, manganese dioxide, and chromic acid) during acid hydrolysis of proteins and in the process identifying a series of acids and aldehydes. The concept of studying the degradation products of protein originated with Von Liebig and was to play a crucial role in the next generation  (Sahyun, M. (Editor). 1948) There is an interesting point of application of this work to the modern bacon curer.  It has emerged that there is a link between foaming and the length of the amino acids that remain after proteins have been “digested” with the aid of an acid.  This became clear when we tried to dissolve the result of our “digestion experiments” in water.  If for some reason, such “digested” proteins must be used in a bacon brine, if the foaming is excessive and interferes with the curing operation, it will be of great help to “digest” the proteins for longer before it is recovered and hydrated.

The atomic theory

At this point the Chemistry professor paused.  He asked how much we know about Dalton’s atomic theory.  Of course, I knew it well from high school in Cape Town.

I was very surprised when the professor said that Dalton’s work had an important application in the field of nutritional studies. John Dalton was by all accounts not the brightest of students.  Some said that his main characteristic was not being bright but rather, determination.   He was poor and largely self-taught.  He worked as a  schoolmaster in the north of England and developed a very important notion. The notion was that all of the elements are made up of indivisible particles, or “atoms,” and, importantly, that for each element, every atom is identical.  He came to the conclusion that in chemical combinations, two or more different atoms come together to form a firm union and this union, was, as far as the new substance is concerned, always in the same simple ratios by weight.   So, for example, the gas, carbon dioxide has exactly twice the weight of oxygen (by unit weight of carbon) compared to what is present in another gas called carbon monoxide.  So, the different elements in any compound are fixed.  When comparing two different compounds, the same two elements will always be in a simple ratio by weight.

He further concluded that when gasses combine, they always do so in the same simple relation by volume.  Let’s take the formation of ammonia as an example.  When it is formed, 3 volumes of hydrogen combine with 1 volume of nitrogen and they form exactly 2 volumes of ammonia gas.

A conclusion from these is that equal volumes of different gases contain the same numbers of molecules if one sees that many elements, such as hydrogen, oxygen, and nitrogen, have two atoms combined together to form a single molecule.

Early on there was uncertainty if carbon and oxygen each have one-half of the atomic weights that we now assign to them.  Prout in England used improved methods of analysis and arrived at the formula C2H4N2O2.  Double the atomic weights for C and O and you arrive at the modern formula of CH4N2O.

In the early 1800s, Friedrich Wöhler achieved what may believe to the start of organic chemistry when he obtained urea by heating silver cyanate with ammonium chloride. He wrote to his professor: “I can make urea without the use of kidneys.”  By doing this, he demonstrated that an organic compound produced in living systems could also be produced in the laboratory without the aid of any “vital force.”

Wöhler and Von Liebig’s Free Radical

Wöhler worked with Liebig and developed the idea of a common radical that would combine with other reagents, but still retain its own nature and be recoverable by further reactions.  In chemistry, a free radical  is a species that contain one occupied orbital.  A characteristic of a free radical is that they are neutral and they tend to be highly reactive.  The first such ree radical was “benzoyl”.

Starting with benzaldehyde (C6H5CHO), it can be oxidize to benzoic acid (C6H5CO2H).  Note the addition of an oxygen atom.  Alternatively, a chlorinated derivative can be formed.  The original benzaldehyde can be created by reducing or removing oxygen.”  (Carpenter, 2003)  It is easy to see the similarity in what we are doing with nitrate, nitrate, and ammonia and this, in turn, is build upon the logic of the atomic theory.

Gerard Mulder and the nature of animal substance

The Dutch chemist Gerard Mulder (1802–1880) published a paper in a Dutch journal in 1838 which was reprinted in 1839 in the Journal für praktische Chemie. Mulder examined a series of nitrogen-rich organic compounds, including fibrin, egg albumin, gluten, etc., and had concluded that they all contained a basic nitrogenous component (~16%)  to which he gave the name of “protein” (Munro and Allison, 1964) from a Greek term implying that it was the primary material of the animal kingdom.

The term protein was coined by Jöns Jacob Berzelius, and suggested it to Mulder who was the first one to use it in a published article. (Bulletin des Sciences Physiques et Naturelles en Néerlande (1838); Hartley, Harold (1951) “Ueber die Zusammensetzung einiger thierischen Substanzen” 1839)). Berzelius suggested the word to Mulder in a letter from Stockholm on 10 July 1838. (Vickery, H, B, 1950) Mulder suggested using the symbol “Pr” for the radical, that egg albumin could be expressed as “Pr10 · SP” and serum albumin as “Pr10 · S2P,” and that the radical itself had the molecular formula “C40H62N10O12.  (Carpenter, 2003)

This common nucleus was linked with phosphorus and sulfur to give the various compounds referred to above. “Die organische Substanz, welche in allen Bestandtheilen des thier ischen Körpers, so wie auch, wie wir bald sehen, im Pflanzenreiche Vorkommt, könnte Protein von Tporetos primarius, genannt werden. Der Faserstoff und Eiweissstoff der Eierhaben also die Formel Pr + SP, der Eiweissstoff des Serums Pr + SP.” (The organic substance which is found in all the constituents of the animal body, as well as, as we shall soon see, in the vegetable kingdom, might be called protein of Tporetos primarius. The fiber and protein of the eggs thus have the formula Pr + SP, the protein of the serum Pr + SP)  (Munro and Allison, 1964)

Liebig initially liked the concept.  He wrote, “… When animal albumen, fibrine, and caseine are dissolved in a moderately strong solution of caustic potash, and the solution is exposed for some time to a high temperature, these substances are decomposed. The addition of acetic acid to the solution causes, in all three, the separation of a gelatinous translucent precipitate, which has exactly the same characters and composition, from whichever of the three substances above mentioned it has been obtained. Mulder, to whom we owe the discovery of this compound, found, by exact and careful analysis, that it contains the same organic elements, and exactly the same proportion, as the animal matters from which it is prepared; insomuch, that if we deduct from the analysis of albumen, fibrine, and caseine, the ashes they yield, when incinerated, as well as the sulphur and phosphorus they contain, and then calculate the remainder for 100 parts, we obtain the same result as in the analysis of the precipitate above described, prepared by potash, which is free from inorganic matter.”  (Munro and Allison, 1964)

If we look at it in this way, the main ingredients of blood and caseine in milk can be regarded as a mixture of phosphates and other salts, and of sulphur and phosphorus, with a compound of carbon, nitrogen, and oxygen, in which the relative proportion of these elements is fixed.  This compound can then be regarded as the commencement and starting-point of all other animal tissues because these are all produced from the blood. Mulder had an insight that since the insoluble nitrogenised part of wheat flour (vegetable fibrine) when treated with potash, the exact same product is yielded namely protein.  He found that the true starting-point for all the tissues is albumen and that all nitrogenised articles of food, whether derived from the animal or from the vegetable kingdom, are converted into albumen before they can take part in the process of nutrition.  Liebig, like Mulder, ascribes the formula C4s H36N6O14 to protein, and albumen becomes C18H38N6014 + P + S, fibrine is C48E36. N6014 + P + 2 S, and so on.

– Liebig’s Opposition

Liebig eventually rejected Mulder’s concept of a nucleus protein based on work he continued to do on protein chemistry. He sets forth his arguments against Mulder at some length in his book “Researches on the Chemistry of Food,” published in an English edition in 1847. Here Liebig indicates that several chemists were unable to repeat some of Mulder’s basic experiments and that his formulas for fibrin, albumin, etc., as compounds of protein with sulfur and phosphorus in specific relations, do not agree with the results of more recent analyses of these substances. In this, he conveniently forgets his own earlier enthusiasm for Mulder’s view, and says (p. 18): “… A theoretical view in natural science is never absolutely true, it is only true for the period during which it prevails; it is the nearest and most exact expression of the knowledge and the observations of that period. It ceases to be true for a later period, inasmuch as a number of newly acquired facts can no longer be included in it. . . . But the case is very different with the so-called proteine theory, which cannot be regarded as one of the theoretical views just mentioned, since, being supported by observations both erroneous in themselves and misinterpreted as to their significance, it had no foundation in itself, and was never regarded, by those intimately acquainted with its chemical groundwork, as an expression of the knowledge of a given period.” (Munro and Allison, 1964). “Mulder was enraged by the tone of the criticism from Liebig, who was now denying what he himself had previously asserted.” (Carpenter, 2003)

Despite his criticism, Von Liebig suggests the direction which eventually led researchers to ultimately resolved the structure of the protein molecule.

He says (p. 27) : … The study of the products, which caseine yields when acted on by concentrated hydrochloric acid, of which, as Bopp had found, Tyrosine and Leucine constitute the chief part, and the accurate determination of the products which the blood constituents, caseine, and gelatine, yield when oxidised, among which the most remarkable are oil of bitter almonds, butyric acid, aldehyde, butyric aldehyde, valerianic acid, valeronitrile, and valeracetonitrile, have opened up a new and fertile field of research into numberless relations of the food to the digestive process, and into the action of remedies in morbid conditions.” (Munro and Allison, 1964)

It is an interesting thought that in the word “protein” we refer to the important class of body constituents, and we, at the same time, commemorate an erroneous oversimplification of protein structure.  We must also remember that we use the word in a meaning different from that originally intended. The German word for protein is “Eiweiss.” The reason may very well be because of Von Liebig’s eventual rejection of Mulder’s hypothesis.” (Munro and Allison, 1964). Dennis M Bier states that despite these nuances, Berzelius and Mulder were, in the most basic analysis, right: “Protein is the essential general principle of the constituents of the animal body. Thus, one might briefly summarize the physiological roles of protein in metabolism as “responsible for just about everything.” (Bier, D. M., 1999). “The notion of the protein radical disappeared from the literature and the term “protein” gradually began to be applied to all the materials previously described as “animal substance.”   (Carpenter, 2003)

Is Protein the only true nutrient?

Our good professor was on a roll.  Nitrogen, as the key nutrient was firmly established, but is this the only one?  While he is on the subject, he gave us a history lesson on the further development of thoughts around this matter.  As a food producer, this remains one of the overall biggest subjects.  Nutrition!  It is the original and main reason why we eat!

Von Liebig wrote the following in his book, Animal Chemistry or Organic Chemistry in its Application to Physiology and Pathology, that “because his analyses of muscles failed to show the presence of any fat or carbohydrate, the energy needed for their contraction must come from an explosive breakdown of the protein molecules themselves, resulting in the production and excretion of urea. Protein was, therefore, the only true nutrient, providing both the machinery of the body and the fuel for its work.

What is the reason then that we would need the other parts of the food that we consume?   Why is carbonic acid produced in much higher volumes during exercise? The explanation of Von Liebig was that increased respiration was needed to keep the heart and other tissues from overheating. This led to more oxygen finding a way into the tissues, which unfortunately potentially cause oxidative damage and a loss of protein tissue. Fats and carbohydrates then acted as mopping agents of this excess by being themselves preferentially oxidized.

Von Liebig’s book quickly gained a reputation as an important intellectual synthesis.  His ideas gained wide acceptance, the influence which was felt for many years. The Professor of Medicine at Edinburgh University was, for example, asked to investigate an unexpected and very serious outbreak of scurvy in a Scottish prison, he immediately concluded that it must be the result of an inadequate intake of protein. He calculated the average daily protein intake of a prisoner to be an ample 135g. Only 15g of this was from animal sources and 102g from gluten.

His conclusion was to raise the average daily intake of milk to increase the intake of animal protein because, he argued, the power of the body to convert gluten to animal protein was limited.  There were, however, a problem with this logic, as was spotted and pointed out by another Scottish physician who replied that the value of lemon juice in the prevention of scurvy was well established and could not possibly be attributed to its protein content, given that a curative dose contained only a negligible amount of nitrogen.

The theory that muscular work is required to break protein down was problematic.  The traditional diet of laborers was of lower protein content that of the less active rich. Now, remember the book, Foods, we are reading every night with Andreas and his family.  Edward Smith, the author, and a British physician, and physiologist is another scietist of the time who was interested in the welfare of prisoners.  He was worried about the stressfulness of them having to work on a treadmill.  He measured their urea excretion in the 24h during and after their 8 hours of work, and again on their subsequent rest days, and found no difference. His findings were in complete opposition to the position of Von Liebig who would have said that on the basis that the energy expended all came from the breakdown of protein that resulted in the production of urea.  (Carpenter, 2003)

Liebig and Urine

Von Liebig drew attention to urea as an end-product of protein breakdown in the body.  He did not get it right completely.  In his work, “Animal Chemistry” (1842), (p. 62) he wrote, “… We know that the urine of dogs, fed for three weeks exclusively on pure sugar, contains as much of the most highly nitrogenised constituent, urea, as in the normal condition. Differences in the quantity of urea secreted in these and similar experiments are explained by the condition of the animal in regard to the amount of the natural motions permitted. Every motion increases the amount of organised tissue that undergoes metamorphosis. Thus, after a walk, the secretion of urine in man is invariably increased.”

Later (p. 245), he wrote, “The amount of tissue metamorphosed in a given time may be measured by the quantity of nitrogen in the urine.” All this shows Von Liebig’s central thought that protein in muscle was the fuel for muscular exercise.  He believed that the nitrogenous components of the diet must first be converted to living tissue before being broken down to yield urea. “There can be no greater contradiction, with regard to the nutritive process, than to suppose that the nitrogen of the food can pass into the urine as urea, without having previously become part of an organized tissue.” (p. 144).” (Munro and Allison, 1964)

Liebig’s Contribution to Protein Metabolism and the work of Carl Voit

Why this attention to Von Liebig?  It appears from what we have seen that he did not contribute much of permanent value to our understanding of protein metabolism. Nothing could be further from the truth.  Von Liebig adhered to a vigorous application of organic analysis to compounds of biological interest, he undoubtedly laid the foundations of intermediary metabolism and much of the important work that followed Von Liebig was predicated on these findings. Besides these, Von Liebig identified many of the compounds of biological interest which subsequent researchers made their focus areas with great success.

Von Liebig’s ultimate genius was that he took on seemingly insurmountable problems and even though he did not come up with the ultimate solutions, he managed to break the issues down to such an extent that one can say he pointed the way to their ultimate solution. Look for example at his comments on intermediary metabolism.  He wrote (“Researches on the Chemistry of Food,” (1847) p. 10): “The intermediary members of the almost infinite series of compounds which must connect Urea and Uric acid with the constituents of the food, are, with the exception of a few products derived from the bile, almost entirely unknown to us; and yet each individual member of this series, considered by itself, inasmuch as it subserves certain vital purposes, must be of the utmost importance in regard to the explanation of the vital processes, or of the action of remedies.”

Another good example is the fact that he saw certain chemical reactions as only occurring in biological systems and suspected that these were dependent on the presence of proteins. Have a look at the following statement (p. 7) from his book on food chemistry where he came agonizingly close to our modern understanding of the concept of enzymes:  “… There is, probably, no fact more firmly established as to its chemical signification, than this, that the chief constituents of the animal body, albumen, fibrine, the gelatinous tissues, and caseous matter, when their elements are in a state of motion, that is, of separation, exert on all substances which serve as food for men and animals, a defined action, the visible sign of which is a chemical alteration of the substance brought in contact with them. That the elements of sugar, of sugar of milk, or starch, etc., in contact with the sulphurised and nitrogenised constituents of the body, or with analogous compounds which occur in plants, when these are in a state of decomposition, are subjected to a new arrangement and that new products are formed from them, most of which cannot be produced by chemical affinities, this is a fact, independent of all theory.”

Von Liebig’s greatest contribution to the development of protein metabolism is in the school of biochemical studies, founded by him.  This was done first in Giessen, and later in Munich, where he became professor of chemistry in 1852. From here emerged a number of very important proponents of metabolism, chief among them being Carl Voit, whose researches in protein metabolism placed the concept of nitrogen balance on a firm footing.

Voit was intensely interested in “animal chemistry.” He wrote that Dumas was wrong in his assertions since it was well known that pigs would fatten when fed on potatoes that were rich in starch, but had only a small amount of fat. Accordingly, it must be concluded that animals are able to convert carbohydrates to fat even though the conversion required “reduction” rather than oxidation.

French researchers who were regarded as the authorities on this subject challenged this view, and Boussingault put the matter to the test.   He performed another groundbreaking experiment with pigs.  He took a young pig and killed it and analysed its carcass.  He took a littermate of this pig, of the same weight, and fed it measured amounts of feed for another 3 months. The carcass analysis of the second pig indicated that this pig had an extra 13.6kg fat but the feed it consumed only had 6.8kg.

This very clearly showed the French school to be wrong on this point.  Both Boussingault and Dumas retired from working with animals.  Von Liebig became the new authority, even though he had never actually carried out a feeding trial. He continued to advocate his ideas on physiology and nutrition. Most of these were gradually shown to have been completely wrong, but at least they stimulated others to do research, putting them to the test.”  (Munro and Allison, 1964)

An Inspirational Message

Kids, take note that neither Mulder nor Von Liebig illuminated protein or its metabolism fully, but we gain a great appreciation for their work in the early to mid-1800s. I wonder how many of today’s researchers would do as much as these men did with the scant knowledge they had and it is a lesson to us all. Rigour in our work will yield results, no matter how tentative at first.  It reminds me of the old verse from Sunday school in the Groote Kerk in Cape Town that there is profit in all labour.

I think that there can be no doubt that nitrogen is absolutely key to the art of bacon curing and the most important macro molecule we are working with is protein.  I came to realise that bacon is nothing less than the art of manipulating it.  A question of whether the nitrogen that we add to the meat in the form of nitrate or nitrite is good for us or not is in the first instance the wrong question since when you are talking about protein you are talking about nitrogen and vice versa.

Thirdly to nitrogen and protein is the concept of nutrition.  Yes, we eat because we are social animals and there is nothing more sociable than a great meal.  We eat because we listen to bach and drink pilsner.  We enjoy it!  But most importantly, we eat because it keeps us healthy and it contains the fuel we need every day to live and breathe and have our being.  Nutrition is of the absolute greatest importance when we produce food.

The development of the art of meat curing and understanding its chemistry and processes is intimately connected to our most basic understanding of life itself.

I am downstairs in the living room.  Minette passed ut on the couch – she is exhausted.  I’m finishing up and then we will all go to bed.

I love you more than life itself!

Your Dad.


Practical Applications for the Modern Bacon Curer

In bacon production, one determines the total meat content as follows.  Assume you start with 100kg of meat and inject 20L brine.

Meat weight:  100kg
Brine added:  + 20L (100kg becomes 120kg; added through injection/ tumbling)
Loose 10% in cooking/ smoking: – 12kg (120kg becomes 108kg)
Freezing loss of -1%: – 1.08kg yields total bacon ready for slicing: 106.92kg.

Divide the meat weight you started with by the end weight after processing (100/106.92) = 93.52% total meat content.

According to SA regulations, bacon must be at least 95% total meat content.

One doesn’t lose proteins during steam cooking. Only during water cooking. In the older literature on the subject, when they talk about curing, they mean salt only curing as in dry-curing and in this process there is a loss of proteins (if done in the traditional way of turning the meat every day and allowing the extracted meat juices to run off). If one, however, cooks the bacon, as in Australia, during the cooking step, fat will melt and drip off. Exactly how much fat is lost is determined through analysis. I am sure the % is small, but surprising results are obtained through analysis.

It will impact the calculation since total meat is defined as lean meat plus fat. Meat weight after the actually visible fat has been trimmed off x 0.9 is a good approximation to determine actual lean meat content. All meat contains fat that can not be seen. Without it, meat will be completely un-edible. Two further ratios we want to become familiar with are the ratio of percentage protein nitrogen to lean meat % being N x 30 = lean meat % and the nitrogen to protein factor which is 6.25 meaning N x 6.25 = total protein.

These ratios are important for meat processors.   Let’s look at our calculation again which we used above.  Note that they only achieve total meat content of 93% in their bacon and they need to have it at 95% or above.  They can now do the following:

Meat weight:  100kg
Brine added:  + 20L (100kg becomes 120kg; added through injection)

In the tumbling stage, add 1kg of pork protein (80% actual protein – the other 20% will be a filler).  Of course, various levels of functionality are commercially available and one must inquire of what the actual protein percentage is to complete the calculation.  This means that the nitrogen added in our example of a product with an 80% functionality is 80% x 1kg = 0.800kg protein / 6.25 – the nitrogen-to-protein ratio to give us the weight of the protein nitrogen x 30 – the protein-to-lean-meat factor = 3.84kg lean meat. In other words, by adding 800g functional protein, they have effectively added 3.84kg to the starting meat weight as lean meat.  There is no fat since the added functional pork proteins do not contain fat.

They can then use their starting ratio as 100kg + 3.84kg = 103.84 which, after injection and tumbling will yield them 106.92.  Dividing the meat weight you started with by the end weight after processing is now 103.84/ 106.9 = 97.1% total meat content which, if this is in SA, places you well within the legal requirements for bacon.

For those interested in having this in a live spreadsheet I include this sheet, courtesy of Dr. Francois Mellett. ED2-8 Cost op Protein, LME, and TME.  Here he compares the cost of different protein sources and uses the conversion factor of 4.8 to move between % protein and TME/ LME.  He derives his conversion factor of 4.8 to move between % protein and LME eqw as follows:  The two equations he works with are:

Protein Nitrogen x 6.25 = Proteins

Percentage Lean Meat = (Percentage Protein Nitrogen × 30 )

Let’s take TVP Soy with a protein content of 50%.  Therefore:

Protein Nitrogen x 6.25 = 50%; Protein Nitrogen % = 50%/6.25 = 8

Percentage Lean Meat = (8 × 30 ) = 240/100 = 2.4.

The same can be achieved by the factor 30/6.25 = 4.8; 4.8 x 50% = 250/100 = 2.4

A very small added benefit for the producer will be that the protein added representing 3.84kg lean meat will be cheaper than the actual meat.  There is, therefore, no financial downside for the producer.  The producer is limited in how much of the protein can be added since it will start to affect the appearance and colour of the bacon.  My suspicion is that in countries like Australia, more can be added due to the fact that the bacon is sold fully cooked which yields a paler bacon as opposed to South African producers where the bacon is sold par-cooked and have a much brighter reddish-pinkish appearance.  Adding protein, I suspect,  will, therefore, have less of an impact in Australia compared to South Africa.  I will not be surprised if some Australian producers add a lot more non-meat and meat protein alike and therefore inject more brine.

The reality is that actual food legislation in Australia and New Zealand allows for a slightly different approach which we will look at in detail in the next article. For now, it is enough that we start interacting with some of the values we encounter as we learn how they were discovered.

We continue our fascinating journey by looking at the contribution of a formidable man, Justus von Liebig during whose time, protein was identified and named.  We also encounter our first ratio when Mulder estimated that meat proteins contain 16% nitrogen (N).  By multiplying the nitrogen content with 100/16, the protein content is
estimated. Therefore, nitrogen x 6.25 is the protein content.


Further Reading

Counting Nitrogen Atoms – The History of Determining Total Meat Content


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(c) eben van tonder

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Notes

(1) Nitrate is the essential curing agent and in Salpeter is coupled with potassium or sodium or calcium.

References

Bier, D. M.; The Energy Costs of Protein Metabolism: Lean and Mean on Uncle Sam’s Team, Protein and Amino Acids, 1999, Pp. 109-119. Washington, D.C., National Academy Press

Bulletin des Sciences Physiques et Naturelles en Néerlande (1838). pg 104. SUR LA COMPOSITION DE QUELQUES SUBSTANCES ANIMALES.

Carpenter, K. J.; A Short History of Nutritional Science: Part 1 (1785–1885), The Journal of Nutrition, Volume 133, Issue 3, 1 March 2003, Pages 638–645, https://doi.org/10.1093/jn/133.3.638

Hartley, Harold (1951). “Origin of the Word ‘Protein. Nature 168(4267): 244–244. Bibcode 1951Natur.168..244Hdoi10.1038/168244a0.

Munro, H. N., and Allison, J. B..  1964.  Mammalian Protein Metabolism.   Academic Press.

Vickery, H, B; The origin of the word protein” Yale journal of biology and medicine vol. 22,5 (1950): 387-93.

“Ueber die Zusammensetzung einiger thierischen Substanzen”. Journal für Praktische Chemie (in German).16: 129–152. 1839.doi10.1002/prac.18390160137

Featured Image: Venison Sausage Catalan Style, Robert Goodrick.

Chapter 08.07 Lauren Learns the Nitrogen Cycle

Bacon & the Art of Living 1

Introduction to Bacon & the Art of Living

The quest to understand how great bacon is made takes me around the world and through epic adventures. I tell the story by changing the setting from the 2000s to the late 1800s when much of the technology behind bacon curing was unraveled. I weave into the mix beautiful stories of Cape Town and use mostly my family as the other characters besides me and Oscar and Uncle Jeppe from Denmark, a good friend and someone to whom I owe much gratitude! A man who knows bacon! Most other characters have a real basis in history and I describe actual events and personal experiences set in a different historical context.

The cast I use to mould the story into is letters I wrote home during my travels.


Lauren Learns the Nitrogen Cycle

Copenhagen, August 1891

Dear Lauren,

A father’s relationship with his daughter is very special. It’s magical! This is your turn to get a letter, my precious La.  How I miss you guys!  This week I learned an important lesson, that life is about much more than science, technology, and business.

Jacobus Arnoldus Combrinck, kindsman of the Graaf brothers and founder of the Cape Town butchery that became the Imperial Cold Storage & Supply Company Ltd.

Tribute to Jacobus Combrinck

I got a telegraph on Thursday, 6 August 1891 from David de Villiers Graaff.  He told me the devastating news about the death of Uncle Cornelius Combrinck. (1)  I am immensely saddened.  He was a part of our lives for so long.  I practically grew up in his home.  He and your grandfather were friends since before I was born. I can almost not imagine going forward without him.  The knowledge of his passing left a gap in my heart.  When I read David’s message, I took a long walk and cried much.

In my mind, I see him with the two of you on his lap when you were still very small. When we visited him in his Woodstock home (2) he would put you on his knee and you would “ride horsie”.  I don’t know if you will remember this.  You were so small!

You loved going there and he loved having us over.  The large apricot trees in his back garden!  You and Tristan enjoyed climbing them.  He had the biggest garden and tended it with care. I will never forget the last time I saw him just before I left for Denmark.  He spoke to me privately and urgently.  He told me that he thinks I am finally making a good career choice.  He did not like the fact that I rode transport to Johannesburg because he believed that the railroads would soon have put me out of business.  The meat industry, he to him, is one of the iconic, almost eternal industries.  People would always need food. He told me that the chance to become proficient in one aspect of it is something I can build a future on.  Now he is gone.  Life is short.

Uncle Cornelius never had his own children, but he invested liberally in the lives of others, particularly children.  He spared no effort to mentor me, even in times when I made choices that he did not agree with.  He took the Graaff brothers into his house and cared for them as if his own.

I understand that he was buried from the Groote Kerk, in Cape Town and laid to rest in the Maitland Cemetary.  His life is an example to all of us, little La!  He was your age when he started to work in the butchery of Johannes Mechau.  His dad had passed away and his mother was desperate for extra income.  The fact that as a 10-year-old boy he had to earn his living could have been a sign that he was destined for a life of mediocrity and poverty.  The opposite was true!  By his own resolve and willpower.  Mechau found that he learned the trade quickly.

He was ambitious and left Mechau’s employment to join the leading pork butcher in town, the Swiss Ithmar Schietlin. When Schietlin returned to Switzerland, Combrinck went into business for himself.

He was very successful.  He speculated in the diamond industry in Kimberly.  He owned houses in Sea Point, Three Anchor Bay, and Wynberg.  He had sheep farms that supplied his own and other butcheries throughout the Colony.

Uncle Jakobus knew the value of a young apprentice from his own experience. He thought it best to select such an apprentice from his own people and in 1870 he visited the farm Wolfhuiskloof in the lovely Franschhoek mountains.  Like his own family situation, years earlier, the Graaff family fell on hard times and found it difficult to feed their children.  One of the children of Petrus and Anna Graaff impressed Jacobus.  The child was lively and intelligent and he suggested that David return to Cape Town with him where he would be taught the butchery trade.  The suggestion pleased everybody.  This is how it came about that David joined the butchery, Combrinck & Co. (Simons, 2000)

I am sorry that I missed his funeral but I managed to send a telex to the Graaff brothers.  It is a comfort to know that you, Tristan, and my parents attended. I wonder how Cecil Rhodes took the news of his passing? (3) (Simons, 2000)

The Best I Can Be

Lauren, I am here to learn the butcher’s trade and the art of curing bacon.  One of the best responses possible to honour the memory of Uncle Jacobus is to become the best I can be at these.

As a child on Stillehoogte, I learned that saltpeter is the magical salt that cures meat.  A friend of Uncle Jeppe, Dr. Eduard Polenski, discovered that nitrites form in bacon brine and suspects that it is the actual compound that changes pork into bacon and not saltpeter (potassium or sodium nitrate).  At the factory, I would walk behind Unkle Jeppe on the way to the curing room and he would ask me, “Eben, what changes pork into bacon?”  My answer always had to be, “Nitrite!” (4)  He would follow this up by asking, “Where does nitrite come from?” upon which I reply, “From the saltpeter, when bacteria change the nitrate into nitrite when it removes the one oxygen atom from the saltpeter molecule.”

To fully comprehend the different nitrogen compounds that play a rile in meat curing, there is another compound you must know besides nitrite (NO₂⁻) and nitrate (NO3-), namely ammonia.  In my last letter to you and Tristan, I already introduced you very briefly to it when I told you about ammonium chloride which was another great salt from antiquity that cured meat.

The three cousins of the chemical gas, nitrogen are ammonia, nitrite, and nitrates.  These three cousins are key to all life and exist almost everywhere.  It occurs naturally in sea salt, in the ground, in salt beds.  They are pervasive.  Without them, we won’t be able to shoot a gun, fertilize our fields or cure bacon.  Some people refer to it as the nitrogen cycle – the fact that nitrogen exists in the atmosphere as a stable gas, that the tight bonds are broken through the action of lightning which then frees the two nitrogen atoms so that one can react with oxygen to form nitric oxide (NO).  As it cools down, it reacts further with the oxygen molecules around it to form nitrogen dioxide (NO2) which is one nitrogen atom and two oxygen atoms.  Nitrogen Dioxide (NO2) reacts with more oxygen and raindrops.  Water is H2O.  The two oxygen atoms of nitrogen dioxide combine with the one from water to form 3 oxygen atoms bound together.  There is still only one nitrogen atom giving us NO3 or nitrate.  There is now still one Hydrogen atom left and it combines with the nitrate to form nitric acid (HNO3).  Nitric acid falls to earth and enters the soil and serves as nutrients for plants.

There is now an interaction where oxygen is added to nitrogen-containing compounds (oxidation) and removed (reduction).  Bacteria change decomposing animal and plant matter from ammonia into nitrite and nitrates and eventually back into nitrogen gas which is released into the atmosphere.  Certain bacteria change atmospheric nitrogen directly into a form that can be digested by plants.  Uncle Jeppe organized a visit for Minette and me to the University of Copenhagen where a professor in biology and chemistry took an entire morning to describe to me the most recent discoveries in this field.

I wrote to Tristan about nitrate.  I told him about saltpeter and nitrite, when I reported on the work of Dr. Eduard Polenski and his insight and experiment showing that in bacon cures, nitrate is converted to nitrite.  It has recently been shown that there is a conversion of each of these compounds into the other through the action of small organisms, called bacteria in soil and water.  It was these discoveries that gave Dr. Polenski the insight that it may be bacteria in brine, changing the nitrate ( NO3-) to nitrite (NO₂⁻).  Our visit to the University was breathtaking.  I was glad that Minette accompanied me.  I needed someone there to simply help me take notes and to remember every bit of insight shared by the Professors.  It is thrilling to share my journey of discovery with all of you!

Discovery of the Microscopic

One of the pillars of understanding nitrogen is its chemical make up.  Another is to understand bacteria and their role in these processes.  Some of the reactions in meat are driven by chemistry and some by bacteria.  Like many of our greatest discoveries, the ancients had a very good idea that the microscopic world must exist.

Bacteria and micro-organisms were discovered between 1665 and roughly 1678. Two of the men responsible for their discovery were Robert Hooke and Antoni van Leeuwenhoek. (Gest, H. 2004)  As one can imagine, the microscopic was discovered when the instruments were invented to see very small organisms.  It came about after the discovery of the microscope. The first illustrated book on microscopy was Micrographia,  published by Robert Hooke in 1665. (Gest, H. 2004)

On 23 April 1663, Hooke reported on two microscopic observations to the Royal Society, one of leaches in vinegar and another of mould on sheepskin. So opened up to humankind the magical world of the minute! The microscopic!

It was the astonishing Antoni van Leeuwenhoek from Holland who introduced us to many micro realities of our world. Here is an interesting list of some of the discoveries of this remarkable man:

In 1674, in a single vial of pond scum that he took from the Berkelse Mere, a small lake near Delft, he discovered and described the beautiful alga Spirogyra, and various ciliated and flagellated protozoa.  He found in 1674 that yeast consists of individual plant-like organisms. In 1675 he discovered and accurately described and differentiated red blood cells in humans, swine, fish, and birds. In 1677 he was the first to observe sperm cells in humans, dogs, swine, mollusks, amphibians, fish and birds. In 1679 and 1684 he described the needle-shaped microscopic crystals of sodium urate that form in the tissues of gout patients in stone-like deposits called “tophi”. In 1684, he correctly guessed that much of the pain of gout is caused by these sharp crystals poking into adjacent tissues. More than a century would pass before any further advance in the understanding of gout. He found and described in 1680 foraminifera (single-celled protists with shells) in the white cliffs of England’s Gravesend and nematodes in pond water.

Between 1680 and 1701 he carried out many microdissections, mainly on insects, making an enormous number of discoveries: He wrote extensive accounts of the mouthparts and stings of bees. He was the first to realize that “fleas have fleas”. His keen perception enabled him to correctly conclude that each of the hundreds of facets of a fly’s compound eye is, in fact, a separate eye with its own lens. This outlandish (but true) idea was met with derision by visiting scholars. The big breakthrough came in 1683. In his most celebrated attainment, he discovered the bacteria in dental tartar, including a motile bacillus, selenomonads, and amicrococcus.

16 October 1674, Antoni wrote a letter describing his study of the tongue of an ox and his observations of the taste buds. On 24 April 1676 Antoni studied pepper water that has been sitting for three weeks under his microscope. He observed small organisms that he called “little eels” (animalcules). What he was looking at were bacteria. He has discovered a world that we knew very little about!

Antoni was responsible, not just for discovering bacteria, but for discovering important classes of bacteria. He was among others responsible for identifying anaerobic bacteria. (5) (6) In a letter dated 14 June 1680 to the Royal Society, he described his discovery. This would become very important in considering the action of bacteria in meat systems since the environment is often devoid of oxygen.

The important point about bacteria that I want you to focus on is that it plays and pivotal role in the nitrogen cycle as described by Louis Pasteur. It continues the very same interaction with family members of nitrogen in the curing of meat. (Dikeman, M, Devine, C: 436) (6) (7)

Scientists in the late 1800s started to hone in on the particular bacteria responsible for converting nitrate to nitrite. This is becoming very important to us because generally, nitrate exists because of the action of bacteria, but particularly, as Dr. Eduard Polenski speculated in 1891, it is the action of bacteria that turns nitrate from saltpeter into nitrite in curing brines and meat that is being cured. The question we have been asking is if this was a fair assumption for him to make and the answer is an overwhelming “yes!”

From 1868 it has been known that bacteria in soil are responsible for the exact same reduction.  It was known for 23 years before Dr. Polenski’s 1891 experiments on curing brine and the meat being cured. The reduction of nitrate in soil to nitrite or ammonia was brought about by various forms of microorganisms. The person who demonstrated this in 1868 was the German scientist C F Schonbein. Our French friends, Gayon and Dupetit, confirmed this. (Waksman, SA, 1927 : 181)

Adding carbohydrates, glycerol, and organic acids, in addition to peptone (a soluble protein formed in the early stage of protein breakdown during digestion) to meat through its brine stimulate the reduction of nitrate to nitrite.  It was also discovered that an abundance of oxygen hindered it. (Waksman, SA, 1927 : 181)  This will prove to be of the greatest importance to meat curing and since we can achieve a brighter colour by adding organic acids, glycerol, carbohydrates and reducing sugars to the brine mix.

One researcher, Maassen, tested 109 different bacteria and found that 85 were capable of reducing nitrate to nitrite, especially Bact. Pyocyaneum. Similar results were found by others who studied this.  Not only did they find that many of the bacteria responsible for the reduction were anaerobic (functioning in the absence of oxygen) but that many strict aerobic bacteria were found to act anaerobically in the presence of nitrates. (Waksman, SA, 1927 : 181)  This was true of soil and certainly, it should be true in meat and brine systems also!

Ammonium Chloride (Sal Ammoniac)

We have seen that nitrite is formed by removing an oxygen atom from nitrogen.  There is another very important way that nitrate is formed namely when ammonia breaks down.   The Russian microbiologist Sergei Winogradsky discovered this.  Microorganisms, through a process called biological oxidation, change ammonia to nitrite and nitrite to nitrate.  Have a look at how oxygen is added at every step. Ammonia is NH3  and there is no oxygen.  Nitrite is formed NOwhich is the nitrogen and two oxygen atoms.  From nitrite, through bacterial action, nitrate is formed NO3.  So, from a form with no oxygen, the most oxygenated state is reached namely nitrate with its three oxygen atoms.

We have to understand a bit more about ammonia to see how this works.  This will be very important when we look at the decomposition of animal tissue and in animal urine and excrement since it contains copious amounts of ammonia.  The building blocks of ammonia is seen in its chemical formulation. Ammonia is a compound of nitrogen and hydrogen with the formula NH3.

In nature, ammonia exists as NH3 or its ammonium ion (NH4+). The ammonium ion, in nature, also combines with a metal such as chlorine to form a salt of ammonium.  Ammonium is therefore not only important in the nitrogen cycle, but also in meat curing in the form of a salt where a metal such as chloride combined with the ammonium ion to form ammonium chloride (NH4Cl).  It is the NHwhich makes it mildly acidic and the new molecule of sal ammoniac or ammonium chloride is highly reactive with water.  Ammonium chloride occurs naturally as a crystal and it is formed through the action of bacteria on decomposing organic material. As a salt, it is one of the iconic salts of antiquity.

Natural Sal Ammoniac

Ammonium chloride occurs naturally in the smoking mountains of Turfan and in Samarkand where volcanic fumes are released through vents. The crystals form directly from the gaseous state, skipping the liquid state.  The crystal that is formed tends to be short-lived, as they dissolve easily in water.  This is the basis for my guess that in Turfan, where ammonium chloride occurs in the mountains and nitrate in the depression but they have a similar effect on meat.  Once the crystalline form of ammonium chloride comes into contact with moisture it breaks down to a brownish salt which looks similar to the nitrate salts found on the top layer of soil in the depression between the mountains.  I suspect that these nitrate salts were sold as “fake” ammonium chloride because it has overlapping characteristics because of the nitrogen.

Turpan to Samarkand.png

Natural Sal Ammoniac occurs in places like the Turpan and Samarkand.  An important branch of the silk road runs from Turfan runs through Samarkand and into Europe.  Samarkand is a city in south-eastern Uzbekistan.  It is one of the oldest continuously inhabited cities in Central Asia.

In China, ancient names given for Sal Ammoniac are “red gravel” and “essence of the white sea.”  There were sal ammoniac mines in Soghd. Mohammadan traders passed it at Khorasan traveling towards China.  Kuča still yielded sal ammoniac at the beginning of the 1900s. There are ancient references to white and red varieties of sal ammoniac.  The mines in Setrušteh or سمرقند‎ (Samarkand in the Persian language) are described in classic literature as follows.  “The mines of sal ammoniac are in the mountains, where there is a certain cavern, fro wich a vapour issues, appearing by day like smoke, and by night like fire.  Over the spot whence the vapour issues, they have erected a house the doors and windows of which and plastered over by clay that none of the vapour can escape. On the upper part of this house the copperas rest.  When the doors are to be opened, a swiftly-running man is chosen, who, having his body covered over with clay, opens the door; takes as much as he can from the copperas and runs off; if he should delay he should be burnt.  This vapour comes forth in different places, from time to time; when it ceases to issue from one place, they dig in another until it appears, and then they erect that kind of house over it; if they did not erect this house, the vapour would burn, or evaporate away.”  (Laufer,1919)

Tibetans received this salt from India as can be seen from an ancient name they gave to it namely “Indian salt.”  There are records that it was harvested from certain volcanic springs from Tibet and Se-č’wan.  (Laufer,1919)  The same vapours are seen in the smokey mountains of Turfan.

Human-Made Ammonium Chloride

Just like saltpeter, sal ammoniac occurs naturally and is also generated through human endeavour.  The name, ammonia, came from the ancient Egyptian god,  Amun.  The Greek form of Amun is Ammon.  At the temple dedicated to Ammon and Zeus near the Siva Oasis in Lybia, priests and travelers would burn soil rich in ammonium chloride. The ammonium chloride is formed from the soil, being drenched with nitrogen waste from animal dung and urine.  The ammonia salts were called sal ammoniac or “salt of ammonia” by the Romans because the salt deposits were found in the area.  During the middle ages, ammonia was made through human endeavour through the distilling of animal dung, hooves, and horns.   (Myers, RL.  2007:  27)

The New-York Tribune of 31 January 1874 wrote the following.  “For centuries sal ammoniac was imported from Egypt where it is sublimed from camels dung.” An article, published in 1786 on Friday, 18 August in the Pennsylvania Packet, described the process of making sal ammoniac in Egypt as follows.  “Sal Ammoniac is made from soot arising from the burnet dung of four-footed animals that feed only on vegetables.  But the dung of these animals is fit to burn for sal ammoniac only during the four firsts months of the year when they feed on fresh spring grass, which, in Egypt is a kind of trefoil or clover; for when they feed only on dry meat, it will not do.  The dung of oxen, buffalos, sheep, goats, horses, and asses, are at the proper time as fit as the dung of camels for this purpose; it is said that even human dung is equal to any other.”

“The soot arising from the burnt dung is put into glass, vessels, and these vessels into an oven or kiln which is heated by degrees and at last urged with a very strong fire for three successive nights and days, the smoke first shews itself, and, in a short time after, the salt appears sticking to the glasses, and, by degrees, covers the whole opening.  The glasses are then broken, and the salt taken out in the same state and form in which it is sent to Europe.”  At this time, Egypt was one of the major suppliers of sal ammoniac to the European continent.

Discovery of gasses

– Joseph Black

At this point in the development of chemical technology, a much bigger development took place in which the discovery of nitrogen and ammonia is only a small part of.   In the 1770s scientists started to realise that the atmosphere is made up of various gasses.  This was the start of the chemical revolution and the discovery of gasses was, in a way, the major propellant.  Up to this time gasses were not regarded as a separate chemical entity and largely ignored in experimental work.  The drawback was major and real advances became only possible as this was being resolved.  One of its pioneers was Joseph Black (1728–1799).  Black is credited with the discovery of carbon dioxide (fixed air).

– Charl Wilhelm Scheele

The Swedish Chemist, Charl Wilhelm Scheele (1742 – 1786) prepared oxygen by heating saltpeter (potassium nitrate, KNO3) in 1770.  Somewhere between 1771 and 1772, he became the first scientist to realise that “air consists of two fluids different from each other, the one that does not manifest in the least the property of attracting phlogiston while the other … is peculiarly disposed to such attraction.” (Smil, 2001: 2)   Phlogiston was believed to be the substance present in all material that burns, responsible for combustion. The one substance is obviously oxygen and the other nitrogen.

– Daniel Rutherford

At the same time, Daniel Rutherford (1749–1819), a pupil of Black, obtained his doctorate in Medicine in 1772 from the University of Edinburgh.  In his “Dissertatio inauguralis de Aere Fixo Dicto, aut Mephitico” (Rutherford, 1772) he records the following experiment.  He placed mice in a closed-in environment.  Eventually, the mice will die and Rutherford expected to find was that the only air that is left will not be able to support life and a flame will not burn in it.  He removed the fixed or mephitic air (carbon dioxide) with a caustic potash solution (alkali).  He found a residual gas still incapable of supporting respiration or fire, similar to carbon dioxide, but unlike carbon dioxide, did not precipitate lime water and was not absorbed by the alkali.  He thus discovered a residue of his fixed or mephitic air.  He named it “aer malignus” or noxious air.”  (Munro and Allison, 1964)

– Joseph Priestley

Priestly, who is credited for the discovery of oxygen (1774 – 1775) presented experimental evidence similar to Rutherford’s before the Royal Society of London.  He, however, did not draw conclusions regarding the possible nature of the gas (Priestley, 1772).

– Isolation of Ammonia

The identification of nitrogen was “in the air”, so to speak and as we will see, never far removed from meat curing.  Sal Ammoniac (ammonium chloride, NH4Cl) was used since antiquity as a curing and preserving agent of meat and was investigated by none other than Joseph Black.  In 1756 he became the first to isolate gaseous ammonia by reacting sal ammoniac with calcined magnesia (Magnesium Oxide). (Black, 1893) (Maurice P. Crosland, 2004).  Scientists were now widely experimenting with gasses and along with air, gasses like ammonia received a great deal of attention.  It would later be discovered that nitrogen is its key constituent in ammonia along with hydrogen.

Following Black, ammonia was, for example, also isolated again by Peter Woulfe in 1767 (Woulfe), by Carl Wilhelm Scheele in 1770 (kb.osu.edu) and by Joseph Priestley in 1773 and was termed by him “alkaline air”. Eleven years later in 1785, Claude Louis Berthollet finally unraveled its composition. (Chisholm, 1911) (Berthollet, 1785)

Priestley, in Part II of his work, Experiments and Observations,  described work from between the years 1773 and the beginning of 1774.  In this document, he gives a reprint of an earlier publication on effluvia from putrid marshes.  Here he identifies ammonia and nitrous oxide.  (Schofield, RE.  2004:  98)

His discoveries on ammonia were the result of a consistent application of the English scientist, Stephen Hales’s (1677 – 1761) technique for distilling and fermenting every substance he could get his hands on or capture over mercury rather than over customary water so that the air would “release.”  He heated ammonia water and collected a vapour.  When it cooled down, it did not condense, proving it was air.  He called it alkaline air.  (Schofield, RE.  2004: 98, 103, 104)

More experiments showed him that alkaline air was heavier than common inflammable air but lighter than acid air.   It dissolved easily in water, producing heat and it was slightly inflammable in the sense that a candle burned in it with an enlarged colour flame before going out.  In the end, he not only described ammonia chemically, but also its mode of production, and its characteristics.   (Schofield, RE.  2004: 98, 103, 104)

– From Ammonia to Nitrogen

In 1781 the French Chemist, Claude Louis Bertholett became aware that something joined with hydrogen to form ammonia (NH3).  Three years later, Claude joined Lavoisier who was responsible for unraveling the composition of saltpeter along with de Morveau and de Fourcroy, in naming the substance azote.  (Smil, V.  2001:  61, 62)  Lavoisier named it from ancient Greek, ἀ- (without) and zoe (life).  He saw it as part of air that can not sustain life.  In 1790 Jean Antoine Claude Chaptal, in a French text on chemistry which was translated into English in 1791, gave it the name “nitrogen”.  He used the name ‘nitrogène’ and the idea behind the name was “the characteristic and exclusive property of this gas, which forms the radical of the nitric acid,” and thus be chemically more specific than “azote.””  (Munro and Allison, 1964)  As for ammonia, its modern name was given in 1782 by the Swedish chemist Torbern Bergman.  (Myers, RL.  2007:  27)  The discovery of hydrogen, the other component in ammonia, is credited to Cavendish in 1766.

A Hint of Nitrogen in Animals

The relation between nitrogen through ammonia and animal bodies was known from early on.  In 1785, Claude Berthollet reported to the French Academy of Sciences that he found that the vapor that came from decomposing animal matter was ammonia.  When he realised the gas, he found that it was composed of three volumes of hydrogen and one volume of nitrogen, or around 17% hydrogen and 83% nitrogen by weight.  He was very accurate in his measurements and the modern values of these are given as 17.75% and 82.25% respectively.  (Carpenter, 2003)

Techniques for Testing for Nitrogen

Key to the identification of nitrogen in animal substances was developing the tools to test for it.   One of the earliest tests was the oxidation of organic material in the presence of cupric oxide.  The gasses resulting from this reaction is then collected and measured.  It was extensively developed by none other than Gay-Lussac while he was professor at the Sorbonne, and later when he was a chemist at the Jardin des Plantes in Paris.  (Sahyun, M. (Editor). 1948)

The method of Gay-Lussac was modified by Jean Dumas (1800-1884) and used by Dumas’ contemporary, Liebig. Despite the many alterations of the basic method of micro procedures, the Dumas method would continue to be the preferred one well into the 1900s.  In 1841, F. Varrentrapp and H. Will developed a total nitrogen method.  This method is based on the liberation of ammonia by heating protein with alkali, followed by gravimetric estimation of the ammonia as its chloroplatinate.  (Sahyun, M. (Editor). 1948)

A downside to this method was the fact that it is slow and tedious with fundamental inaccuracies.  It had, however, specific technical advantages over that of the Dumas-method when applied to metabolic observations and it was used in many early studies.  The famous method we are all familiar with today is the Kjeldahl method.   It was developed by the Danish chemist, J. Kjeldahl (1849-1900), of Carlsberg, who in 1883 presented a much-improved method for catalyzed digestion of nitrogenous materials in sulfuric acid which allowed for the production of ammonia quantitatively.  (Sahyun, M. (Editor). 1948)

Nitrogen in Respiration

Antoine Lavoisier was inspired by Joseph Black, something that Lavoisier was not shy to admit.  He wrote Balck a letter, dated 19 November 1790, where he describes experiments on the respiration of human subjects.  He showed that oxygen is consumed and carbon dioxide evolved during this process.  Interestingly he showed that oxygen consumption increases by some 50% above the basal level after a meal (the modern specific dynamic action of food) and that in severe exercise, oxygen consumption can increase by as much as three-and-a-half times.  The measurements were accurate, even by modern standards.   Part of the letter states: “Legaz azote ne sert absolument à rien dans l’acte de la res piration et il ressort du poumon en même quantité et qualité qu’il y est entré” which translates to Nitrogen is absolutely useless in the act of respiration, and it appears from the lung in the same quantity and quality that it has entered it.

They had their test subjects exercise in a closed container.  They measured for oxygen and carbon dioxide.  They also measured the amount of nitrogen ingested during a meal before the experiments started and then, after exercise, the urine and stools were tested to see how much nitrogen was retained in the body or “lost” through the urine and stools.

The experiment was undertaken 18 years after the discovery of nitrogen.  It is regarded by many as the first metabolic experiment with nitrogen.  The experiments appear (D. McKie, personal communication, 1962) to have been based on studies made by Fourcroy in the late 1780s, using gasometric methods that were published in 1791 by Séguin.  They did not find any correlation between nitrogen and respiration.  Some researchers of the time still claimed that some nitrogen is lost from the body during respiration.  Today, most will simply subscribe to Lavoisier’s view that gaseous nitrogen plays no part in the nitrogen metabolism of the mammalian organism.  (Munro and Allison, 1964)  They believed that the balance of nitrogen ingested and that which was not recovered in stools or urine was probably lost through what they called “insensible perspiration.”  (Carpenter, 2003)

Antoine Lavoisier and Armand Seguin’s experiment of human respiration showed that breathing had no influence on nitrogen levels.  It had other positive results.  An increase in the output of carbon dioxide (carbonic acid, as they called it) during exercise was demonstrated.  They measured this at rest and while lifting weights.  This was by itself a step forward.  At the time it was believed that the only purpose of respiration was to cool the heart.   (Carpenter, 2003)

Lavoisier, in collaboration with a mathematician and one of the greatest scientists of the time, Pierre-Simon Laplace, identified the slow combustion of organic compounds in animal tissue as the major source of body heat.  In their experiments, they compared the heat produced by the guinea pig and the production of carbon dioxide with the heat produced by a lighted candle or charcoal. They used an ice calorimeter to measure heat production.  The instrument itself is very interesting.  It measures the heat generated by relating it to the weight of water released from the melting of the ice surrounding the inner chamber where the animal or burning material is housed.  The measurements are crude and not very precise, but results were consistent and it allowed the researchers to draw the conclusion of the origin of body heat.  (Carpenter, 2003)

Momentous political movements in France of the time would put an end to one of the most brilliant scientific careers of any person to have lived on earth.  Lavoisier returned to further studies on respiration and was arrested in 1793 during the Reign of Terror and kept in prison.  He pleased with the for a short stay of execution on the day of his trial in 1794, to be allowed one more experiment, but the judge is believed to have replied that the Republic had no need of “savants” (scientists), and he was guillotined the same afternoon. (Carpenter, 2003)

Nitrogen in Animal Matter

Lavoisier introduced order into the study of the new chemistry. One of his great achievements was the vigorous school of chemists he left behind.  Some of his students took up the work on organic compounds and applied procedures in which gas was either evolved or removed. Gay-Lussac (a pupil of Lavoisier’s collaborator, Berthollet) and Thénard worked out a system of organic analysis in 1810.  Accordingly,  the organic material is treated with potassium chlorate and the amount of oxygen and nitrogen liberated is measured (Partington, 1951). The Dumas procedure, which we eluded to above, remained the standard gasometric method of nitrogen analysis.  It was developed in 1830. (Partington, 1951). The studies made by Magendie on the importance of nitrogenous components in the diet was one of the matters to be elucidated by the new technique. (Munro and Allison, 1964) Viewed in this way, the persona and influence of Lavoisier continued to directly affect the work he started long after his untimely death.

It was confirmed that animal matter contains nitrogen and it was shown to be absent from sugars, starch, and fats.  It was long suspected that wheat flour contained matter with characteristics closely associated with animal matter.  This was proved, that gluten (the plant matter) has properties of animal matter, including the development of alkaline vapor when it was allowed to rot.  When potatoes were introduced, there was a debate if it could provide an adequate substitution for wheat because it did not have anything resembling gluten.  Was it the gluten that made wheat flour good food?  (Munro and Allison, 1964)

Bartolomeo Baccari (1682 – 1766) was a professor at the University of Bologna for most of his life.  In 1734, one of his papers entitled “de Frumento,” appeared.  In this paper, he gives details on how to prepare gluten which was found and later it was found to be the protein portion of wheat flour.  The following is translated from Latin:

“This is a thing of little labor. Flour is taken of the best wheat, ground moderately lest the bran goes through the sieve, for it ought to be purified as far as possible in order that all suspicion of mixture should be removed.  Then it is mixed with the purest water and agitated. What remains after this process is set free by washing, for water carries off with itself whatever it is able to dissolve. The rest remains untouched.”

“Afterward that which the water leaves is taken in the hands and pressed together and is gradually converted into a soft mass and beyond what I could have believed tenacious, a remarkable kind of glue and suitable for many purposes, among which it is worth mentioning that it can no longer be mixed with water. Those other parts which the water carries away with itself for some time float and render the water milky. Afterward, they gradually settle to the bottom but do not adhere together; but like a powder return upward at the slightest agitation. Nothing is more nearly related to this than starch or better, it is indeed starch.”

He classified the starchy material as flour.  He described the following characteristics.  It ferments to give acid spirits, indicating its “vegetable nature.” On the other hand, it had a characteristic of “animal nature” for “within a few days it gets sour and rots and very stinkingly putrifies like a dead body.”

This was an old way to distinguishing what we call today proteins from carbohydrates. There was a theory at this time that vegetable protein which is consumed by herbivores changes into the flesh and blood of the animal.  This was still prevalent during the time of Mulder and Liebig’s. (Sahyun, M. (Editor). 1948)  Another question was the source of the nitrogen in animal bodies.  Since nitrogen is most prevalent in the air around us, some chemists suggested that animals get the nitrogen from the air through a kind of combination must occur during an animal’s digestion of plant foods “so as to give the ingesta the characteristics that would allow them to be incorporated into the animal’s own tissues either for growth or replacement of worn-out materials.”  (Carpenter, 2003)  The mechanisms of nutrition were in a developmental process.

François Magendie: Nitrogen as the basis for Nutrition

A major step came from the work of Magendie (1783–1855) who linked the nitrogen of inanimate substances with that of living systems.  He was the first to recognise that there is a major difference between the nutritional value of food containing nitrogen and those without it.  Magendie grew up in revolutionary Paris and practiced as a surgeon before changing to physiology.

In his first work on the subject, reported to the Academy of Sciences in 1816, Magendie addressed the question of whether animals could access atmospheric nitrogen to “animalize” ingested foods of low nitrogen content.  (Carpenter, 2003)

In his 1816 article, “Sur les propriétés nutritives des substances qui ne contiennent pas d’azote.” (On the nutritional properties of substances that do not contain nitrogen),  Magendie famously described experiments on dogs that were only fed carbohydrate (sugar) or fat (olive oil) until they all died in a few week’s time. The conclusion is obvious that a nitrogen source was an essential component of the diet.

As we look back at these early experiments we can see that the results were complicated by vitamin deficiencies, yet they were the first approximations to an ideal—the long-term feeding experiment with purified foodstuffs—which has only been attained in recent years. They can rightfully be seen as forerunners of the classical procedure for establishing whether a nutrient is essential to the body, namely by excluding it from the diet and then looking for symptoms attributable to its deficiency.

In his “Elementary Compendium of Physiology for the Use of Students,” Magendie draws and even clearer distinction between nitrogenous and nonnitrogenous foods. The first edition appeared in 1817 and the third edition was translated into English in 1829. Magendie’s compendium of work is very different from earlier writers like Haller’s “Elementa Physiologiae,” (1757–65).  Magendie did not write in Latin and he clearly departed from the primeval forests of mystery and speculation.  His work is done with the illumination of bright sunshine of scientific observation and deductive reasoning.

Again, we have to give credit to the monumental work of Lavoisier.  Magendie’s success in the physiology of nutrition directly stems from the influence of Lavoisier’s vigorous school of chemistry, which had grown up in the interval.  Megandie followed his 1816 work where he fed dogs only carbohydrates or fat with new experiments. In these, he fed them exclusively on cheese or eggs, both nitrogenous foods.  The dogs survived indefinitely, although they were weak. Magendie concluded that “these facts . . . make it very probable that the azote of the organs is produced by the food.”

Magendie’s inquiring mind also extended to views on how the diet was utilized by the tissues of the body. In his textbook (p. 18), he says: … The life of man and that of other organised bodies are founded upon this, that they habitually assimilate to themselves a certain quantity of matter, which we name aliment. The privation of that matter, during even a very limited period, brings with it necessarily the cessation of life. On the other side, daily observation teaches, that the organs of man, as well as those of all living beings, lose, at each instant, a certain quantity of that matter which composes them; nay, it is on the necessity of repairing these habitual losses that the want of aliment is founded. From these two data, and from others which we shall make known afterward, we justly conclude, that living bodies are by no means always composed of the same matter at every period of their existence. . . . It is extremely probable that all parts of the body of man experience an intestine movement, which has the double effect of expelling the molecules that can or ought no longer to compose the organs, and replacing them by new molecules. This internal, intimate motion, constitutes nutrition. And again (p. 468), … Nutrition is more or less rapid according to the tissues. The glands, the muscles, skin, etc. change their volume, colour, consistence, with great quickness; the tendons, fibrous membranes, the bones, the cartilages, appear to have a much slower nutrition, for their physical properties change but slowly by the effect of age and disease.” (Munro and Allison, 1964) (14)

When one looks back at history, one tries to bridge the linguistic and cultural divide.  An important assumption underpinning Magendie’s work is that an animal species could be used as a model for humans; that our bodies are essentially of the same general character.  A possible reason for this is the interest that existed in France for studies in comparative anatomy.   (Carpenter, 2003)

Jean Baptiste Boussingault

Another active investigator in France in the 1830s, with a quite different background from that of Magendie, was also studying the source of an animal’s nitrogen-rich tissues. This was Jean Baptiste Boussingault, the great “farmer of Bechelbrom,” who had learned his chemistry in a school for mining engineers. After a period of adventurous geological exploration in South America, he returned, married a farm owner’s daughter and put his mind to agricultural science. He obtained a position at the Sorbonne in Paris, where he collaborated with J. B. Dumas, one of the leading French chemists, and divided his year between Paris and the farm.  (Carpenter, 2003)

It was Boussingault who realised in 1836, over sixty centuries after it was noted and recorded that manure and legumes were beneficial to crop production, that it was the nitrogen content in the soil or fertiliser which is important for plant nutrition. In 1838, he performed a number of experiments where he grew legumes in sand with no nitrogen in it. The legumes continued to grow and the only conclusion he could come to was that they took their nitrogen from the air.  How they did it, he still had no idea.   (Galloway, J. N, et al., 2013)  He was able to show that this was not possible for cereal grain.

His next subjects were cows and horses, whose common feeds were believed to be exceptionally low in nitrogen. First, he wanted to determine the level of feeding that would ensure that his animals are kept at constant weight, and then for 3 days, he recorded the animal’s feed, what was excreted and, in the case of the cow, its milk.  All these were analised for its nitrogen content. The results for the horse was that he received 8.5kg hay and oats, every 24 hours.  The daily nitrogen intake was 139g, and the nitrogen recovered in urine and dung came to only 116g. When the cow was fed on hay and potatoes the figures were as follows.  The daily intake of nitrogen was 201g and the recovered output, including 46g from milk, was only 175g. This showed that the animals’ feed provided enough nitrogen to meet their needs.  There was no need to speculate about them getting their nitrogen from the atmosphere.

It is important to have some understanding of how these trails were carried out.  Many thousands of “balance” trials followed the Boussingault tests that continue to be carried out until today. A drawback was the method he used to test for nitrogen.  The system of analysis required the sample to first be dried.  There would have been a loss of ammonia when he was drying urine and dung. This probably gives the reason why there seems to have been an apparent “positive” balance in these animals that were assumed to be in a steady state.”  (Carpenter, 2003)

Nitrogen and the Nutritional Value of Plants

Boussingault had proposed that the nutritional values of plant food could be extrapolated from their contents of nitrogen.  These speculations came from before he did his balance experiments with herbivores.  His reasoning was more or less as follows.  “Magendie has shown that foods that do not contain nitrogen cannot continue to support life, therefore the nutritional value of a vegetable substance resides principally in the gluten and vegetable albumin that it contains.” Researchers of the time knew that animal bodies contained minerals which they got from the food they ate. Even earlier, two workers had written that: “Beans are so nourishing because they contain starch, an animal matter, phosphate, lime, magnesia, potash, and iron. They yield at once the aliments and the materials proper to form and color the blood and to nourish the bones”. Perhaps in response to such criticism, Boussingault explained, “I am far from regarding nitrogenous materials alone as sufficient for the nutrition of animals; but it is a fact that where nitrogenous materials are present at high levels in vegetables they are generally accompanied by the other organic and inorganic substances which are also needed for nutrition”. It is clear from the context that the “organic substances” to which he is referring are starches and not any hypothetical trace nutrients.  (Carpenter, 2003)

Synthesis by plants

Dumas, a colleague of Boussingault’s concluded in the early 1800s that the plant kingdom alone was capable of synthesizing the kinds of nitrogenous compounds abundant in animal tissues. Then, from the observation that the overall reactions of animals were characterized by oxidation, he made the further generalization that the animal kingdom was only capable of oxidizing the materials that are obtained from its plant food. (Carpenter, 2003)

Ammonia, Nitrite, and Nitrate

Ammonia is changed into nitrites or nitrated through the action of what was called a “microscopic ferment.”  The next step would be the discovery of how nitrogen changes into its cousins and enters the earth and living plants and animals.

NollLab_lg
A science class uses microscopes in a lab in 1908. (University Archives Photo)

The afternoons with Jeppe became challenging as I tried to keep up with his lectures.  He seemed to remember the names and formulations off by heart and I was not always sure who or what we were talking about.  It was nevertheless engaging and I tried to keep up.

– How does nitrogen enter the plant kingdom?

The animal kingdom gets its nitrogen from the plant kingdom.  We now return to the matter of how nitrogen enters the plant world.  When we looked at the discovery of the microscopic world, we jumped to the discovery of nitrification and the reduction of oxygen in various nitrogen compounds.  With the background information on nitrogen and its role in nutrition, let’s look at the progression of thought on ways that nitrogen enters our world.

HB de Saussure (1740 – 1799) discovered that the nitrogen in plants does not come directly from the atmosphere.  (Bynum, WF, et al, 1981:  300)  He was born in Switzerland and became interested in biology and geography.  Most of his discoveries he made while scaling some of the highest mountain peaks and passes in the world.  He regarded the Alps as central to understand the geology of the world and spend much time there.

His idea was that nitrogen must be taken up through the roots of plants, through the decomposition of humus (9, 11).    (Bynum, WF, et al, 1981:  300)  Not everybody agreed with him and a debate developed that raged for almost 50 years.  The German chemist, Justice von Liebig (1803 – 1873), was the first to see nitrogen as an essential plant nutrient.  This discovery gave him the honour of being regarded as the father of the fertilizer industry.  Justice was also an important man in the meat processing industry.  He developed the manufacturing process for beef extract and founded a company, Liebig Extract of Meat Company, and later trademarked the Oxo brand beef bouillon cube. (10)

This question of how nitrogen was absorbed by plants remained very controversial (11).  Justice believed it is taken directly from ammonia gas in the air.  (Craine, JM,  2008:  70)  This was the state of affairs until a French chemist, Boussingault (1802 – 1887) demonstrated that plants are incapable of absorbing free nitrogen but were able to flourish even without humus as long as alternative sources of nitrates or ammoniacal salts are supplied.  (Bynum, WF, et al, 1981:  300)

Boussingault and his contemporaries saw the uptake of ammonia as purely chemical. (Bynum, WF, et al, 1981:  300)  What other way could there be?  The great German physiologist, Theodor Schwann, born in 1810, took a step closer to the solution.  He discovered that alcoholic fermentation and the fermentation that causes putrefaction was carried out by microbes. (12)  (Barnett, JA)

Louis Pasteur, born in 1822 grew up to become very important in the field of science.  He was the first one to suggest that microorganisms may be involved in the nitrogen absorption process of plant.  (Bynum, WF, et al, 1981:  300)  He studied the breakdown and reorganization of material that contained nitrogen by soil bacteria, fungi, and algae.  It seemed that nitrogen was not used up but was circulated.  Decaying humus gave ammonia, from which microorganisms constructed nitric acid and its compounds.  These were then absorbed by plants and turned into proteins and incorporated into living substance.  The cycle was completed by the death and natural decay of the plant and the animal. (Bynum, WF, et al, 1981:  300)  At the death of the animal, the process of nitrification was reversed and microbes were again responsible for breaking the molecules down until only gaseous nitrogen remained.

The German agricultural chemist, Hermann Hellriegel (1831-1895), discovered that certain plants (leguminous) take atmospheric nitrogen and “replenished the ammonium in the soil through the process now known as nitrogen fixation. He found that the nodules on the roots of legumes are the location where nitrogen fixation takes place.”  (Boundless, 2014)

Hermann did not discover how this is done. Martinus Willem Beijerinck (March 16, 1851 – January 1, 1931), a Dutch microbiologist and botanist, discovered that the small growth areas on the roots contained bacteria.  He called it rhizobia.  It is the rhizobia that are responsible for changing the nitrogen to ammonium.  Ammonia is NH3 and ammonium is NH4.  (Boundless, 2014)  Soon more ways were discovered that changed nitrogen in the air into a form that plants can absorb.

Berthelot described in 1885 how lightning was responsible for nitrogen fixation before he too turned his attention to microscopic organisms in the ground that is responsible for nitrogen fixation. (Elmerich, C, Newton, WE.  2007:  3)  The energy of a lightning strike disrupts the nitrogen (N2) and oxygen (O2) molecules in the air producing highly reactive nitrogen and oxygen atoms that attract other nitrogen (N2) and oxygen (O2) molecules that form nitrogen oxides that eventually become nitrates. (Zumbal, 2000:  924)  Alternatively, Beijerinck’s rhizobia bacteria fix the atmospheric nitrogen directly (Boundless, 2014)  in small growths on plant roots such as beans, peas and alfalfa (Zumbal, 2000: 924), or animal droppings and urea or dead animal or plants provide saprobiotic bacteria, nitrogen or nitrogen-family members that can be changed.

Nitrogen is turned directly into either ammonia (NH3) or ammonium (NH4) or into nitrate (NO3).  Nitrifying bacteria turns the ammonia into nitrite.  Nitrite is toxic and nitrifying bacteria change the nitrites into nitrates that either becomes plant food along with nitrate’s that are formed during lightning strikes or are changed back into nitrogen by denitrifying bacteria.

Chemical Engineering at MIT
Chemical Engineering at MIT

A friend of Jeppe, Dr. Polenski found in 1891, months before I arrived in Denmark, that when he mixed curing brine for bacon with Saltpeter and tested it, that he found nitrate to be present.  After a week, when he tested it again, there were only nitrites. The same with the meat that he cured.  At the beginning of the week, there was nitrate present in the meat and later he found only nitrites. (13)

The notion that bacteria are responsible for changing the nitrate to nitrite was well established by the time he did the experiment and so, his conclusion that what had happened in the brine was the result of bacteria was reasonable.  It would not surprise me if it would be shown that nitrite is responsible for curing and not nitrate. (8)

I realised that saltpeter was a key part of the world we live in.  The energy of the acid in the air, harnessed by an entire world of microorganisms that probably occur in every environment on earth and changed into a format that plants and then humans and animals can absorb.    An acid, coupled with a salt, helping us to preserve meat and change pork meat into bacon, grow plants, feed oceans and drive the processes of the earth.  By it we fight wars, we grow crops and we eat and live!

food 2

At night after supper we are reading Foods by Edward Smith.  He wrote on bacon and said, “bacon is the poor man’s food, having a value to the masses which is appreciated in proportion to their poverty, and it is a duty to offer every facility for its production in the homes of the poor.” (Smith, Edward, 1876:  65) The reason why it is good for the poor is that it can be cooked in water and the liquid part can be given to the children and the solid part consumed by the parents and “thus both be in a degree pleased, if not satisfied.” (Smith, Edward, 1876:  65)

He continues to say that “it is also the rich man’s food, for the flavour, which is naturally or artificially acquired by drying (and curing), is highly prized, and although it may be taken as a necessary by the rich, it is in universal request as a luxury”  (Smith, Edward, 1876:  65)

This is our business plan.  To produce the best bacon on earth.  Uncle Cornelius passed away after a full life and I can not help to see our current quest as a necessary evolution of time as young and new thoughts replace older methods.  The evolution must in the first place be predicated on sound science as well as common sense.

This is then your chance to discover the nitrogen cycle from the perspective of a meat scientist.  I miss you, my little girl.  There is not a single day that I don’t think off you!  It’s late.  I am sure that you are fast asleep by this time and that you are holding your bear and dream of the cumming summer.

I learn so much and still, you are my biggest lesson in life.  Your love and your spirit have taught me how to live myself!

I count the days till I see you guys again!  I miss you all so much and love you!

Your Dad.


Practical Applications for the Modern Bacon Curer

In this section, I highlight some of the points of application in the modern high throughput bacon plant.

A friend of mine from the bacon industry in Castlemaine, Australia recently interacted with me on the matter of total meat content in bacon.  Nitrogen is a constituent of the meat protein and important in its nutritional value.  This identification and the subsequent determination of a phenomenally stable nitrogen percentage in meat lead to a number of important applications and implications, among others, a way to determine lean meat content and total meat content in meat processing.

A good summary of the thinking early in the late 1800s and early 1900s on the subject exists in the old South African Food, Drugs and Disinfectants Act No. 13 of 1929 (See note 1).  It has subsequently been repealed, but the basis of the law is still very much applicable. As an important historical document, it sets out the determination of total meat content.  It essentially remained unchanged (apart from minor updates).

The calculations of total meat content are defined in subparagraph 4 (iv) which reads as follows: “In all cases where it is necessary to calculate total meat under regulations 14 (1), (2), (3) and (4), the formula used shall be:—

Percentage Lean Meat = (Percentage Protein Nitrogen × 30 ).
Percentage Total Meat = (Percentage Lean Meat + Percentage Fat).

The questions of interest are how did they arrive at this and how accurate an indication is it of total meat content?  What is the relationship between nitrogen and nutrition?  When decay takes place, what happens with the nitrogen in the protein?  How does the amount of nitrogen we consume determine the total nitrogen content of our bodies or any animal or plant for that matter?  What is the value of nitrogen to the body which makes it essential for nutrition?  How does nitrogen move from a plant or an animal into our bodies to provide nutrition?  What is the impact of processing on nutrition and the total nitrogen content?  Can the standard calculation for fresh meat be applied to processed products?  Lastly and equally fascinating, what are other sources of nitrogen that can increase the total nitrogen count and skew the nitrogen count in a product and its relationship and to meat content.

This short series of articles set out to deal with these fascinating issues.  In this first article, we will look at the time from the start of the chemical revolution to Boussingault.   Sincere thanks to my friend in Castlemaine, Australia for provoking a fascinating line of inquiry!


Further reading

From the start of the Chemical Revolution to Boussingault

Fathers of Meat Curing

Saltpeter:  A Concise History and the Discovery of Dr. Ed Polenske

The nitrogen cycle and meat curing


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(c) eben van tonder

Bacon & the art of living” in book form

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Notes

(1)  After a short service in the Woodstock house, the procession moved to the Groote Kerk where Jacobus has been an elder.  The coffin was carried into the church by the Cape premier, Cecil John Rhodes, Sir John Henry de Villiers (subsequent chief justice of the Union), JW Sauer, Onze Jan Hofmeyer, Sir Gordon Sprigg, Colonel F. Schermbrucker, ML Neetling and DC de Waal.

After the service the funeral procession moved to the Cape Town station, where a special train took the mourners to the Maitland Cemetery.  The coffin, of Cape teak, was lowered into the ground which Jacobus picked himself.

The grave was filled up and wreaths were laid on top.  One from David and Johanna Graaff, a second from John and Rosetta Graaff and a third from Jacobus and Susan Graaff. (Dommisse, E, 2011:  48, 49)

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Jacobus Combrinck’s grave in the Maitland Cemetery.
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The funeral procession would have walked along this path from the train tracks at the far top side of the picture to Jacobus’s grave on the right, under the tree, on the right.

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The affection from the Graaff brothers who were responsible for erecting the gravestone is evident.  At the top, the words, “Ter Dierbare Herinnering aan Jacobus A. Combrinck,” “For affectionate remembrance of Jacobus A. Combrinck.”

Under Jacobus’s birth date and date of passing, the inscription in Dutch reads, “Ik weet op wien te vertrouen,” “I know in whom to trust.”

Underneath is written in Dutch,”Opgericht door zyne dankbare neven de broeders Graaff,” “Erected by your grateful nephews, the brothers Graaff.”

David took over Jacobus’s position in the Legislative Council of the Cape Colony soon after his passing.

The following notice appeared in a colonial newspaper.

The_Colonies_and_India_Sat__Oct_10__1891_
A notice published on page 11 in The Colonies and Indian under the heading “Colonial, Indian and American News Items” on 10 Oct 1891.

(2) The Woodstock house was previously owned by a highly respected judge, Henry Cloete in the suburb of Papendorp (later to be renamed, Woodstock).  He enlarged it greatly.  The house was built on an estate where Jacobus planted trees, erected a water mill of his own design, cultivated a splendid flower garden.  (Simons, PB, 2000:  14)

(3)  Sir Gordon Sprigg, prime minister before Rhodes ousted him, was moved when he heard the news of Combrink’s death.  He said, “A good man has gone from among us.”  Rhodes apparently only slipped a posy of white and purple violets into his coffin and said nothing.  These two powerful men were never the best of friends. (Simons, PB, 2000:  27)

(4)  When doing trials at the then Vion Factory in Malton, Ken Pickles was the NPD (New Product Development) manager.  A young intern from Brazil would walk behind him and every time we went to the curing tanks, he would ask the young man this question.  It’s an image that I will never forget.

(5) An anaerobic organism or anaerobe is any organism that does not require oxygen for growth.

(6) Processed meats many times contain bacteria, many of which are responsible for changing nitrate to nitrite. “This conversion proceeds more rapidly in unpacked bacon than in the vacuum-packed variety, a difference which has been ascribed somewhat surprisingly to the low reducing activity of anaerobic bacteria. (Hill, MJ. 1991: 96)

(7) The nitrate and nitrite in salts are primarily responsible for the curing activity in meat. “The reduction of nitrate (NO3-) salts to nitrite (NO2-) and then to gaseous NO and its subsequent reaction with myoglobin to form the nitrosyl-myoglobin complex forms the basis for cured meat flavour and colour.

It was also later realized that it is bacteria that first converts nitrate into nitrite, which is the mechanism underlying in the preservation of food. Nitrite in meat is responsible for inhibiting the growth in aerobic bacteria (especially the spores of Clostridium botulinum), retard the development of rancidity during storage, develop and preserving the meat flavour and colour, stabilizing the oxidative state of lipids in meat products.” (Dikeman, M, Devine, C, 2014: 436)

(8)   The fact that nitrate is not the curing agent, but nitrite was in fact discovered soon asfter 1891.  One of the men at the forefront of these discoveries were Prof. D. R. Hoagland, professor of plant nutrition, University of California (www.nature.com).  He suggested in 1908 that the “reduction of nitrate to nitritenitrous acid and nitric oxide was by either bacterial or enzymatic action or a combination of the two and was essential for NOHb formation. The scientific knowledge led to the direct use of nitrite instead of nitrate, mostly because lower addition levels were needed to achieve the same degree of cure.” (Pegg, RB, Shahidi, F. 2000)

In keeping with our interest in the person and his discovery, the following notice was published at the death of Prof. Hoagland by the University of California.
“1884-1949

Dennis Robert Hoagland, Professor Emeritus of Plant Nutrition, died September 5, 1949. His life had been fruitful in achievement and stimulating in quality.

Professor Hoagland was born in Golden, Colorado, on April 2, 1884. He attended the Denver public schools and in 1903 entered Stanford University, graduating with an A.B. degree in the Chemistry major in 1907. After a fall semester of graduate work, he accepted a position at the University of California in January 1908 as Instructor in Animal Nutrition. From that time until his retirement June 30, 1949, with the exception of the period 1910 to 1913, his academic life was associated with the Berkeley campus.

About 1910 the U. S. Department of Agriculture became concerned with the alleged injurious effects of food preservatives on humans. A consulting board of scientific experts was set up and Professor Hoagland became a member of its staff. This assignment took him to the University of Pennsylvania where in addition to his research he found opportunity to continue his graduate studies in chemistry. It is evident that this early experience introduced him to the intriguing problems of biochemistry and this interest once developed became his major scientific concern the remainder of his career. In 1912 he accepted a graduate scholarship at the University of Wisconsin in the field of Animal Biochemistry, a field there cultivated with distinction by E. V. McCollum and E. B. Hart, and he was awarded the M.A. degree in 1913.

In the fall of 1913 he returned to California as Assistant Professor of Agricultural Chemistry. This area of knowledge, through the stimulating domination of Professor Hilgard, concerned itself with the soil and crop problems confronting California agriculture. Professor Hoagland found no difficulty in adapting himself to this new emphasis. It was probably his diversified early experience that made it possible for him later to develop on this campus a world center for the study of interrelated plant and soil problems. His broad interest did not lead him to scatter his efforts, however. He early demonstrated an ability to clearly outline a segment of the field and vigorously attack it, without restricting his vision of the entire complex problem. It was this quality which enabled him to achieve so significantly.

Professor Hoagland became head of the newly created Division of Plant Nutrition in 1922. Under his guidance and stimulation, this became more than a “Division” in the College of Agriculture: it was in effect what the Germans might have termed an “Institut für Pflanzen und Boden Wissenschaft.” It was a dynamic research center in which both basic and practical problems of plant oil interrelationships were studied with enthusiasm and insight; the laboratory was a magnet which drew students and mature investigators from all parts of the world. His own contributions to the research center’s activities were many and important. It was the early disclosure by himself and associates of the phenomenon of so-called “active absorption” of salts by living cells, both plant and animal, that compelled a complete reappraisal of salt absorption processes. His own research and that of his students led to new discoveries on the need and function of “trace” chemical elements–elements required by living cells in such minute amounts as to escape detection except by the use of the most refined techniques. These and other revelations constituted the leaven which activated investigations in many associated fields. His laboratory was a center with a radiating influence which reached out and touched other great scientific centers, and also the lone worker at an isolated post.

Professor Hoagland entered fully into the academic life of the University. He served as a member, then as chairman, of the Budget Committee and as a member of many other Senate and administrative committees. He was a member of numerous scientific organizations, including the National Academy of Science, and served on important national scientific boards. Many honors came to him. The American Society of Plant Physiologists presented him with the Stephen Hales Award in 1929; the annual $1,000 prize of the American Association for the Advancement of Science was given to him and an associate jointly in 1940. He was selected as Faculty Research Lecturer at Berkeley in 1942 and the same year delivered the John M. Prather Lectures at Harvard. In 1946 he was awarded the Barnes Life Membership in the American Society of Physiologists.

Professor Hoagland was married to Jessie A. Smiley in 1920. She died in 1933 leaving three sons, all of whom are graduates of this University. He did not possess a rugged constitution and the last few years of his life were marred by illness. But almost to the last he kept a faculty for keen appraisal of scientific and social situations and an interest in human events of the most diverse sort. He was a man of judgment, of tolerance, and of discernment, one who abhorred hypocrisy and admired honesty. He was the quality out of which great human structures are built.

W. P. Kelley D. I. Arnon A. R. Davis” (CDLIB)

(9)  Humus is decaying organic matter.  (Bynum, WF, et al, 1981:  300)

(10)  The trademark was granted in 1899 for Oxo.

(11)  The German chemist, Justice von Liebig (1803 – 73), continued to believe that plants got their nitrogen from the air (in the form of ammonia).  (Wikipedia, Justice_von_Liebig)  He has popularised a principle developed in agriculture science by Charl Sprengel (1828) and was called Liebig’s Law of the Minimum, often simply called Liebig’s law or the law of the minimum. It states that growth is controlled not by the total amount of resources available, but by the scarcest resource (limiting factor)  (Wikipedia, Law_of_the_Minimum)

(12)  He also attributed fermentation to microorganisms.

“Schwann is famous for developing a ‘cell theory’, namely, that living structures come from formation and differentiation of units (the cells), which then constitute the bodies of organisms (Schwann, 1839). His paper on fermentation (Schwann, 1837) was entitled ‘A preliminary communication concerning experiments on fermentation of wine and putrefaction’. Using a microscope, Schwann examined beer yeast and described it as resembling many articulated fungi and ‘without doubt a plant’. His conclusions from his observations and experiments were unequivocal, revolutionary and correct: The connection between wine fermentation and the development of the sugar fungus is not to be underestimated; it is very probable that, by means of the development of the fungus, fermentation is started. Since, however, in addition to sugar, a nitrogenous compound is necessary for fermentation, it seems that such a compound is also necessary for the life of this plant, as probably every fungus contains nitrogen. Wine fermentation must be a decomposition that occurs when the sugar-fungus uses sugar and nitrogenous substances for growth, during which, those elements not so used are preferentially converted to alcohol.

In one of his experiments, Schwann boiled some yeast in a solution of cane sugar in four stoppered flasks. After cooling, he admitted air into the flasks: for two flasks, the air was first passed through a thin red-hot glass tube (analysis showed this air still to contain 19·4 % oxygen); the other two flasks received unheated air. Fermentation occurred only in the latter two flasks. Schwann’s conclusion was important:Thus, in alcoholic fermentation as in putrefaction, it is not the oxygen of the air which causes this to occur, as previously suggested by Gay-Lussac, but something in the air which is destroyed by heat.

In this notable 1837 paper, Schwann anticipated observations made by Pasteur over twenty years later, writing:Alcoholic fermentation must be regarded as the decomposition effected by the sugar fungus, which extracts from the sugar and a nitrogenous substance the materials necessary for its own nutrition and growth; and substances not taken up by the plant form alcohol.

(Barnett, JA.   1998, 2000)

(13)  The chemist, Eduard Polenske (1849-1911) (Wikipedia. Pökeln), was born in Ratzebuhr, Neustettin, Pommern, Germany on 27 Aug 1849 to Samuel G Polenski and Rosina Schultz. Eduard Reinhold married Möller. He passed away in 1911 in Berlin, Germany. (Ancestry.  Polenske)  He was working for the German Imperial Health Office when he made the discovery about nitrite in curing brine. (Wikipedia.  Eduard_Polenske)

The Imperial Health Office was established on 16 July 1876 as a focal point for the medical and veterinary in Berlin. First, it was the division of the Reich Chancellery and since 1879 the Ministry of the Interior assumed. 1879, the “Law concerning the marketing of food, luxury foods and commodities” was adopted, including the Imperial Health Office was responsible for its monitoring.  Erected in 1900 Reichsgesundheitsrat supported the Imperial Health Office in its tasks.  (Original text:  “1879 wurde das „Gesetz betreffend den Verkehr mit Lebensmitteln, Genußmitteln und Gebrauchsgegenständen“ verabschiedet, für dessen Überwachung unter anderem das Kaiserliche Gesundheitsamt zuständig war.”) (Wikipedia.  Kaiserliches Gesundheitsamt)

The spelling of his surname varies between Polenski and Polenske.

(14) “This prophetic insight into the continual renewal of body constituents, differing in rate in different tissues, succumbed to the theories of Liebig, Voit, Folin and others, and was not regained until more than a century later when Schoenheimer’s publication in 1942 of “The Dynamic State of Body Constituents” demonstrated the instability of tissue components by isotopic means.”  (Munro and Allison, 1964)

References

Barnett, JA.   1998, 2000.  Extract from lectures.  Beginnings of microbiology and biochemistry: the contribution of yeast research.  http://mic.sgmjournals.org/content/149/3/557.full

Bynum, WF, Browne, EJ, Porter, R.  1981.  Dictionary of the History of Science.  Princeton Legacy Library.  Macmillan Press.

Craine, JM.  2008.  Resource Strategies of Wild Plants.  Princeton University Press.

Danchin, A.  From Lamarck to Semmelweis, Transformation of chemical biology1800 – 1849:  http://www.normalesup.org/~adanchin/history/dates_1800.html

Dommisse, E. 2011.  First baronet of De Grendel.  Tafelberg.

Associative and Endophytic Nitrogen-fixing Bacteria and Cyanobacterial …

Elmerich, C, Newton, WE.  2007.  Associative and Endophytic Nitrogen-fixing Bacteria and Cyanobacterial Associations.  Springer.

Laufer, B.,  1919, Sino-Iranica, Field Museum of Natural History, Publication 201, Anthropology Series Vol XV, No. 3

Myers, RL.  2007.  The 100 most important chemical compounds.  Greenwood Press, Westport.

Pennsylvania Packet, Friday, 18 August 1786

Schofield, RE.  2004.  The Enlightened Joseph Priestly.  The Pennsylvanian State University

Smith, Edward.  1876. Foods. D. Appleton and Company, New York.

Simons, Phillida Brooke. 2000. Ice Cold In Africa. Fernwood Press

Smil, V.  2001.  Enriching the Earth.  Massachusetts Institute of technology.

Waksman, S. A..  1927.  Principals of Soil Microbiology.  Waverly Press.

Zumbal. 2000. Chemistry, 5th edition.  Houghton Mifflin Company.

https://www.boundless.com (Early Discoveries Nitrogen Fixation)

http://en.wiktionary.org/wiki/azote

http://en.wikipedia.org/wiki/Horace-Benedict_de_Saussure

http://en.wikipedia.org/wiki/Justus_von_Liebig

http://en.wikipedia.org/wiki/Claude_Louis_Berthollet

http://en.wikipedia.org/wiki/Nitrogen_cycle

Pictures

Figure 1:  From Simons, Phillida Brooke. 2000. Ice Cold In Africa. Fernwood Press, page 9.

Figure 2:  http://fletchingtonfarms.wordpress.com/

Figure 3:  http://today.uconn.edu/blog/2011/09/the-evolution-of-biology-at-uconn/

Figure 4:  http://web.mit.edu/cheme/about/history.html

Figure 5:  From http://www.foodhistory.com/foodnotes/road/cwf1/

Figure 7 – 9:  Photos of Combrinck’s grave by Eben.

Figure 10:  The Colonies and Indian, 10 Oct 1891, p 11.

 

Chapter 08.06 From the Sea to Turpan

Introduction to Bacon & the Art of Living

The quest to understand how great bacon is made takes me around the world and through epic adventures. I tell the story by changing the setting from the 2000s to the late 1800s when much of the technology behind bacon curing was unraveled. I weave into the mix beautiful stories of Cape Town and use mostly my family as the other characters besides me and Oscar and Uncle Jeppe from Denmark, a good friend and someone to whom I owe much gratitude! A man who knows bacon! Most other characters have a real basis in history and I describe actual events and personal experiences set in a different historical context.

The cast I use to mould the story into is letters I wrote home during my travels.


From the Sea to Turpan

University Geology Museum (1), Copenhagen, June 1891

The day has finally arrived, our much-anticipated visit to the University of Copenhagen’s Geology Museum.  It is located on Nørregade. The museum is part of the Natural History Museum of Denmark.  It was truly exceptional.  The exhibition of minerals is, from what I am told, one of the finest in Europe!  There are exhibitions on meteorites, volcanoes, continental drift, the geology of Denmark, the geology of Greenland, fossils (including the largest bivalve including clams, mussels, oysters, and scallops in the World), and the origin of humans.  The fact that we had to postpone the trip for a week worked out well.  Despite Uncle Jeppe being unable to join us, the Curator of the Museum was there and what happened was exceptional!  He proved to be just the man to bombard with my many questions!

turfan
Bezeklik caves on mountain slopes near Turfan

Wondering About Meat Preservation

For as long as I can remember, I have been wondering about meat curing.  As a child, I tried to imagine how people discovered that dry meat lasts longer.  It seems self-evident to us now, but someone had to “discover” it!    There is a difference between dry meat and cured meat.  Cured meat is identified by three things.  Its look, taste, and longevity.  When an animal is killed, the meat blooms a beautiful red colour.  If you do not rub it with saltpeter, it changes to a dull brown colour.  If you, however, rub it with a mixture of salt and saltpeter, it retains the pinkish-reddish colour.  If you rub it onto meat that already turned brown, after a few days the entire piece of meat will return to its pinkish-reddish colour, resembling fresh meat.  This probably conjured up images of the power of immortality in the minds of the ancients endowing saltpeter with seemingly magical powers.

Is Curing possible without Saltpeter

Using saltpeter does not guarantee you of good bacon, but without it, curing does not happen.  When you dry meat, this can be done without saltpeter and the meat will also last a long time but the meat will be dry and without juices.  In South Africa, the old Dutch farmers fused their knowledge of drying meat in the chimnies in Holland and the North European practice of using vinegar in their hams with the indigenous practice of hanging meat out in the sun and wind to dry.  They add coriander with salt to the vinegar to create what they call biltong.  This is a good example where drying works well to preserve meat with or without saltpeter.  Saltpeter can only be left out of the recipe if vinegar is used and lots of salt and provided that the temperature where the meat is hung is not too high.

It is possible to cure meat with salt only, but the process takes a very long time.  Longer even than dry-curing with saltpeter.  It is very difficult.  Communities in Italy that does this often times have to carry the hams or bacons higher up the mountain to parts where it is still cold if the weather turns warmer.  For our curing plant in Cape Town, similar to Uncle Jeppes’ plant, time is a luxury that we will not have and besides, we do not have the luxury of very high mountains.  The process of curing it without saltpeter is such a specialty field that I will write to you about it separately.

The Friendly Curator and My Research Partner

The curator of the museum was on duty this weekend which was must fortuitous.  He agreed to have coffee with us and answer our questions.  This is the thing about the Danish that I notice wherever I go – they don’t have inflated egos.  If this was in Cape Town, I can not imagine that someone with his position would have taken the time to have coffee with us and answer a novice to the area minerals and chemistry’s many questions.

Minette is a research partner second to none!  She asks simple but powerful questions.  She is never afraid to ask for clarification on points of seeming contradiction.

From Sea to Dry Deserts

The curator patiently listened to my questions before he started speaking.  It was as if he did not really listen to my questions but decided to rather address the topic of the origins of curing more generally.  Not one of s minded his approach.  it was all fascinating and he had Minette, Andreas, his dad, his mom and me hanging on his every word.

First, the professor had to set me right in a wrong perception I had about how salts naturally occur on earth.  I did not understand is that today our salts are very refined.  Impurities are removed before it is sold.  Different salts are neatly separated but in nature that is not how they occur.  Salts occur in nature as a mixture of various minerals.  When the ancients talk about saltpeter, for example, there were many different grades of purity.  The nitrate salts may be mixed with what we refer to as table salt or sodium chloride along with many other chemical compounds.  The opposite also occurs.  If salt is mined from a salt pan, for example, there may be small amounts of nitrate salts mixed in with the table salt.  There may even be some nitrite salts present in very small quantities from game urinating in the pan.

After setting me straight, the professor continued.  “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 has the same ability.”

“It is possible that curing was first noticed by early seafarers: meat proteins contain nitrogen.  When the meat is placed in seawater, the surface proteins start to break down and forms nitrites for a period of 4 to 6 weeks. Nitrite is then converted to nitrate over the next 4 weeks though bacteria. It is possible that they preserved meat in seawater barrels and that the whole process of curing was discovered accidentally.”

Our friendly curator ordered a second cup of strong coffee!  We all remained spellbound.  My note-keeping was put to the test and there was no time for me to even take a sip of coffee!  I had to keep up and did not want to miss a single point.

“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 doesn’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.”

Sal Ammoniac

He then introduced me to something that I did not expect.  Another curing salt!  “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.”

I was riveted!  “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 humans 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 compared to salting the meat with normal table salt.  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 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.”

“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.”

He then introduced us to a region of the word that I did not even know existed.

“Turpan is the name of an oasis in the far western regions of China.  It is an extremely dry area.  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.  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 Turfpan 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 related to meat curing may have come from Austria.  Whether it was Salzburg or Turfan is not clear.”

“Around Turpan (also called Turfan), Sal Ammoniac 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.  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.”

“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 tastes like since it was added to my favourite Dutch candy “Zoute Drop” with licorice.”

Flaming Mountains.jpg
Flaming Mountains of Turfan

More Information on 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 1600s 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 1500s 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 nitron 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 1750s, 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 world’s saltpeter production during the latter part of the 1700s.”

“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 that 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.  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 India 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 1300s.  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 development 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.”

“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. This correlates well with the proposed time when it became generally available to the European population as the 1700s 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.”

Everyone sitting around the table was hanging to his every word. I did not notice but by this time a small crowd had gathered around us.  The curator raised his voice slightly to allow everyone to hear.

“Meat curing, of course, there is another form of meat curing that I can tell you about.” As he started, Minette jabbed me in the ribs.  “You see!” she said!  “I told you!”  Minette asked me before why the sweat of horses is also called saltpeter which is exactly the subject that he brought up.

Horse Sweat

“It may surprise you that one of the techniques used by ancient horseback riders to cure their meat was to hang strips over the neck of the horse or placing it under your saddle so that the sweat of the horse cure the meat. We now know that sweat contains nitrates and the same bacteria that reduce the nitrate to nitrite or that remove the one oxygen atom from the Salpeter to form nitrite is present no horses.  This would result in the rapid curing of the meat.  The fact that meat was placed under the saddles shows the importance of “softening the meat” in a time when people did not have many options in caring for their teeth.”  It is the same mechanism, just in a less culturally acceptable way.”

“German and Austrian cookbooks pre-1600’s reveal that vegetable dyes were used to bolster colour 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 no doubt due to the effect of sal ammoniac on taste, it fell out of common use.  Hanging meat around the nacks of horses also had a limited lifespan in terms of popularity and as the availability of nitrate salts in Europe increased due to its use as a pharmaceutical and for military usage in gunpowder, the nations of Europe and China reverted to salt curing and today it is generally used globally.  In fact, most people will say that it has always been the curing salt of choice.”

An Unforgettable Day

It was all over too soon.  When the Curator of the Geology Museum was done, everybody applauded!  I asked him how he knows so much about meat curing and not only geology and mineralogy.  He told me that he grew up in a butcher’s family.  His dad had a keen interest in mineralogy in particular since it deals with chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. The reason why he studied geology was because of his father’s inspiration.

That evening we did not read from Edward Smith’s book after supper.  Instead, we went over the notes I took and where our host was too fast for me to catch everything he said, Minette, especially, helped me to get the facts straight.  She has a very keen mind and a great memory.

We talked till very late into the night and all retired to bed, continuous that we all experienced something very special today. There were two groups of people that I wanted to share this with.  Tristan, Lauren, I could not go to bed without writing this letter and I sat alone in my room writing this.  It is now 2:00 a.m..  Tomorrow I will share this with the second group of people or as in this instance, a person.  Jeppe could not attend on account of the birthday celebrations of a grandchild.  I can hardly wait for Minette and me to share this with him.

Now I am off to bed!  I am exhausted but insanely excited!  My Danish experience had just gone to another level!  I can hardly believe the privilege I have to be here!

Lots of love from Denmark and a very happy father!

Dad

Turfan Depression.jpg
Turfan depression

Further Reading

From The Salt Bridge,

01. Salt – 7000 years of meat-curing

02. Nitrate salt’s epic journey: From Turfan in China, through Nepal to North India

03. And then the mummies spoke!

04. The Sal Ammoniac Project

05. An Introduction to the Total Work on Salt, Saltpeter and Sal Ammoniac – Salt before the Agriculture Revolution


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Note 1

Neither the University of Copenhagen, the Geology Museum or any other affiliated organisation had no input in any of the content in this chapter.  All research and conclusions are that of Eben van Tonder and the interaction with the curator of the museum, as portrayed here, is fiction.  Eben places it in this setting for literary and artistic reasons.

References

Bacon Curing – A Historical Review

Photo References

Featured Image: Bezeklik caves on mountain slopes near Turfan.  https://www.advantour.com/china/turpan/bezeklik-caves.htm

Flaming Mountains of Turfan:  https://za.pinterest.com/pin/334251603567115799/?lp=true

Turfan Depression:  http://www.howderfamily.com/blog/turpan-depression/

Chapter 08.04 The Saltpeter Letter

Bacon & the Art of Living 1

Introduction to Bacon & the Art of Living

The quest to understand how great bacon is made takes me around the world and through epic adventures. I tell the story by changing the setting from the 2000s to the late 1800s when much of the technology behind bacon curing was unraveled. I weave into the mix beautiful stories of Cape Town and use mostly my family as the other characters besides me and Oscar and Uncle Jeppe from Denmark, a good friend and someone to whom I owe much gratitude! A man who knows bacon! Most other characters have a real basis in history and I describe actual events and personal experiences set in a different historical context.

The cast I use to mould the story into is letters I wrote home during my travels.


The Saltpeter Letter

June 1891

Dear Children,

The days grow ever more light and joyful as summer approaches. The cornerstone of meat curing is Saltpeter and understanding its composition and function in meat is the starting point to unravel the mysteries of bacon.  Curing is a separate discipline to fermentation such as is used in making salamis and drying, such as is used in biltong.  Saltpeter is what cures meat.  It is the overarching and controlling mechanism in bacon production.  My mind drifts back to Cape Town when I see the Danes going about their business of being Danish! Similar to saltpeter in bacon there are principles that make this great nation who they are.  Traditionally, their work ethic, their view of the equality of all humans, their model of cooperation are not just good ideas.  It is fundamental to their existence as people.   We have similar beliefs that make us who we are as an emerging nation.  Certainly, religion shaped our society in South Africa.  I remember the last church service at the Groote Kerk in Cape Town before I left on my grand quest.

It is in the same church where my mom and dad were married and where I was christened as a baby. As staunch Calvinists, much of life revolved around church and the Groote Kerk was my second home.

1910 photograph – sent to Schalk LE ROUX from Marthinus van Bart Photographer: Unknown

It was the first Christian place of worship in South Africa. The oldest church structure on this piece of land dates back to 1678, 26 years after the Dutch landed to set up their refreshment station. The current building was built by the German architect Herman Schuette in 1841. Much of the old church, including the steeple, was retained in Schuette’s new design. It is situated right next to parliament. The last Sunday before I left for Europe, my kleinneef preached.

He is a gentle man with a large pastorly heart.  His theology is progressive and his faith sincere.  My mom and dad are close to Oom Giel and his Brother, Oom Sybrand. They are my mom’s cousins.

That particular morning his text was Ephesians 5. I remember hearing the horse carts rattling by in the street outside church down Adderly street. As always, there was energy in the air as people arrived. Oom Jacobus and the Graaff kids who lived with him sat in their own allocated seating. He hung his hat on the rack provided for every congregant.

Oom Giel’s thesis was  “Live as people of the light.”  Here, at the Groote Kerk, the people who started the Cape Colony worshiped and receives their spiritual direction.  Oom Giel stressed that we receive the light, but he was humble about what that means. As a theologian, he was ahead of his time.  “A day will come when we realise that the church does not have all the answers.  One day the church will no longer be able to scare non-believers into faith by the threat of hell.  The light we received is that we are in God’s hands. Its a way of life.”

Deep-seated Calvinism shaped the colony. From the straight roads and square corners on neat houses to straight orchards. They believed God was in the first place viewing life as a geometer and this shaped everything they did. The Groote Kerk is the spiritual spring of the Colony.

It was not only an obsession with geometry that bewitched those who drank from the well and a misplaced superiority complex over all of God’s world, but good was also distilled from these waters. A friend from further up in Africa pointed it out to me one day when he visited Cape Town and I took him around to see the beautiful city. A mindset prevails among its inhabitants that says, we are here and we can thrive! We can get many things from Europe, but by golly, we can do it ourselves! What we can do is any time as good as the best we can get from Europe! With discipline and diligence, inherent to the Christian gospel, we approach every task set before us! In straight lines!  This is exactly the reason why I am in Denmark.  An inherent belief that whatever the Europeans can do, we can do better!

Apart from this, people from southern Africa mind our own business and desire a quiet life. We want to live in light of our gospel.  That is how Oom Jacobus, another one of my mentors, approaches life. How he cut his meat and wrap it for customers; cure the bacon; grew his spices in his enormous garden at his home in Woodstock, these are all outworkings of his fundamental view of life.

As Oom Giel lead us in reciting the Apostolic Creed, I wondered, how many times through the years was it recited in this Church!  The settlers, for all their faults – many of them were bound by this confession and tried to live true to its articles.

Oom Giel broke the bread. It is communion with the body of Christ. And so is the wine, union with the blood of Christ.  Our rituals and confessions link us to countless generations. Past and present and from these deeply held beliefs we became. I am in Denmark to learn the art of meat curing, like Uncle Jacobus.  The last Sunday in Cape Town, I listened to Oom Giel with Uncle Jacobus and David de Villiers Graaff in attendance.  What a special day!

Now I am learning another gospel in Denmark. The art of curing bacon and the salt we use is saltpeter.  That day at the Groote Kerk Minette was also there.  We sat together and shared communion.  Today it is Sunday and again, Minette is here with me.  It is a surprise I never expected!  She arrived last weekend and Uncle Jeppe returned from Liverpool during the week.  This morning she joined me at his bacon factory.

Uncle Jeppe reminded me of Oom Giel when he leaned forward in his chair pressing down on his desk. Passion for the subject. Authoritative. Uncle Jeppe must have been quite a ladies man in his day!  He made Minette feel very welcome and gave her the grand tour of the factory.  At lunchtime, I was already sitting in his office waiting for them.

They walked in while Uncle Jeppe and Minette were laughing at a joke.  They do not share the joke with me.  “So, today we go back to a time when saltpeter was still a mysterious compound,” Uncle Jeppe said.  Minette took the seat beside me.  Uncle Jeppe walked to behind his desk where he took a notebook out of a drawer.  He does not sit in his cair but walks around the desk and sits on it facing us.  “The story of saltpeter goes back, ions of time!”

Minette interjected that she still remembers exactly how it is formed.  She looks at me when she recounts it.  “Nitrogen Dioxide (NO2), formed in the atmosphere when nitrogen reacts with ozone, reacts with raindrops which is water or H2O.  The two oxygen atoms of nitrogen dioxide combine with the one from water to form 3 oxygen atoms bound together.  There is now one nitrogen atom bound to three oxygen atoms to give us NO3 or nitrate.  There is still one hydrogen atom left and it combines with the nitrate to form nitric acid (HNO3).  Nitric acid falls to earth and enters the soil and serves as nutrients for plants.”

“In the ground,” I finish her thought, “it reacts with a salt such as potassium, calcium or sodium to form potassium nitrate, calcium nitrate or sodium nitrate which is taken up as plant food.”  I smiled at her.  “You remember well!”

Uncle Jeppe smiled.  He almost got lost in the moment.  He pulled himself back to reality and opened his notebook.  He balanced the open book in his one hand.  He is a meticulous note keeper,  something that I learned from him.  He keeps notes written in his neat cursive handwriting. One can see that he values every sentence he writes!  I now have my own notebook and on Sundays, I review the work e covered that week and I write what I learned or saw in my letters to you guys.

Saltpeter is one of the magical salts of antiquity. For most of human history, we did not know what saltpeter was,” Jeppe preached on. Saltpeter was used in ancient Asia and in Europe to cool beverages and to ice foods. There are reports dating back to the 1500s about it. Without any doubt, it has been known for millennia before it was reported on in writing. (Reasbeck, M:  4)

From antiquity the ancient cured their meat with it and enjoyed its reddening effect, it’s preserving power and the amazing taste that it gives.  The earliest references to it go back to people in Mesopotamia from the Bronze Age who used it in the same way as the Romans. The characteristic flavor it imparts to meat was reported on in 1835 (Drs. Keeton, et al;  2009) but there can be little doubt that it was noticed since many thousands of years before the 1800s.

The Chinese worked out how to make explosives, using the power of saltpeter. There is even a record of gunpowder being used in India as early as 1300 BCE, probably introduced by the Mongols. (Cressy, David, 2013:  12)  People started using it as a fertilizer when overuse of the land required us to replenish the nutrients in the soil.”

It was widely known traded in markets in China, India, the Middle East, North Africa, Europe, and England. It was its use by the military in gunpowder and its pharmaceutical use made it generally available in Europe from the 1700s. This meant its usage as curing agent with salt increased and by 1750 its use was universal in curing mixes in Europe and England. Most recipe books from that time prescribed it as a curing agent. (Drs Keeton, et al, 2009)

Despite its wide use by 1750, people still could not work out if saltpeter occurred naturally or was it something that had to be made by humans.   When they managed to get hold of it, they wondered how to take the impurities out of the salt which gave inconsistent curing results and was no good in gunpowder. People were baffled by its power.

“Some speculated that it contained the Spiritus Mundi, the ‘nitrous universal spirit’ that could unlock the nature of the universe!”

Jeppe quoted Peter Whitehorney, the Elizabethan theorist who wrote in the 1500s.  He said about saltpeter, “I cannot tell how to be resolved, to say what thing properly it is except it seemeth it hath the sovereignty and quality of every element”.

Paracelsus, the founder of toxicology who lived in the late 1400s and early 1500s said that “saltpeter is a mythical as well as chemical substance with occult as well as material connections.” The people of his day saw  “a vital generative principle in saltpeter, ‘a notable mystery the which, albeit it be taken from the earth, yet it may lift up our eyes to heaven’”   (Cressy, David, 2013:  12)

Jeppe got up and settled in on his large office chair.  He leaned back as he continued to read.  “From the 1400s to the late 1800s we have records of almost every scientist probing and testing it to determine its properties. No doubt, ancient scientists and stone age chemists did the same for many thousands of years and in a way, it is the fascination with enigmatic salts that precipitated the science of chemistry.”

“Saltpeter encompassed the “miraculum mundi”, the “material universalis” through which ‘our very lives and spirits were preserved.  Its threefold nature evoked ‘that incomprehensible mystery of … the divine trinity,’ quoting Thomas Timme who wrote in 1605, in his translation of the Paracelsian Joseph Duchesne.  “Francis Bacon, Lord Chancellor and Privy Councillor under James I, described saltpeter as the energizing “spirit of the earth.””   (Cressy, David, 2013:  14)

“Robert Boyle who did experiments trying to understand saltpeter found it, ‘the most catholic of salts, a most puzzling concrete, vegetable, animal, and even mineral, both acid and alkaline, and partly fixed and partly volatile.  The knowledge of it may be very conducive to the discovery of several other bodies, and to the improvement of diverse parts of natural philosophy” (Cressy, David, 2013:  14)

I could tell that Minette loved it!  We were both riveted to every word!  When I saw her interest in the subject, I realised that in Minette I, not only have a friend and a beautiful friend at that, but I have a partner to explore life with me.  She not only laves nature and exploring our natural universe, but she also has an amazingly inquisitive mind in all matters technical.  “Cheepes, I thought, what a woman!”

Tristan, Lauren, I was completely dumbstruck!  On the one hand was the realisation that there are bonds between Minette and me that are stronger than simply a friendship.  On the other hand, there is the realisation that the salt that I have been using to cure pork for most of my life is one f the greatest salts from antiquity!  I used it with my Dad and Oupa Eben on the farm every time we cured Kolbroek meat.  Here in Denmark, I work with it every day!  I was overcome by a feeling of deep respect for this chemical compound that we readily use. Even now that we know saltpeter is a salt attached to an acid in the form of one nitrogen atom and three oxygen atoms (CaNO3), its history is remarkable! I stepped onto a stage where a Shakespearean drama has been acted out and I became part of a grand history.  I would never again hold it in my hand and think of it in the same way!  Saltpeter is far more than just its chemical composition!  Contained in its essence is the spirit of every man and woman who ever looked at it to unravel its secrets for thousands of years.

I recall Oom Giel’s sermon.”Live as people of the light. Be true to your most basic quality.” For millennia, saltpeter mesmerized us long before its essential nature could be explained. Oom Giel’s message was the same. Mesmerize others with your essential Christian character. There should be no need for debate or discussion.

It is late in the Østergaard family home. Andreas, his dad, mom, Minette and I were discussing Uncle Jeppe’s lessons from today after supper. They told us about a museum dedicated to geology in Copenhagen and they are planning to take us there next weekend where I intend exploring the question of the origins of saltpeter more closely. The question of who were the first people to change the use of saltpeter into an art? Who harnassed its use and who established what is now the collective knowledge of saltpeter into an art.  The art of curing meats.  Who were the custodians of its power for millions of human history?  I intend exploring this question with the good people from the University next weekend!

Both Minette and I are insanely excited. The house is now quiet with everybody asleep except me, wrapping the day up with my customary letter to you guys.  I love you more than life itself and cant wait to share what we learn from the University next weekend.

Lots of love,

Dad


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References

Cressy, D.  2013.  Saltpeter.  Oxford University Press.

Cressy, D.  Saltpetre, State Security, and Vexation in Early Modern England.  The Ohio State University

Crookes, W.  1868/ 69.The Chemical News and Journal of Physical Science, Volume 3.  W A Townsend & Adams.

Deacon, M;  Rice, T;  Summerhayes, C.  2001. Understanding the Oceans: A Century of Ocean Exploration,   UCL Press.

Dunker, CF and Hankins OG.  October 1951.  A survey of farm curing methods.  Circular 894. US Department of agriculture

Frey, James W.   2009.  The Historian.  The Indian Saltpeter Trade, the Military Revolution and the Rise of Britain as a Global Superpower.   Blackwell Publishing.

Jones, Osman, 1933, Paper, Nitrite in cured meats, F.I.C., Analyst.

Drs. Keeton, J. T.;   Osburn, W. N.;  Hardin, M. D.;  2009.  Nathan S. Bryan3 .  A National Survey of Nitrite/ Nitrate concentration in cured meat products and non-meat foods available in retail.  Nutrition and Food Science Department, Department of Animal Science, Texas A&M, University, College Station, TX 77843; Institute of Molecular Medicine, University of Texas, Houston Health Science Center, Houston, TX 77030.

Kocher, AnnMarie and Loscalzo,  Joseph. 2011.  Nitrite and Nitrate in Human Health and Disease. Springer Science and Business Media LLC.

Lady Avelyn Wexcombe of Great Bedwyn, Barony of Skraeling Althing
(Melanie Reasbeck), Reviving the Use of Saltpetre for Refrigeration: a Period Technique.

Mauskopf, MSH.  1995.  Lavoisier and the improvement of gunpowder production/Lavoisier et l’amélioration de la production de poudre.  Revue d’histoire des sciences

Newman, L. F.. 1954.  Folklore. Folklore Enterprises Ltd.

Pegg, BR and Shahidi, F. 2000. Nitrite curing of meat. Food and Nutrition Press, Inc.

Shenango Valley News (Greenville, Pensylvania), 26 January 1883

Smith, Edward.  1876. Foods. D. Appleton and Company, New York.

Schaus, R; M.D. 1956.  GRIESS’ NITRITE TEST IN DIAGNOSIS OF URINARY INFECTION,    Journal of the American Medical Association.

http://hansard.millbanksystems.com/commons/1938/mar/01/meat-prices

Photo credits:

The 1910 photo of the Groote Kerk, from https://www.artefacts.co.za/main/Buildings/bldg_images.php?bldgid=6457#25001

All other photos by Eben van Tonder

Factors Affecting Colour Development and Binding in a Restructuring System Based on Transglutaminase

Factors Affecting Colour Development and Binding in a Restructuring System Based on Transglutaminase.
By: Eben van Tonder
1 June 2018

The articles on the complete bacon production system are available in booklet form:    https://tgrestructuringofmeat.pressbooks.com

INTRODUCTION

I started experimenting with Ajinomoto’s Activa almost 5 years ago.  In preparation for that, I wrote an article, Restructuring of whole muscle meat with Microbial Transglutaminase – a holistic and collaborative approach, which I updated over the years.

I have been approached by countless people from around the world with questions and insights which I did not address in my initial article.  I continued to gather bits of information, stored in mails to myself, learn from production managers I got to know in every part of the world and great articles I discovered over the years as I worked on a daily basis to do first-hand experiments at Woody’s and I tried to answer these questions for myself and for others while, always, working on improving the system.

It is time for a completely new follow up article where I address these issues systematically.  I look at heat treatment, colour development, moisture loss, protein denaturing, phosphates, salt, deboning, meat quality, pressure, freezing, chilling and gelation in relation to the use of TG.  I continued to look at what an optimal TG blend will look like and the aspects that our production systems must incorporate.  I also examine possible future developments in thermal processing and a few alternative ways to set up a production line where TG is incorporated into a grid system for the restructuring of large meat muscles, mainly for the production of bacon.

The number one question I was asked over the years is if TG affects meat colour.  Some researchers reported slight colour changes on fresh meat, but as far as processed meats are concerned, it is an irrelevant question since there are much more important factors affecting colour than the small impact that TG may or may not have.  Lets very briefly look at heating, colour development, and moisture loss to illustrate my point.

We begin with a review of the curing process and the effect of heat and smoke on colour development and moisture loss before we turn our full attention to a discussion of other factors affecting TG.

PROPER COLOUR DEVELOPMENT BEGINS WITH CURING:  THE IMPORTANCE OF RESTING, AFTER INJECTION, BEFORE SMOKING

CodeCogsEqn (11) to CodeCogsEqn(8) to NO 

When sodium nitrite is placed in solution in the brine preparation phase, the crystal structure breaks up and the ions separate into Na and CodeCogsEqn (4).  Nitrous acid is formed.    This hydration of nitrous acid is an important time-consuming reaction (Krause, B. L.; 2009: 9).

After the formation of nitrous acid (CodeCogsEqn (11)), the next step “is the generation of either a nitrosating species or the neutral radical, nitric oxide (NO).”  (Sebranek, J., and Fox, J. B. Jn.; 1985:  1170)  A nitrosating species is a molecular entity that is responsible for the process of converting organic compounds into a nitroso (NO) derivatives, i.e. compounds containing the R-NO functionality.  During resting, the most important one is the formation of Nitrosyl Chloride (NOCl). This is one of the good reasons why leaving out salt from bacon curing is not advisable.  The time-consuming nature of these reactions is also the reason why a resting phase is vital.

In a large commercial high-throughput bacon curing plant we found that an optimal processing sequence has the following sequence.  A few variations of this basic model will be proposed in this article, but this is the model that I used with great effect for many years and other models, if they survive critical theoretical scrutiny, needs to be tested.

  • injecting the meat,
  • tumbling it,
  • resting it for between 12 and 24 hours (depending on the curing room temperature),
  • tumbling it again to pick up brine that leached out during the maturing or colour development stage and,  This time, add TG blend.
  • grid filling
  • smoking/Thermal Treatment
  • de-gritting
  • blast freezing
  • equalizing
  • slicing and packing

Lets now focus on colour development during smoking and thermal treatment to understand optimal smoker chamber temperatures.

PROPER COLOUR DEVELOPMENT:  THE IMPORTANCE OF SMOKING

Cold smoking is normally seen as smoking where the core temperature will remain below 35 deg C.  We use hot smoking where the core temperature riches > 35 deg C but < 45 deg C.  Smoking and thermal treatment are therefore considered jointly.  Temperature effects product taste, meat toughness, binding, coulour, and moisture loss.

Reddening

During reddening, the temperature is increased, extraction flaps in the smokehouse closed to maintain humidity, and sulfhydryl groups are released which is a reducing substance in meat and important in proper cured colour formation.  Fraczak and Padjdowski (1955) indicated that 80°C is the critical temperature for the decomposition of sulfhydryl groups in meat.” (Cole, 1961)  (Reaction sequence)

Smoking

During heating and smoking, there are several changes in the meat that has a direct effect on the colour development.  The nitrosating species that is more dominant than NOCl is smoke due to the presence of phenolic compounds.  In addition to the heat release of sulfhydryl groups, the pH is reduced in the meat.  Randall and Bratzler (1970) noticed an increase in the myofibrillar protein nitrogen fraction, pH and free sulfhydryl groups of pork samples that were only heated, and a decrease of these values in the samples that were subjected to heat and smoke. “Results of this study indicated that smoke constituents react with the functional groups of meat proteins.” (Randall, 1970)  These results seem to support a reddening step before smoke is applied due to the fact that heating would release the sulfhydryl groups and during the smoke steps, the pH will be reduced.  (Reaction sequence)

DENATURING VS COAGULATION

With our consideration of smoking on meat, we have also entered the discussion of the effect of heat on meat.  Before considering the effect of heat on the protein lets first see how the heat gets to it.

Mechanism of heat transfer

Heat is transferred during cooking through conduction, convection, and radiation.  “Spakovszky and Greitzer (2002) defined conduction as ‘transfer of heat occurring through intervening matter without bulk motion of the matter,’ convection as heat transfer due to a flowing fluid, either a gas or a liquid, and radiation as ‘transmission of energy through space without the necessary presence of matter.’   Radiation can also be important in situations in which an intervening medium is present, such as heat transfer from a fire or from a glowing piece of metal (Spakovszky and Greitzer 2002).”  (Yu, T.Y., et al, 2017)

“Meat cooking usually involves more than 1 mode of heat transfer (Bejerholm and others 2014).”   During cooking in a smokehouse, heat treatment is achieved through dry heat surrounding the meat, but during reddening and smoking the air is or become moist and moist-heat (hydrothermal) thermal processing uses hot steam. Smoke House thermal treatment, including smoking, is, in reality, a combination of dry heat and moist heat.  (Yu, T.Y., et al, 2017)

“Conventional cooking of meat results in heterogeneous heat treatment of the product on account of steep temperature gradients (Tornberg 2013). Emerging mild cooking techniques such as ohmic cooking can achieve a more homogeneous heating by heating the entire volume of meat at the same time (Tornberg 2013).”  (Yu, T.Y., et al, 2017)  THis is an important point for consideration in a continuous, fully automated system.

This is important in considering the effect of heat on the grid system with holes.   The present role to steel ratio is 1:1,8.  The exposed meat area is therefore approximately half (take the edging to be approximately 0.02 to give the total ratio of 1:2).  This amplifies the effect of heating, but by what factor? This needs to be determined experimentally between different smokehouses.  I have determined a variety of different options in smokehouse settings over the years.

“Heat may cause proteins to lose their native conformation (denature) by providing the polypeptides with kinetic energy, increasing their “thermal motion,” and thus rupturing the weak intramolecular forces (such as nonpolar interaction, various kinds of electrostatic interaction, and disulfide bonds) that hold the proteins together (Davis and Williams 1998). As the temperature increases, a protein starts to unfold. When almost all the tertiary and secondary structures are lost, the unfolded protein may aggregate, have its disulfide bonds scrambled, undergo side-chain modifications (Davis and Williams 1998), and cross-link with other polypeptides. Aggregation is the consequence of nonpolar interaction between heat-denatured proteins whose hydrophobic groups have turned outward into the surrounding water, in order to adopt a lower energy state (Davis and Williams 1998). A variety of side-chain modifications, such as those induced by oxidation or the Maillard reaction, have been characterized in proteins following heat treatment.”  As heat increases, the 3-dimensional structure of meat proteins change.  These changes manifest in a change in colour and gelation.  (Yu, T.Y., et al, 2017)

DEVELOPMENT OF NITROSYLMYOCHROMOGEN

“Upon thermal processing, globin denatures and detaches itself from the iron atom, and surrounds the hem moiety.  Nitrosylmyochromogen or nitrosylprotoheme is the pigment formed upon cooking and it confers the characteristic pink colour to cooked cured meats.”  (Pegg, R. B. and Shahidi, F; 2000: 42)

We also need to review the main muscle proteins found in the body.

SKELETAL MUSCLES

Skeletal muscles are bundles of muscle cells (also known as muscle fibers) embedded in connective tissue.  (Yu, T.Y., et al, 2017) These muscle proteins “are grouped into three general classifications: (1) myofibrillar, (2) stromal, and (3) sarcoplasmic. Each class of proteins differs as to the functional properties it contributes.”  (www.meatscience.org)

->  Myofibrillar Proteins

The first very important protein to take note off is the myofibrillar protein for the purpose of water binding and binding meat pieces together.  These muscle fibers are muscle cells, grouped into muscle bundles.  The structural backbone of the myofibrils is actin and myosin.  (Toldra, 2002) They are the most abundant proteins in muscle and are directly involved in the ability of muscle to contract and to relax.  (www.meatscience.org)  Myofibrils also include tropomyosin and troponin, regulatory proteins associated with muscle contraction.  Parallel to the long axis of the myofibril, are two very large proteins called titin and nebulin.  (Toldra, 2002)

Myosin is a protein which is described as the motor, and the structural protein, actin’s filaments are the tracks along which myosin moves, and ATP is the fuel that powers movement.  (Lodish, 2000)  Myosin “converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement.”  (Cooper.  2000)

“Together, actin and myosin make up about 55-60% of the total muscle protein of vertebrate skeletal muscle, with the thicker myosin myofilaments yielding about twice as much protein as the thinner actin myofilaments. Actin alone does not have binding properties, but in the presence of myosin, acto-myosin is formed, which enhances the binding effect of myosin.” (Patterson, The Salt Cured Pig)  In meat processing, it is important to note that it is the myofibrillar proteins which are soluble in high ionic strength buffers.  (Toldra, 2002)

“Texture, moisture retention, and tenderness of processed muscle foods are influenced by the functionality of myofibrillar protein.”  (Xiong, Y. L.;1994)  The pork muscle that contains the most myosin is the longissimus dorsi or the eye-muscle or longissimus muscle on the loin.  “The muscle fiber bundles of the longissimus dorsi are arranged at an acute angle to the vertebral column.  The cross-sectional area of the longissimus dorsi increases towards the posterior part of the ribcage, but it has an approximately constant cross-sectional area through the loin.”  (Animal Biosciences)

-> Sarcoplasmic Proteins

“The sarcoplasmic proteins include hemoglobin and myoglobin pigments and a wide variety of enzymes.  Pigments from hemoglobin and myoglobin help to contribute the red colour to muscle.” (www.meatscience.org)  These proteins are water soluble.  Besides myoglobin and hemoglobin, this class of proteins also includes metabolic enzymes (mitochondrial, lysosomal, microsomal, nucleus or free in the cytosol).  (Toldra, 2002)

Very important to remember for the purpose of meat processing is that myoglobin is the protein pigment responsible for the red colour in meat.  The redness of meat is largely dependant on the concentration of myoglobin.  Myoglobin is the storehouse for oxygen in the muscle.  Because different muscles need different oxygen levels, the concentration of myoglobin will differ between muscles.  The loin muscles in pigs are for example used for support and posture and therefore contains low levels of myoglobin.  Myoglobin levels are further influenced by species, breed, sex, age (older animals generally have more myoglobin), training or exercise (this is why free-range pigs have more myoglobin than stall-fed animals), and nutrition. (Pegg and Shahidi, 2000)

-> Stromal Proteins

“Connective tissue is composed of a watery substance into which is dispersed, a matrix of stromal- protein fibrils; these stromal proteins are collagen, elastin, and reticulin.

Collagen is the single most abundant protein found in the intact body of mammalian species, being present in horns, hooves, bone, skin, tendons, ligaments, fascia, cartilage and muscle. Collagen is a unique and specialised protein which serves a variety of functions. The primary functions of collagen are to provide strength and support and to help form an impervious membrane (as in skin). In meat, collagen is a major factor influencing the tenderness of the muscle after cooking.  Collagen is not broken down easily by cooking except with moist—heat cookery methods. Collagen is white, thin and transparent. Microscopically, it appears in a coiled formation which softens and contracts to a short, thick mass when it is heated and helping give cooked meat a plump appearance. Collagen itself is tough; however, heating (to the appropriate temperature) converts collagen to gelatin which is tender.  In the consideration of a TG mix, collagen is one of our most important considerations.

Elastin (often yellow in colour) is found in the walls of the circulatory system as well as in connective tissues throughout the animal body and provide elasticity to those tissues.  Reticulin is present in much smaller amounts than either collagen or elastin. It is speculated that reticulin may be a precursor to either collagen and/or elastin as it is more prevalent in younger animals.”  (www.meatscience.org)

It is interesting that collagen has been used for centuries to create strings to bind things and for strings on musical instruments.  Catstring or catgut is made by twisting together strands of purified collagen taken from the serosal or submucosal layer of the small intestine of healthy ruminants (cattle, sheep, goats) or from beef tendon and has been in use for a long time 900’s AD.  (Wray, 2006)  Gut strings were being used as medical sutures as early as the 3rd century AD as Galen, a prominent Greek physician from the Roman Empire, is known to have used them.   (Nutton, 2012)

Abū al-Qāsim Khalaf ibn al-‘Abbās al-Zahrāwī al-Ansari (Hamarneh, et al., 1963)(Arabic: أبو القاسم خلف بن العباس الزهراوي‎;‎ 936–1013), popularly known as Al-Zahrawi (الزهراوي), Latinised as Abulcasis (from Arabic Abū al-Qāsim), was an Arab Muslim physician, surgeon and chemist who lived in Al-Andalus in the early 900’s CE. He is considered as the greatest surgeon of the Middle Ages (Meri, 2005), and has been described as the father of surgery.  (Krebs, 2004).  He became the first person to have used Catgut to stitch up a wound. He discovered the natural dissolvability of the Catgut when his monkey ate the strings of his musical instrument called an Oud. (Rooney, 2009)

Later, in 1818, the modern founder of surgery, Joseph Lister, and his former student William Macewen independently and quite remarkably, almost at the exact same time, reported on the advantages of a biodegradable stitch using “catgut”, prepared from the small intestine of a sheep.  Over the ensuing years, countless innovations have extended the reach of collagen in the engineering and repair of soft tissue in medicine and numerous other industrial applications. (Chattopadhyay, 2014)  The interesting point should not escape our notice that collagen is included in our TG mixes ta facilitate meat protein – TG – connective tissue – TG – meat protein binding structure.  Collagen is surface-active and is capable of penetrating a lipid-free interface.  (Chattopadhyay, 2014)

The other major constituent of meat is, of course, lipids or fat but I deal with this separately below.

During thermal processing, moisture loss will take place.  Let us predict the optimal temperature range that will give us the right moisture loss and colour development in the shortest possible time.  Countries such as Australia sell their bacon cooked but in the UK, New Zealand, Canada, the USA and South Africa, bacon is sold par-cooked.  I, therefore, consider temperatures which will be considered par-cooked and fully cooked.

DIFFERENCES IN MOISTURE LOSS

“Bendall and Restall (1983) systematically studied the physical changes occurring during heating of intact beef-derived single muscle cells, and also the very small myofiber bundles of 0.19 mm in diameter (containing 40 to 50 cells) at final temperatures between 40 and 90 °C. In addition, the authors also studied heating of larger bundles of 2 mm in diameter.”  (Yu, T.Y., et al, 2017)

According to their work, the stewing process progresses as follows:

From 40 to 52.5 °C

Denaturation of sarcoplasmic (include hemoglobin and myoglobin) and myofibrillar proteins occurs.  Related to colour development the denaturation will effect sarcoplasmic protein even though its denaturation probably occurs from at least 25 °C.   Related to moisture and the range of 40 to 52.5 °C, a slow loss of fluid from the myofibers into the extra-myofiber spaces occurs without shortening. (Yu, T.Y., et al, 2017)  The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity. (Ceresinoa, 2018)

Between 52.5 and 60 °C

At this temperature, there is “an increasingly rapid loss of fluid from the myofibers, reaching a maximum rate and extent at about 59 °C.”  There is no overall shortening at this temperature mainly due to heat shrinkage of the basement membrane collagen (type IV and perhaps type V as well) at about 58 °C.   (Yu, T.Y., et al, 2017)

Between 64 to 94 °C

Considerable overall shortening and a decrease in cross-sectional area are noted, accompanied by increased cooking loss with heat shrinkage of the endomysial, perimysial, and epimysial collagen.”  (Yu, T.Y., et al, 2017)

Long Stewing

“Long periods of stewing causes partial or complete gelatinization of the epimysial collagen, followed by the peri- and endomysial collagen, resulting in the soft and tender feature of stews (Bendall and Restall 1983). It is worth mentioning that meat with a high pH (Zhang and others 2005) or fat content (Wood and others 1986; Jung and others 2016) has been shown to exhibit higher water-holding capacity.”  (Yu, T.Y., et al, 2017)

The important aspect for us is the key temperature of < 52.5 where moisture loss becomes “rapid”.  This gives us an important upper “meat temperature” limit above which rapid moisture loss occurs.

The following section confirms the conclusion of par-cooked bacon’s optimal thermal processing range of between 40 and 52 deg C.  Due to inconsistencies in the smoke chamber, it is suggested that a maximum internal core temperature of 40 deg C is set.

KINETICS OF THERMAL DENATURATION

Kajitani, et al, (2011) studied the kinetics of thermal denaturation of protein in cured pork meat related to each of the three protein classes of meat proteins namely myosin (from myofibrillar proteins), sarcoplasmic proteins and collagen (from stromal proteins).  Of great interest to us is the sarcoplasmic proteins which include the pigment containing myoglobin.

The first important consideration is that the “thermal denaturation of muscle proteins such as myosin, sarcoplasmic proteins and collagen, and actin, occurs at different temperatures. To describe those reactions during thermal processing, temperature dependency of the reaction rate constant is necessary.”  As the level of NaCl in the meat increased, “the thermal-denaturation rate constant of each protein increased.” (Kajitani, et al, 2011)

Adding salt to the sarcoplasmic proteins means that it starts to denature at a temperature of around 50 deg C, reaching a peak at around 68 deg C.  Adding Sodium Chloride moves the graph to the left.

heat.png

Graph source:  (Kajitani, et al, 2011)

Having now considered thermal treatment and smoke in some detail, we can move to a consideration of TG in particular, but we will broadly keep looking at colour development, binding strength, and water loss.

TG is mixed into solution before added to the meat.  The TG mix contains connective proteins and the first important matter to take into account is the solubility of these proteins.

The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity.  Optimal pH for commercial TG was found to be between pH 5.5 and 6.0. (Ceresinoa, 2018)

DIFFERENCES IN SOLUBILITY

In terms of the use of Transglutaminase, different proteins are used in the TG mix as added connective protein to enhance the overall binding action.  When TG is mixed in a solvent before application, different solvents will provide different solubility which may concern operators.

For example, TG containing stromal proteins such as collagen which shows low solubility in a neutral aqueous solvent such as water but high solubility in a curing brine solution with phosphates and salts on account of the high ionic charge of this solution.

Skeletal proteins.png

From Yu, T.Y., et al, 2017.

The solubility of different proteins under various ionic strengths further informs us of the importance of salt and phosphates in solubilizing myofibril protein.  Mixing the TG into a small brine solution has in my experience the best results.

MIXING AND TUMBLING – COLOUR LOSS AND BINDING

The system I developed over the years and used with great effect is to mix a batch of “stuffing meat” which I use in conjunction with whole muscles.  Whether such a mix is made or comminuted muscle meat prepared for sausages, researchers have found that mixing time has an effect on the color and will increase the deterioration of the desired color if conducted in excess of 12 min” (Sun, 2009).  Over the years I noticed a similar colour change if whole meat muscles have been over-tumbles, but if the meat is smoked, the colour change is immaterial.

The greatest benefit of the system relates to binding.  The reason why I use “stuffing meat” is that this combines modern binding systems such as transglutaminase with old-school meat processing techniques, such as chunking, flaking and tearing.  Bhaskar Reddy, et al. describes chunking and its benefits as “passing the meat through a coarse grinder plate leading to decrease in the particle size not greater than one and a half inch cubes.  This technique increases the surface for the extraction of myosin and aids in better binding during mixing.” (Bhaskar Reddy, et al.; 2015)  This describes the system I currently use to produce the stuffing meat.  Bhaskar and his colleagues refer to flaking and say that “high-speed dicing or slicing machine is being used for flaking and reforming of restructured meat products. Fine flakes produce more acceptable appearance, increase tenderness and decrease shear force value”, referencing Mandal et al., 2011Reddy et al., 2015.  They add another category which they refer to as  “sectioned and formed meats” which are “primarily composed of intact muscle or section of muscle that are bound together to form a single piece”, quoting Pearson and Gillet, 1996Mandal et al., 2011Sharma et al., 2013.  This is the process then of taking the whole muscle meat and joining them together in the grid system.  My method combines then chunking with sectioned and formed meats.

The “old school” method relies on the combined effects of salt, phosphate and mechanical action.  Bhaskar Reddy, et al. (2015) references Boles and Shand, 1998 who found that “by using this technology, the product must be sold either precooked or frozen because the product binding is not very high in the raw state but high yields (25% above meat weight) are possible.

One of the benefits of the “old school” methods is the effect of meat particle size. “An increase in meat surface area and an increase in the availability of myofibrillar proteins for binding is the net consequence of comminution.” (Sun, 2009).

“In a study to evaluate mixing time on the binding effect of restructured meat, Booren, Mandigo, Olson, and Jones (1982) found that there was a significant linear increase in binding strengths up to 12 min of mixing at 28C.”  (Sun, 2009)

The excellent review article of Sun (2009) makes reference to a study by Ghavimi,
Rogers, Althen, and Ammerman (1986) where they assessed vacuum, non-vacuum, and nitrogen back flush processing conditions at 1–38C during tumbling of restructured cured beef.  Fascinatingly, they concluded that meat had higher cooked yields in a non-vacuum atmosphere. This, in the context of the application of Transglutaminase, is a very interesting observation.

I have long proposed a re-examination of the viability of vacuum tumbling, but I recognise the entrenched nature of this technology in modern meat processing plants and propose a new line set-up for investigation.

Injector -> vacuum tumbler -> 24 hours resting station -> add TG -> ribbon/ paddle mixer -> filling station -> smoking/ cooking -> de-gritting -> freezing – slicing -> packing.

This eliminates the re-routing of meat back to the tumblers which are expensive assets while it achieves the application of the TG, final pick-up of any brine that purged out of the meat during resting as well as the balancing brine added after injection.  In order to facilitate a proper pick up of this “loose brine”, some processors choose to add between 1 and 2% pork protein at this stage which will mean that the brine added during this step consists of the pork protein and the TG blend in a small amount of brine.

Lets first look at why a tumbler works.  The interaction of the meat, rubbing against the meat and the pressure created as the mass of meat falls to the bottom of the tumbler during the drum rotation causes pressure which then “activates” the protein by causing the highly swollen muscular protein cells to burst.  Bhaskar Reddy, et al., (2015) quotes Feiner, 2006 who stated that it is the “kinetic energy released during falling of meat pieces at bottom of the tumbler which serves to disrupt cellular membranes, which in turn causes protein extraction.  It is the baffles inside the tumbler which “move the injected pieces of meat up the wall of the tumbler and once the pieces of meat reach a certain height, gravity causes them to fall.”  (Bhaskar Reddy, et al., 2015)

This is, in my opinion far more aggressively and successfully achieved through a paddle mixer or a ribbon mixer than only the falling of the meat inside the tumbler.  Mixing in a paddle or ribbon mixer will, in my estimation, better develop the myosin protein to become “sticky.”  Remember that the aim of this step is to “solubilize the protein, creating a layer of activated protein on the surface of meat which is responsible for slice coherency in the cooked product.  The sarcolemma surrounding the tightly swollen muscle cells is, in my opinion, more likely to be destroyed by the impact of energy from paddles than only tumbling and myofibrillar proteins will be released and solubilized (which is the object of tumbling).  There is considerable academic and anecdotal support for this.  Dikeman and Devine state in their Encyclopedia of Meat science, second edition (2014), commenting on the fact that paddle mixers run at reduced revolutions per minute (rpm), that they “can be useful for applying mecahnical action to whole muscle pieces. . .  to produce a surface protein exudate without damaging muscle integrity.”  (Dikeman and Devine, 2014:  126, 127)

Meat must be mixed until they become tacky – almost furry.   “Rust and Olson (1973) found that the extraction of myofibrillar proteins on the surface of meat has two functions. One is to act as a bonding agent holding the meat surfaces together and the other is to act as a sealer when thermally processed and therefore, aid in the retention of water in the muscle tissue.”  “In addition, cellular disruption of the meat tissue occurs during tumbling which together with the curing additives allows the meat to improve the yield (Chow et al., 1986). Constraining connective tissue sheaths around muscle fibres are disrupted, allowing further myofibrillar swelling introduced by salt (Katsaras and Budras, 1993).  (Bhaskar Reddy, et al., 2015)

It is, of course, possible to mix the TG mix into the stuffing meat by hand, but one loses all the benefits listed above.  For the exact reason, I believe a more aggressive treatment of the whole muscle meat just prior to filling into the grids should yield far better reshaping and binding results.  Too little mixing will result in meat being “loose” and a failure to bind together.  Too much mixing, on the other hand, will result in a loss of tenderness and the product being “rubbery”.  (Pearson and Gillett, 1999)

The reason why mixing is essentially done in a tumbler under vacuum is mainly that, removing the oxygen, prevents oxidation.  This prevention of oxidation will, however, also be accomplished by maintaining a low temperature during mixing which is obviously also very good to control negative mirco-growth.  (Pearson and Gillett, 1999)

Bhaskar Reddy and colleagues state that tumbling or massaging (physical action upon the meat, in whatever form) “improves the speed of curing by increasing salt absorption.”  (Bhaskar Reddy, et al., 2015)  It is this reason why I still prefer the two-step tumbling.  The solubilization of the proteins by the fat and the phosphates are greatly enhanced if the meat is left to rest for 12 or 24 hours and re-tumbled/ mixed which of course will increase the protein bind.

Having made this statement, we get to a long-standing debate related to tumbling namely if one must tumble continually (uninterrupted) or if one must have intervals of rest periods.  For every study that intermitted tumbling is superior, there seems to be a study that shows continues tumbling is superior.  Why is the one preferred over the other?  Exactly because brine needs time to diffuse into the muscle.  (Krause et al., 1978)  One needs the drum to stop turning so that the meat can be immersed in the brine in order to absorb into it.  This is not achieved, as many believe, by the vacuum which presumably opens up the meat fibers and somehow pulls the brine into the meat.  The reason why this is done intermittently (tumble, rest, tumble, rest) and not in a two-step process of tumbling, unloading, resting in the chiller, loading into the tumbler and tumbled again, is presumably to eliminate the need to load and unload the tumbler twice.  In a high throughput factory, this should, in any event, be done with loading equipment and should not be a consideration.  I also doubt if the total time of resting in a tumbling program will be sufficient for the brine to be absorbed if one takes absorption rates into meat into account.

Whichever way I look at it, a two tumbling system is preferred over injection, resting, tumble, adding TG 15 minutes before the end of the program and grid filling (only one tumbling step).  There are simply too many advantages which are ignored which one will get in a system of injection, tumbling, resting, TG tumble, grid filling.

My only concern of using paddle mixers for the second step and not tumblers relates to the formation of foam.  If foam is created, this may lead to protein denaturation and the binding strength will be compromised (Kerry et al., 2002)  This will have to be evaluated.  In my own experience, when using a blender to do the stuffing meat, this has never in 2 years of using the technique created foam.  Whole muscles will have to be tested for foam formation which I know happens in a tumbler if only a partial vacuum is pulled.  I suspect the paddle mixer will work very well.

DIFFERENT GELLING ABILITY OF DIFFERENT PORK MUSCLES

A matter of interest is the different gelling strengths of different proteins.  Between poultry, beef, fish, milk, and pork, but also between different pork muscle groups.  This is of interest to me for choosing the best muscle to produce the stuffing meat.  Robe and Xiong (1993) reports that pork longissimus dorsi muscles (predominantly white) formed stronger gels when compared to pork serratus ventralis muscles (predominantly red).

One would not use the longissimus dorsi muscles to produce stuffing meat, but there may be muscle groups in the leg with similar visual characteristics.  Is there an advantage in using some of these muscle groups for the stuffing meat?  It is an interesting question that must be investigated.  Robe and Xiong (1993) concluded that their work indicates that “red and white muscle types (in pork) should undergo different processing treatments for optimum quality meat products.”

PRESSURE – COLOUR AND BINDING

Contrary to popular belief, pressing of the meat does not facilitate the binding or the effect of TG in any way.  (Pearson, and Gillett, 1999)  Pressing into moulds have a few important functions.  In the first place, it ensures the meat, particularly large meat pieces, are forced into a regular shape which is the key behind improved slicing yields.

The second reason for pressing relates to surface area and meat contact.  If there are cavities in the meat log, binding at those locations will obviously be compromised and the appearance of the meat slices, especially when bacon is sliced, will be undesirable.

SALT – COLOUR AND BINDING

Sun (2009) points out that “discoloration of restructured steaks can be caused by salt. A decrease in color desirability with increased salt levels has been observed by some researchers (Huffman & Cordray, 1979; Schwartz & Mandigo, 1976). The raw color could be improved by sodium tripolyphosphate (STP), which helps to compensate for the effect of salt (Schwartz & Mandigo, 1976).  As a matter of interest, Huffman, Ly, and Cordray (1981b) as cited by Sun, “showed that addition of salt at all levels increased thiobarbituric acid (TBA) values and decreased color levels.”  No such effect has however been noticed with heat treated, smoked and cured meat.

Salt and phosphates during the mixing/ tumbling step are essential in that it aids the extraction of myofibrillar proteins which in turn aids in the overall binding.  (Pearson and Gillett, 1999)

The interaction of salt and TG is a key consideration.  Sun reports that “in cooked restructured meat products, gel firmness and water-holding capacity (WHC) have been reported to increase by the addition of TG in high-salt (2%) products but not in low-salt products (Pietrasik & Li-Chan, 2002b). TG was able to improve consistency (firmness) but not cooking loss of the product in a low salt (1%) system (Dimitrakopoulou, Ambrosiadis, Zetou, & Bloukas, 2005).”  (Sun, 2009)

“Kuraishi et al. (1997) investigated the effect of salt on binding strength and indicated that provided there was addition of salt (NaCl), TG treatment caused effective binding of meat pieces. Their result showed that an increase in binding strength caused by adding salt (1.0–3.0%) with TG when compared to TG alone.”  (Sun, 2009)

PHOSPHATES – BINDING

Phosphate generally enhances the effect of salt.  Sun (2009) reports that “a variety of phosphates in different combinations, concentrations, and with concomitant salt concentrations were evaluated by Trout and Schmidt (1984). They found that tetrasodium pyrophosphate had the greatest binding effectiveness, which was followed by sodium tetrapolyphosphate, and then sodium hexametaphosphate.

They concluded that most of the changes in binding could be explained by the ionic concentration of the phosphates. STP also delays development of rancidity and is added at a level of about 0.25% for adequate protein extraction and flavor development (Pearson & Gillett, 1996). Nielsen, Peterson, and Møller (1995) observed optimum effects of STP on the texture at a concentration of 0.2%. (Sun, 2009)

COMBINATION OF STROMAL PROTEINS WITH ALGIN/ CALCIUM OR TG

I include this in a separate heading, due to the low-cost stromal proteins of collagen, elastin, and reticulin and muscles with a high percentage of it.  The protein is of huge interest in TG formulations.  How will the inclusion of pork gelatin aid the binding system with TG?

In considering connective tissues, it is astounding to recognise the monumental presence of K. B. Lehmann.  In terms of the curing reaction in meat, it was this German hygienist and bacteriologist from the Hygienic Institute at Würzburg, Germany who confirmed Polenski’s suspicions (Saltpeter) that nitrite is the key in the cured colour formation and not nitrate as was believed.  He further importantly identified its colour spectrum when diluted in alcohol.  (Fathers of Meat Curing)  It was probably based on his work and that of his student, Karl Kißkalt, that the German government allowed the use of nitrite in curing brines during the first world war.

It was Lehmann and his coworkers who showed that “the toughness of different cuts of meat, measured mechanically, was closely related to their content of connective tissue, and that the decrease in toughness resulting from cooking was related to the collagen of connective tissue rather than to the elastin.”  (Mitchell, et al.; 1926)

They found that “under the influence of moist heat the collagen is readily changed to gelatin, thus losing its toughness. In the raw condition, white fibrous connective tissue (mainly collagen) is almost twice as tough as yellow elastic connective tissue (mainly elastin), but when cooked, the former loses most of its toughness while the latter remains practically unchanged in this respect.”  (Mitchell, et al.; 1926)

“Ensor, Sofos, and Schmidt (1990) concluded that the use of high-connective-tissue meat or addition of concentrated forms of connective tissue in algin/calcium gel restructured meats could improve product texture and reduce formulation costs.”  (Sun, 2009)  Gelatin is the ideal thickening agent to accompany transglutaminase since it contains a variety of different amino acids, including our old friends Glutamine and Lysine which are now cross-linked by the action of transglutaminase.  (Aguilar, M. R. and Román, J. S.; 2014:  186)  It is important to use the right kind of gelatin.  Fish and pork gelatin will be objectionable for either religious or allergen concerns by various processors in various parts of the world and it is an important consideration.

I am aware of tests underway in Chili where pork protein is tested in conjunction with TG to replace MDM.  The viability of this must be tested.

WHAT ABOUT FAT?

We skipped over fat when we looked at the constituents of muscles and now returns to it.  Many people refer to fat as lipids, but fats are only a subgroup of lipids called triglycerides.  Lets set some basic concepts up, to begin with.  Human body fat, animal, and vegetable fats have triglycerides as its main constituent.  Their function in blood is to facilitate bidirectional transference of adipose fat which is the fat layer under our skin, around internal organs), in bone marrow, intermuscular and in the breast tissue.  

Let’s look closer at the adipose tissue.  It is “composed of a loose collection of specialized cells, called adipocytes, embedded in a mesh of collagen fibers.  We looked briefly at collagen when we reviewed the stromal proteins.  The main role of adipose tissue in the body is its role as a fuel tank for the storage of lipids and triglycerides.

One gets white and brown adipose tissue with white tissue being the most numerous.  “The main role, or function, of white adipose tissue is to collect, store and then release lipids.  However, because of the properties of the lipids being stored, the adipose tissue also acts as a protective cushion (resists knocks) and also as a layer of insulation against excessive heat loss.

Lipids conduct heat very poorly (only about a third of the rate of other materials) so even a small layer of adipose cells (about 2 mm) will keep a person warm at 15 degrees centigrade, whereas a person with only a 1 mm layer of protection will be feeling quite uncomfortable.

About 80% of average white adipose tissue is lipid, and of that, about 90% is made up of the six triglycerides: stearic, oleic, linoleic, palmitic, palmitoleic and myristic acid.  Also stored are free fatty acids, cholesterol, mono- and di-glycerides.”  (brooklyn.cuny.edu)

“Each adipocyte cell has a large, central, uniform, lipid packed central vacuole which, as it enlarges, pushes all the cytoplasm, the nucleus, and all the other organelles to the edge of the cell, making it look a bit like a band or ring under the microscope.

These cells can vary in size from about 30 microns to over 230 microns, and, despite their distorted appearance, contain all the necessary biochemical machinery of other cells.

Every adipose cell must touch at least one capillary or blood vessel (an artery or vein).  From this the cells draw all their needed supplies, including lipids.

Fatty foods, with high lipid content, often provide more lipids than can be digested and used right away.  The excess is stored in the adipose tissue.  Excess carbohydrate and protein taken in with meals can also be converted to fat (usually in the liver) and then moved to the adipose tissue for longer-term storage.

Lipids are the major fuel reserve for humans and most mammals.  These molecules are very efficient at storing needed energy.  One gram of fat stores about 9 kcal per gram, compared to carbohydrate or protein (4 kcal per gram).  For mobile animals, this means that less bulk has to be carried around and a normal sized body that is about 20% fat has enough stored energy to last about 20 – 30 days without eating!”  (brooklyn.cuny.edu)

Let’s look more closely at triglyceride.  There are many types of triglycerides.  We are all familiar with the two main groups of triglycerides, namely saturated and unsaturated types. Saturated fats are “saturated” with hydrogen — all available places where hydrogen atoms could be bonded to carbon atoms are occupied. the importance to us for meat processing is its melting point which is higher and are more likely to be solid at room temperature.  It is this saturated fats that, when ingested, raises the level of cholesterol in your blood.  (daa.asn.au)

On the other hand are the unsaturated fats which have double bonds between some of the carbon atoms, reducing the number of places where hydrogen atoms can bond to carbon atoms. For our purposes, the net result is that they have a lower melting point and are more likely to be liquid at room temperature.  These fats help reduce the risk of high blood cholesterol levels and have other health benefits when they replace saturated fats in the diet. (daa.asn.au)

When one works with pork fat, it is important to keep an eye on the temperature.  During processing, highly unsaturated fats will start to melt and form a fat coating on the product which is visually unappealing. (Toldra, 2010)  Beef fat is firmer with a more intense flavour in comparison with pork or chicken.  Beef fat’s melting point is comparable to pork kidney fat due to the low content of collagen and saturated fats.  The reason why pork fat is popular is that it is largely tasteless and flavourless.  The rules for making meat emulsions are based on fat choice and temperature. “Pork backfat gives the best suitable product for slicing.  Jowl and belly fat can also be used.  The endpoint chopping temperature should remain below 18 deg C, 12 deg C, and 8 deg C for beef, pork, and poultry fat respectively to avoid fat melting.”  (Toldra, 2010)

“To make spreadable products fat must be dispersed in the liquid state at “hot” temperatures.  The endpoint chopping temperatures should be above the fat melting point (i.e., 35 deg C).  To achieve this final temperature, fat is usually pouched in water at temperatures above 80 deg C before being mixed with protein (liver or lean meat).  The object is to reach a final internal temperature between 50 and 60 deg C for ham fat and between 70 and 75 deg C for jowl fat.  Fat poaching also causes contraction of the connective tissue which will facilitate the grinding; it eliminates low melting fats, which can cause weight losses during cooking and it lowers the microbial content.  Thus, for hot emulsions, low melting fat is preferred such as ham and jowl fat remain firm during cooking at high temperatures.”  (Toldra, 2010)

Triglycerides are composed of three fatty acids.  The fatty acid content in animals depends on age, type of feed and the environment.  Diet plays an important role, especially in pork which is one of the reasons why pork, raised in informal settlement environments are very poor substitutes for commercially farmed animals where feed are strictly controlled.   The properties of the fat will generally be determined by the composition of the fatty acids.  “It will be soft (oily appearance) and prone to oxidation when there is a high percentage of polyunsaturated fatty acid linoleic (typical of feed rich in corn, for instance) and linolenic acids.”  (Toldra, 2002)

There are two main groups of lipids in the body.  The one is triglycerides which we just had a look at.  The other is phospholipids.  They are present in very small amounts but have a strong key role in flavour development and the oxidation of postmortem meat.  They also have a relatively high proportion of polyunsaturated fatty acids in comparison to neutral lipids.  Some of the major constituents are phosphatidylcholine (lecithin) and phosphatidylethanolamine.  Phospholipids vary depending on the genetic type of the animal and anatomical location of the muscle.  Therefore, the amount of phospholipids tends to be higher in red oxidative muscles than in white glycolytic muscles.  (Toldra, 2002)

The interaction of fat and protein is a very important consideration in restructuring meat. “The fat level clearly influenced the structure of the gel/ emulsion network, as reflected by the differences in the type of protein molecular interactions involved in its formation, and this, in turn, affected the fat binding properties and the texture of the end product.” (Sun, 2009)

It is difficult to bind fat effectively to meat.  De NG, Toledo, and Lillard (1981) found that water and fat binding by meat batters diminish when temperatures exceed 16°C during comminution.  This speaks directly to the preparation of stuffing meat and it requires for the meat temperature to be kept as low as possible, but not so low that it makes it impossible for workers to use it in the restructuring process.

Secondly, when one talks about fat and stuffing meat, one must consider the interaction between a TG blend containing pork gelatin and fat in the meat mix which is less than optimal.  TG by itself is not a good binder for fat.  The easiest way of handling fat in stuffing meat is to avoid it.  I have found pork fillet to be particularly suited due to its lean nature.

Remember that gelatin “works by creating a very fine mesh of proteins, between which the (hydrophilic) liquid gets trapped.  A mixture of fat and water isn’t a liquid. It can be either a rough two-phase mixture, with visible fat droplets swimming around in the water, or it can be an emulsion, with invisibly small fat droplets dispersed through the water. Emulsions appear smooth, e.g. milk.”  (cooking.stackexchange.com)  Fat in the stuffing meat will interfere with the binding.

As far as the whole meat muscles are concerned, it is important to lay the meat pieces fat down in the mold to minimize contact between added meat and fat.

FREEZING/ CHILLING

After thermal treatment, the meat must be frozen as soon as possible.

Sun (2009) reports that “although most of the studies using TG for restructuring meat conducted by incubation meat at optimum temperature (37–508C) of MTG or by cooking to obtain sufficient binding strength, some researchers obtained good binding effect by using cold binding (2–58C), with the combination of TG and sodium caseinate, without addition of salt or cooking (Kuraishi et al., 1997; Serrano, Cofrades & Jimenez Colmenero, 2004). Kuraishi et al. (1997) indicated that the TG reaction condition of 58C for 2 h would not enable any bacteria present to increase much and discoloration of the meat was not observed in the raw, refrigerated state. In my experience, IT binds very well at lower temperatures.

The maximum activity observed for TG was at 40 °C for the commercial TG. At temperatures above 45 °C, TG suffered a rapid drop in its activity.  Optimal pH for commercial TG was found to be between pH 5.5 and 6.0. (Ceresinoa, 2018)

DIFFERENT BACTERIA PRODUCE TG WITH DIFFERENT PROPERTIES

It has been found that different strains of bacteria that produce the enzyme TG, produce it with different yield and properties.  Different TG producing bacteria strains are still being identified from different environments. “The isolation of a strain of Streptomyces mobaraense was the first step towards the extensive commercial exploitation of this enzyme. Thereafter, a number of various microbial strains, such as Streptomyces lydicus, Streptomyces cinnamoneum CBS 683.68, Streptomyces sp. CBMAI 837, have been found being able to biosynthesize TG extracellularly.  How the TG is produced definitely impacts its application.  TG’s of various origins and in different concentrations have different functionality.  (Ceresinoa, 2018)

Generally, increased TG concentration produces a better binding of meat.  The optimum pH for the commercial TG was found to be between pH 5.5 and 6.0, but TG from different strains have a different optimal pH.  TG from Bacillus circulans BL32, for example, has been reported to have an optimal pH of 7.2.  (Ceresinoa, 2018)

“As to temperature influence on TG activity, minor differences were seen between the enzymes, with a maximum activity observed at 40 °C for the commercial TG and at 35–40 °C for SB6. At temperatures above 45 °C, both enzymes suffered a rapid drop in their activities.  These findings are consistent with studies of TG derived from other streptomycetes such as Streptomyces hygroscopicus and Streptomyces sp. CBMAI 837. (Ceresinoa, 2018)

DEBONING

Sinew and excess fat must be removed in the trimming stage to maintain product quality and consistency.  The use of a grid system allows the deboning department to trim to exact product specifications.  In regular bacon production, leaving the silverskin and membrane on the meat is advisable since it will prevent excess moisture loss during thermal processing.  In a restructuring scenario, it will have to be removed during trimming because it will interfere with the binding.

WHAT ABOUT PSE MEAT?

PSE pork meat is a scourge in the Western Cape during the summer and using TG does not resolve PSE.  An excellent article on an evaluation of factors impacting on meat quality in relation to PSE is Differentiation of pork longissimus dorsi muscle regarding the variation in water holding capacity and correlated traits.

It is possible to address PSE.  The first option will be so source meat during the summer from non-Western Cape sources, but this presents difficulty for the farmers who are the backbone of the industry and may go against strategic alliances.  A second strategy will be to work closely with farmers and the local abattoirs because much can be done pre and immediate post slaughtering.  These are, however matters that are notoriously difficult to implement.

What can be done from a processing perspective? Motzer, Carpenter, Reynolds, and Lyon (1998) successfully used pale, soft and exudative pork to manufacture restructured hams.  The problem with producing bacon from PSE meat is that “due to the rapid pH drop while muscle temperature remains high, the proteins in the myofibrillar fraction become partially denatured and lose their functionality.  Denaturation of myosin in PSE muscle ultimately affects the water holding capabilities of the meat system. As a consequence, products manufactured with PSE may be expected to lose higher amounts of water.”  (Motzer, et al., 2006)  The unfortunate reality is that 100% PSE meat cannot be utilized in high quality processed products (Marriott, et al. 2006).

Motzer and coworkers (2006) report on Shand et al. (1994) who evaluated the effects of various levels of salt, temperature and kappa carrageenan on the bind of structured beef rolls and reported that as salt or levels of kappa carrageenan increased, the bind increased.  They found that kappa carrageenan was the only binder different that when adequately solubilized improved adhesion of PSE meat.

As far as water holding capacity, they found that adding modified food starch (MFS) and isolated soy protein (ISP), enhanced the water holding capacity of hams produced from PSE pork meat.  They noted that isolated soy protein (ISP) “resulted in a thicker adhesion than normal for the meat pieces. Manual stuffing became difficult and often resulted in air pockets within the meat log.”  (Motzer, et al., 2006)  This will, however, be overcome by a proper press system.

Even though there were improvements in the ham, the fact remained that “due to loss of structural integrity, PSE meat will lose considerable water “, especially after thermal processing.  Most of the water is released due to the partially denatured myofibrillar proteins.”  (Motzer, et al., 2006)

The complete article can be found at PSE Meat Treatment.  Without reformulating a brine for the summer in Cape Town, incorporating kappa carrageenan, MFS, and ISP, losses in bacon production will remain material for pork procured locally.  It will manifest in excessive purge in the final product stage, excessive moisture loss during and after thermal processing and poor binding of restructured parts of the bacon logs.

Of course, a strategy will be to produce ham with the badly affected meat.  “Motzer et al. (1998) revealed that utilizing 50% PSE pork in a restructured product with either modified food starch or carrageenan yielded better quality pork than 100% PSE treatments.  Schilling et al. (2002) later demonstrated that combining 25% PSE and 75% RFN (red, firm, and non-exudative) pork in a chunked and formed ham was similar in quality to a 100% RFN pork sample when soy protein concentrate and modified food starch were incorporated together at 2 and 1.5%, respectively. Similarly, Torley et al., (2000) reported that increasing the ionic strength and utilization of polyphosphates resulted in increased cooking yield similar to that of a product manufactured from RFN pork.”  (Marriott, et al. 2006)

It is my suggestion that all these be tested in a summer mix of products to compensate for the extraordinary level of PSE prevalent in regions like the Western Cape during the summer.  “This research makes it clear that PSE pork can be incorporated into processed products, but it can be unsatisfactory to use formulations with more than 25% PSE. Samples formulated with 25% PSE pork exhibit acceptable texture, but those formulated with 75 or 100% PSE often sustain cracking.”  (Marriott, et al. 2006)  This relates to cooked hams. Bacon is a different matter and mixing PSE and non-PSE meat cannot be part of the solution. Producing hams instead of bacon with such meat is an option.

The bottom line is that solutions exist and an effective strategy is possible but will require focus and cooperation.

INCLUSION OF OTHER PRODUCTS

I have for some time considered the inclusion of a  blood-based binding system with TG which “can be used for binding comminuted and large pieces of meat (Boles & Shand, 1998, 1999). The binding mechanism of restructured meats is based on the blood clotting action between fibrinogen, thrombin, and TG. Cross-linking and gelation between fibrin itself and between meat collagen and the fibrin are induced by TG (Sheard, 2002).”  (Sun, 2009).

Other products to consider for inclusion are crude myosin, extract, surimi (Chen, Huffman, & Egbert, 1992), egg white powder, raw egg white, egg powder, bovine, porcine, lamb, broiler plasma powders, broiler breast meat powder, gelatine (Lu & Chen, 1999), dried apples, corn crumbs, mushrooms (Marriott, Graham, Schaffer, & Boling, 1986c), rice bran oil and fiber (Kim, Godber, & Prinaywiwatkul, 2000), and walnut (Jime´nez Colmenero et al., 2003; Serrano et al., 2006).

CONCLUSION

TG represents one of the most exciting developments in meat processing from the perspective of the large-throughput meat factories.  The optimal utilization of the technology is still in its infancy, despite the many decades that passed since it was first made available from the shores of Japan.

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Concerning the direct addition of nitrite to curing brine

by Eben van Tonder

This article is available for download in pdf: Concerning the direct addition of nitrite to curing brines

See, Bacon & the Art of Living,

Chapter 11.03: The Direct Addition of Nitrites to Curing Brines – the Master Butcher from Prague

Chapter 11.04: The Direct Addition of Nitrites to Curing Brines – The Spoils of War

ebenvt bacon belly ebenvt Prague Powder

Introduction

Bacon and the art of living is a study in the birth of the elements of bacon curing.  Neither the chemical reactions, nor the different mechanical processes are simple.  Everything about bacon is complex and beautiful.  One of the most amazing stories within the grand story of bacon, is the story of sodium nitrite.

Pork is changed into bacon by the reaction of nirtrite (NO2-).  With salt, it is the curing agent.  The meat industry uses nitrite in the form of an ionic compound, sodium nitrite.  It is sold as Quick Cure or Insta’ Cure, Prague Salt, Prague Powder or simply Pink Salt or Curing Salt.  It is coloured pink to distinguish it from ordinary salt (sodium chloride).  Every spice company sells it.  It is the essential ingredient in the meat curing process.

Meat changes colour from the red fresh meat colour to an unappetising brown colour within days. (1)  If one injects nitrite into the meat or rubs a mixture of salt and a small percentage of nitrite onto it, the meat will develop an appatizing reddish/ pinkish fresh meat colour (Hoagland, Ralph.  1914) and a characteristic cured taste.  It will retain this colour for weeks and months if packed in the right conditions.  (1)  Nitrite provides an indispensable hurdle against a particularly nasty food pathogen, clostridium botulinum.  It also endows the meat with a distinct cured taste.

During ages past, it has however not been nitrite that was added to meat to accomplish this, but its cousin, nitrate (NO3-).  They may be cousins, but are very different in characteristics. Nitrate takes several weeks or even months to cure meat where nitrite accomplishes the same task in 12 hours.  How the change happened from using nitrate or salpeter in meat curing to nitrite is an epic story.

Overview

This article tracks the migration of the meat industry from the use of saltpeter (potassium or sodium nitrate) as curing agent to sodium nitrite.  It gives an overview of the scientific discoveries which started to reveal the mechanisms of meat curing.   This understanding lead to the realisation that a direct application of nitrite as the curing agent will be vastly superior to the use of saltpeter (nitrate).

This was a dramatic discovery since in the late 1800’s and early 1900’s, the world saw nitrite as a dangerous drug at best and a poison that polluted drinking water and cause death of cattle.  Using this directly in food and meat curing was unthinkable.

Sodium nitrite was available in this time for application in the coal-tar dye and medical industries.  Science and engineering have however not worked out its large scale production in a way that will make it a commercially viable proposition for direct use in meat curing from a price and availability perspective.

World War One provided the transition moments required to change everything.  Germany invested heavily in nitrogen related technology for the war.  The most organised scientific and engineering environment on the planet in the early 1900’s focused its full attention on overcoming the manufacturing challenges in the service of the manufacturing of munitions.  It also required this technology to overcome the challenge of being cut off, as a result of the war, from the natural sodium nitrate deposits in Chili that it required as fertilizer to drive its enormous agriculture sector during the war.  At the same time, the use of saltpeter in meat curing was prohibited under the leadership of Walther Rathenau so that the valuable nitrate could be reserved for manufacturing of munitions.

This prohibition, I believe, was the initial spark that caused butchers to change to the use of sodium nitrite.  At the same time, sodium nitrite was being produced in large volumes since it had, in its own right, application in the manufacturing of explosives.  Health concerns and probably the need to have it reserved for munitions, lead to a ban, similar to nitrate, on its use in meat curing.  So, World War One solved the scientific challenges of large scale manufacturing of sodium nitrite, the engineering challenges of building production facilities and provided the impetus for the meat industry to change by banning the use of saltpeter in meat curing.  The ban was lifted after the war.

Following the war, Germany had to find markets for its enormous war time chemical stock piles.  One of the ways it “sold” sodium nitrite was as a meat curing agent based on its inherent benefits of curing consistency and the vastly shorter curing time required.

It was introduced to the world mainly through the Chicago based firm, Griffith Laboratories, who imported it as Prague Salt from Germany and later improved on it by fusing the sodium nitrite to sodium chloride and sold it as Prague Powder.

Early humans to Polenski (1891)

Early humans did not know they added nitrate to the meat.  A mixture of salt and a small amount of saltpeter was used to cure meat in order to preserve it and to retain the fresh meat colour.

Saltpeter is found naturally around the world in typically dry areas.  Deposits exist in India, China, Mexico, the USA, and the Middle East.  Despite its wide occurrence, the concentration of natural saltpeter is low.  (Whittaker, CW, 1932: 10)

Saltpeter is also made by human effort.  Europe, particularly Germany and France, Great Britain, India and the United States all acquired the technology to produce satpeter.  (Van Cortlandt, P, 1776:  7, 8)

In South Africa, saltpeter deposits are found in the Griquatown beds of the Transvaal geological system.  It extends from just South of the Orange River Northwards to the Kalahari Desert and then Eastwards into the Old Transvaal from Zeerust to Polokwane. The nitrate deposits occur in the middle portions of these beds, in softer and more decomposed shale.  These South African reserves have fortunately never been mined even though it was used on a small scale to make gunpowder for the old Boer government.  (Whittaker, CW, 1932: 10)

Saltpeter was at the heart of the arms race of the middle ages.  It was used mainly in gunpowder, but as the worlds population grew, it became indispensable as a fertilizer and for curing meat. (See Bacon and the art of living, chapters 2, 3 and 4)

The French chemist, Antoine Lavoisier worked out its chemical composition.  It is an ionic compound consisting of the metal potassium and its power is nitrate.  Potassium Nitrate.  (Mauskopf, MSH.  1995:  96)  Trade in Saltpeter around the world was done through companies such as the Dutch East Indian Company (Dutch abbreviation, VOC) who traded it for its main use as an ingredient in gunpowder.  It was by volume one of the largest commodities traded by the Dutch East Indian Company who set up the trading post in 1652 that became Cape Town.  

Major developments shifted the balance of power away from Indie, China and home grown saltpeter production to South America where huge deposits of sodium nitrate were discovered that would become the principal source of the worlds nitrate for much of the 1800’s.

A man walks down a dirt road in the Atacama Desert. Despite being one of the most inhospitable places on earth, the Atacama is still mined: in 2010 this made world-wide news, when the Copiapó mining accident led to the dramatic rescue of 33 trapped miners (AP Photo/Dario Lopez-Mills).
A man walks down a dirt road in the Atacama Desert. Despite being one of the most inhospitable places on earth, the Atacama is still mined: in 2010 this made world-wide news, when the Copiapó mining accident led to the dramatic rescue of 33 trapped miners (AP Photo/Dario Lopez-Mills).

A popular legend tells the story of the discovery by two Indians in the Atacama desert in the South of Peru.  According to the legend, after a hard day’s work, they camped in the Pampa and started a campfire to warm themselves.  All of a sudden the ground started to burn and they ran away, thinking that they have seen the devil.  They reported the event later to a priest in Camina who returned to the site.  He had it analysed and found it to contain sodium nitrate (the same power as potassium nitrate, but linked to another common metal).  The priest, according to the story, threw the rest of the soil in the courtyard of his house and saw the plants grew vigorously.  He recommended the soil as an excellent tonic for the plant kingdom.  (Wisniak, J, et al., 2001 :433)

So was discovered the enormous sodium nitrate deposits of the Atacama desert. The fertilizer properties of the salt was known long before the 1600’s.   There are references to saltpeter and the nitrate ground in 1604.  During the time of the Spanish Conquest, in the 1700’s, miners working in the South of Peru realised that gunpowder could be manufactured from the material in the soil instead of potassium nitrate.  (Wisniak, J, et al., 2001 :433)

A report published in 1803 by Juan Egana, Secretary of the Royal Court of Mines in Chile showed the Huasco region is “covered in a large part by a crust of niter salt, well crystallized, and several inches thick” (Wisniak, J, et al., 2001 :434)

The region was developed and by 1850 exports reached 24 000 tons/ year.  In 1910 it was 2.4 million tons per year and by 1916, 3 million tons per year from 97 plants. (Wisniak, J, et al., 2001 :434)

By the beginning of the 1900’s the country buying the largest quantity of the Chilean saltpeter was Germany (Wisniak, J, et al., 2001 :434) who used it aggressively in their agriculture sector as fertilizer.

There is a close correlation between sodium and potassium nitrate.  Its difficult to distinguish between sodium and potassium nitrate just by tasting it.  Scientists were able to distinguish between the two compounds from the mid 1600’s and knew that sodium nitrate had a much greater ability to attract water (Whittaker, CW, 1932:  3).  This made sodium nitrate a much better curing agent than potassium nitrate.

Nitrite was described in 1864 by the English Physiologist, B. W. Richardson.  He outlined how to manufacture it and its chemical properties.  (Wells, D. A., 1865:  233)  Much earlier, in 1777 the prolific Swedish chemist Scheele, working in the laboratory of his pharmacy in the market town of Köping, made the first pure nitrite. (Scheele CW. 1777)   He heated potassium nitrate at red heat for half an hour and obtained what he recognized as a new “salt.” The two compounds (potassium nitrate and nitrite) were characterized by Péligot and the reaction established as 2KNO3→2KNO2+O2. (Péligot E. 1841: 2: 58–68) (Butler, A. R. and Feelisch, M.)

The technology existed in the 1800’s to not only produce potassium nitrate (salpeter) and nitrite, but to also test for these.

Remember that curing up till 1890 has been attributed to saltpeter (potassium nitrate) or Chilean saltpeter (sodium nitrate).  In 1891 a German food scientist, Dr Ed Polenski, working for the German Department of Health made an observation that would change the world while studying curing brines.  When he tested the curing brine made from saltpeter and salt, days after it was made, he found nitrite to be  present.  This was surprising since saltpeter is potassium or sodium nitrate, not nitrite.

Dr Ed speculated that the nitrate (NO3-) was changed into nitrite (NO2-) through bacterial action, a reduction step between nitrate and nitrite that was well understood by this time.  He had a hunch that nitrite is responsible for curing of meat and not the nitrate directly, as was previously thought.

From Polenski (1891) to WWI (1914 to 1918)

world war 1

Following Dr Ed’s observations in 1891, considerable resources from around the world were dedicated to understand the chemistry of meat curing.

When World War One broke out, the concept of nitrite as curing agent (as opposed to nitrate) was firmly established.

Ralph Hoagland, Senior Biochemist, Biochemie Division, Bureau of Animal Industry, United States Department of Agriculture, published an article in 1914, Coloring matter of raw and cooked salted meats.  In this article, he shows that nitrite as curing agent was a known and accepted fact by the outbreak of World War One (Hoagland, Ralph.  1914)

Readers who dont have an interest in the detailed description of the key discoveries may want to skip over the rest of this section altogether or glance over it generally.  The goal of the section is to give the reader a sense of how firmly and universally the concept of nitrite as the curing agent was established by 1914.  In the midst of the technical names and jargon, don’t lose the sense of the universal interest.  The 1700’s, 1800’s and beginning of the 1900’s was a time when the average person was as interested in chemistry as we are today about communication and information technology.

The difference between nitrates and nitrites, for example, was taught in school curriculum. An article appeared in the Daily Dispatch in Brainerd, Minnesota in the 20’s, that gives as an example of a diligent high school student, that he or she would know the difference.    (The Brainerd Daily Dispatch (Brainerd, Minnesota).  17 January 1923.  Page 3.)

Following Dr. Polenski’s observation, the German scientist, Notwang confirmed the presence of nitrite in curing brines in 1892, as observed by Dr Polenski, but attributed the reduction from nitrate to nitrite to the meat  tissue itself.  The link between nitrite and cured meat colour was finally established in 1899 by another German scientist, K. B. Lehmann in a simple but important experiment.

Karl Bernhard Lehmann (September 27, 1858 – January 30, 1940) was a German hygienist and bacteriologist born in Zurich.

In an experiment he boiled fresh meat with nitrite and a little bit of acid.  A red colour resulted, similar to the red of cured meat.  He repeated the experiment with nitrates and no such reddening occurred, thus establishing the link between nitrite and the formation of a stable red meat colour in meat. (Lee Lewis, W., 1925: 1243)

In the same year, another German hygienists, K. Kisskalt, confirmed Lehmann’s observations but proved that the same red colour resulted if the meat was left in saltpeter (potassium nitrate) for several days before it was cooked. (Lee Lewis, W., 1925: 1243)

K. B. Lehmann made another important observation that must be noted when he found the colour to be soluble in alcohol and ether and to give a spectrum showing an absorption band just at the right of the D line, and a second band, often poorly defined, at the left of the E line. On standing, the color of the solution changed to brown and gave the spectrum of alkaline hematin, the colouring group (Hoagland, Ralph.  1914).

The brilliant British physiologist and philosopher, John Scott Haldane weighed in on the topic.  He was born in 1860 in Edinburgh, Scotland. He was part of a lineage of important and influential scientists.  (Lang, M. A. and Brubakk, A. O. 2009.  The Haldane Effect)

J. S. Haldene contributed immensely to the application of science across many fields of life.  This formidable scientist was for example responsible for developing decompression tables for deep sea diving used to this day.  (Lang, M. A. and Brubakk, A. O. 2009.  The Haldane Effect)

“Haldane was an observer and an experimentalist, who always pointed out that careful observation and experiments had to be the basis of any theoretical analysis. “Why think when you can experiment” and “Exhaust experiments and then think.” (Lang, M. A. and Brubakk, A. O. 2009.  The Haldane Effect)

An interesting anecdote is told about him from the time when he was studying medicine  in Jena.  He apparently carefully observed the amount of beer being drunk, noting that the students on the average drank about 20 pints per evening.”  (Lang, M. A. and Brubakk, A. O. 2009.  The Haldane Effect)

Before we look at Haldene’s contribution, let us re-cap what has been determined thus far.

Polenski and Notwang discovered that nitrite were present in a mix of saltpeter and salt, after a while, even though no nitrite were present when the brine was mixed.

Karl Bernhard Lehmann linked nitrite conclusively with the reddening effect of fresh meat that was boiled in a nitrite and water solution with some free acid.  He also showed that this does not happen if fresh meat is placed in saltpeter and water solution and boiled immediately.   K. Kisskalt showed that the same reddening occurred if fresh meat is left in saltpeter for some time.

K. B. Lehmann managed to “isolate” the colour by dissolving it in ether and alcohol and analyze it spectroscopically.

What S. J. Haldele did was to apply the same rigor to cured meat and became the first person to demonstrate that the addition of nitrite to hemoglobin produce a nitric oxide (NO)-heme bond, called iron-nitrosyl-hemoglobin (HbFeIINO). (Lang, M. A. and Brubakk, A. O. 2009:  119)

Nitrite is further reduced to nitric oxide (NO) by bacteria or enzymatic reactions and in the presence of muscle myoglobin forms iron-nitrosyl-myoglobin. It is nitrosylated myoglobin that gives cured meat, including bacon and hot dogs, their distinctive red color and protects the meat from oxidation and spoiling. (Lang, M. A. and Brubakk, A. O. 2009: 119)

This is how he did it.  He concluded (1901) that its red colour is due to the presence of the nitricoxid hemochromogen resulting from the reduction of the coloring matter of the uncooked meat, or nitric-oxid hemoglobin (NO-hemoglobin). (Hoagland, Ralph.  1914)

Remember the observation made by K. B. Lehmann that the colour of fresh meat cooked in water with nitrites and free acid to give a spectrum showing an absorption band just at the right of the D line, and a second band, often poorly defined, at the left of the E line.  (Hoagland, Ralph.  1914)

Haldene found the same colour to be present in cured meat.  That it is soluble in water and giving a spectrum characteristic of NO-hemoglobin. The formation of the red color in uncooked salted meats is explained by the action of nitrites in the presence of a reducing agent and in the absence of oxygen upon hemoglobin, the normal coloring matter of fresh meats. (Hoagland, Ralph.  1914)

Ralp Hoagland (1908) studied the action of saltpeter upon the colour of meat and found that its value as an agent in the curing of meats depends upon the nitrate’s reduction to nitrites and the nitrites to nitric oxid, with the consequent production of NO-hemoglobin.  The red colour of salted meats is due to this compound.  Hoagland conclusively shows that saltpeter, as such, has no value to preserve the fresh colour. (Hoagland, Ralph,  1914: 212)

The reason why the knowledge did not translate to a change in curing brines was very simple.  The technology and infrastructure did not exist to produce enough nitrite commercially to replace saltpeter.  This means that to produce nitrite was very expensive.

There were some attempts to capitalise on the knowledge gained.  The German scientist,  Glage (1909) wrote a pamphlet where he outlines the practical methods for obtaining the best results from the use of saltpeter in the curing of meats and in the manufacture of sausages. (Hoagland, Ralph,  1914: 212, 213)

Saltpeter can only effect the colour of the meat if the nitrate in the saltpeter is reduced to nitrite.  Glage gives for the partial reduction of the saltpeter to nitrites by heating the dry salt in a kettle before it is used.  It is stated that this partially reduced saltpeter is much more efficient in the production of color in the manufacture of sausage than is the untreated saltpeter. (Hoagland, Ralph,  1914: 212, 213)

The fear of nitrites

The lack of a large scale production process for sodium nitrite and the engineering to build these plants were however not the only factors preventing the direct use of sodium nitrite in meat curing brines.  As one review literature from the late 1800’s and early 1900’s, one realises that a major hurdle that stood between the use of sodium nitrites in meat curing was the mistrust by the general public and authorities of the use of nitrites in food.  The matter relate to the high level of toxicity of nitrite, a matter that will be dealt with separately in Bacon and the art of living.

The first recorded direct use of nitrite as a curing agent was in 1905 in the USA where it was used in secret. (Katina, J.  2009)   The USDA finally approved its use as a food additive in 1906. (porkandhealth)  This did not mean that the public would accept it.

Sodium Nitrite started to be used in this time as a bleach for flour in the milling industry.  Several newspaper articles reveal public skepticism and the great lengths that the scientific community and industry had to go to in order to demonstrate its safety as a bleaching agent  for flour.  An article appeared in The Nebraska State Journal Lincoln, Nebraska on 29 June 1910 entitled,  “All for bleached flour.  No harm can come from its consumption says experts”.  The article deals with a federal court case about the matter and interestingly enough, it seems from newspaper articles that the government was opposing its use.  Many other examples can be sited.

There is a 1914 reference in the London Times that shows the general view of nitrite as not just restricted to the USA.  The article appeared on 9 June 1914 and a reference is made to sodium nitrite where it is described as “a dangerous drug with a powerful action on the heart.”  (The London Times. 1914.  Page 118)  The reference was to the use of nitrite for certain heart conditions.

It is interesting that sodium nitrite did not find an immediate application in the meat industry, even after it was allowed in 1906 in the USA.

In my view, this points to problems surrounding availability and price.  If the issue was the public perception alone, this could have been overcome with a PR campaign by the meat industry as was successfully done by the milling industry.

On 13 Dec 1915 George F. Doran from Omaha, Nebraska,  filed an application for a patent for a curing brine that contained nitrites.  His application strengthens the evidence that it was not the knowledge of nitrite and its role in curing that was lacking, but availability and price.  He states the objective of his patent application to “produce in a convenient and more rapid manner a complete cure of packing house meats; to increase the efficiency of the meat-curing art; to produce a milder cure; and to produce a better product from a physiological standpoint.”

One of Doran’s sources of nitrite is “sterilized waste pickling liquor which he [I have] discovered contains soluble nitrites produced by conversion of the potassium nitrate, sodium nitrate, or other nitrate of the pickling liquor when fresh, into nitrites. . .”   “Waste pickling liquor is taken from the cured meats.  Nitrites suitable for use in carrying out the present invention may be produced by bacterial action from nitrates and fresh pickling liquor by adding a small percentage of old used pickling liquor. The bacteria in old pickling liquor are reducing bacteria and change nitrates to nitrites.”  (Process for curing meats. US 1259376 A)

The use of old pickle has been described much earlier than Doran’s patent.  His usage of old pickle when he understood the reduction of nitrate to nitrite and nitrite’s role in curing along with the fact that sodium nitrite was available can point to only one reason – price.   It comes 10 years after sodium nitrite was first tested in curing brines for meat and shows that it has never become the curing agent of choice most probably due to limited availability and price.  Much more about this later.

The post WWI era (1918 and beyond)

US troops marching

After WWI something changed.  Saltpeter (potassium or sodium nitrate) has been substituted by the direct addition of nitrite to the curing brines.

The question is who pioneered this.  Why and how did sodium nitrite production become so commonplace that it became available to bacon curing plants around the world?

Industry developments like this do not happen “by itself.”  Someone  drives it in order for it to become general practice in an industry.

Chilean Saltpeter is a good case in point.  Even though natural sodium nitrate deposits were discovered in the Atacama desert, it took a considerable effort on the side of the producers (mainly the Chilean Government) to work out the benefits of sodium nitrate and to market it to the world.  It is, for example, famously reported that the first shipment to Britain was dumped in the sea before the ship docked on account that the cargo attracted customs duty and the ships owners could not see any commercial application for sodium nitrate. (2)

In the same way, the direct application of nitrite in curing brines must have been driven by someone.

The Griffith Laboratories, Inc.

The Chicago based company of Enoch Luther Griffith and his son, Carroll Griffith started to import a mixture of sodium nitrite and salt as a curing substitute for saltpeter from Germany in 1925.  The product was called Prague Salt (Prague Powder, 1963: 3)

The Griffith Laboratories (3) played a key role in marketing the new curing brine in the USA.    They took the concept of the Prague Salt (sodium nitrite) and in 1934 announced an improved curing brine, based on the simple use of sodium nitrite, where they fuse nitrite salt and sodium chloride in a particular ratio.  They called it Prague Powder.  Their South African agents, Crown Mills (4), brought the innovation to South Africa. (Prague Powder, 1963: 3, 4)

It is fair to assume that if Prague Salt was being sold to Griffith in the 1920’s, the German producers must have sold it to other countries and companies around the world also.

The benefits of Prague Salt and later Prague Powder over Saltpeter is dramatic.  Prague Salt (sodium nitrite) does not have the slightly bitter taste of saltpeter (Brown, 1946:  223).  It allows for greater product consistency since the same percentage of nitrate was not always present in the saltpeter and the reduction of nitrate to nitrite takes longer or shorter under various conditions (Industrial and Engineering Chemistry, December 1925: 1243).  The big benefit was however in the curing time required.  Instead of weeks or even months that is required with saltpeter, curing could now be done in days or even hours with sodium nitrite.  (The Food Packer, 1954:  64)  From there, brand names like Quick Cure or Instacure.

This means that we have narrowed the time line for invention of Prague Salt (Sodium Nitrite) to between 1914, the beginning of the Great War and 1925 when Griffith imported it from Germany.

However, a document, published in the USA in 1925 shows that sodium nitrite as curing agent has been known well before 1925.

The document  was prepared by the Chicago based organisation, The Institute American Meat Packers and published in December 1925.  The Institute  started as an alignment of the meat packing companies set up by Phil Armour, Gustavus Swift, Nelson Morris, Michael Cudahy, Jacob Dold and others with the University of Chicago.

A newspaper article about the Institute sets its goal, apart from educating meat industry professionals and new recruits, “to find out how to reduce steers to beef and hogs to pork in the quickest, most economical and the most serviceable manner.”   (The Indiana Gazette.  28 March 1924).

The document is entitled, “Use of Sodium Nitrite in Curing Meats“, and it it is clear that the direct use of nitrites in curing brines has been practiced from earlier than 1925. (Industrial and Engineering Chemistry, December 1925: 1243)

The article begins “The authorization of the use of sodium nitrite in curing meat by the Bureau of Animal Industry on October 19, 1925, through Amendment 4 to B. A. I. Order 211 (revised), gives increased interest to past and current work on the subject.”

Sodium Nitrite curing brines would therefore have arrived in the USA, well before 1925.

It continues in the opening paragraph, “It is now generally accepted that the salpteter added in curing meat must first be reduced to nitrite, probably by bacteria, before becoming available as an agent in producing the desirable red color in the cured product.  This reduction is the first step in the ultimate formation of nitrosohemoglobin, the color principle.  The change of nitrate to nitrite is by no means complete and varies within considerable limits under operating conditions.  Accordingly, the elimination of this step by the direct addition of smaller amounts of nitrite means the use of less agent and a more exact control.”

Griffith describes the introduction and origin of Prague Salt and later, Prague Powder as follows in official company documents:

The mid-twenties were significant to Griffith as it had been studying closely a German technique of quick-curing meats.  Short on manpower and time, German meat processors began curing meats using Nitrite with salt instead of slow-acting saltpeter, potassium nitrate. This popular curing compound was known as “Prague Salt.”  (Griffith Laboratories Worldwide, Inc.)

The World War One link

The tantalizing bit of information from Griffith sets World War One as the background for the practical and large scale introduction of direct addition of nitrite into curing brines through sodium nitrite.

There has to be more to the reason for saltpeter being replaced by sodium nitrite as curing agent than the reasons given by Griffith.  For starters, the meat industry has always been under pressure to work fast with less people due to pressure on profit margins.  The need to cure meat quicker due to short manpower and time as a result of the war could not be the full story.

The World War One link from Griffith does not give all the answers, but it puts the introduction of sodium nitrite to meat curing between 1914 and 1918, at least 7 years before Griffith started to import Prague Salt.

A document from the University of Vienna would fill out the story.  According to it, saltpeter was reserved for the war effort and was consequently no longer available as curing agent for meat during World War One. (University of Vienna). It was reserved for the manufacturing of explosives, and for example, the important industry of  manufacturing nitrocellulose, used as base for the production of photographic film, to be employed in war photography.  (Vaupel, E.,  2014: 462)  It gets even better.  Not only did the prohibition on the use of saltpeter expand the information from Griffith as to why people started using sodium nitrite (macro movements in culture does not take place because of one reason only), but it provide a name to the prohibition.

In August 1914, the War Raw Materials Department (Kriegsrohstoffabteilung or KRA) was set up under the leadership of Walther Rathenau.  It was Rathenau who was directly responsible for the prohibition on the use of salpeter.  (5)  He therefore is the person in large part responsible creating the motivation for the meat industry in Germany to change from saltpeter to sodium nitrite as curing medium of choice for the German meat industry during Wold War One.

Walter Rathenau’s actions may have motivated the change, but it was the developments in synthesizing ammonia, sodium nitrate and sodium nitrite which provided the price point for the compound to remain the curing agent of choice, even after the war and after the prohibition on the use of saltpeter was lifted.

Atmospheric Nitrogen

One of the most important scientific riddles to be solved in the late 1800’s/ early 1900’s was how to produce ammonia and its related chemicals from atmospheric nitrogen.  Sir William Crookes delivered a famous speech on the Wheat Problem at the annual meeting of the British Association for the advancement of Science in 1898.

In his estimation, the wheat production following 1897 would seriously decline due to reduced crop yields, resulting in a wheat famine unless science can step in and provide an answer.  He saw no possibility to increase the worlds wheat yield under the prevailing agricultural conditions and with the increase in the world population, this posed a serious problem.  He said,  “It is clear that we are taxed with a colossal problem that must tax the wits of the wisest.”  He predicted that the USA who produced 1/5th of the worlds wheat, would become a nett importer unless something change.  He pointed to the obvious answer of manure, but observed that all available resources  are being depleted fast.

Sir William saw a  “gleam of light in the darkness” and that “gleam” was atmospheric nitrogen.  (Otago Witness.  3 May 1900, Page 4)

It was the German Chemist, Fritz Harber who solved the problem, with the help of Robert Le Rossignol who developed and build the required high pressure device to accomplish this. (www.princeton.edu)

In 1909 they demonstrated that they could produce ammonia from air, drop by drop, at the rate of about a cup every two hours.  “The process was purchased by the German chemical company BASF (a coal tar dye supplier), which assigned Carl Bosch the difficult task of scaling up Haber’s tabletop machine to industrial-level production.  Haber and Bosch were later awarded Nobel prizes, in 1918 and 1931 respectively, for their work in overcoming the chemical and engineering problems posed by the use of large-scale, continuous-flow, high-pressure technology.”  (www.princeton.edu)

“Ammonia was first manufactured using the Haber process on an industrial scale in 1913 in BASF’s Oppau plant in Germany.”  (www.princeton.edu)

It was the vision and leadership of Walther Rathenau, the man responsible for restricting the use of saltpeter, that drove Germany to produce synthesized Chilean Saltpeter.  He saw this as one of the most important tasks of his KRA.  He said:  “I initiated the construction of large saltpeter factories, which will be built by private industries with the help of governmental subsidies and will take advantage of recent technological developments to make the import of saltpeter entirely unnecessary in just few months“.  (Lesch, J. E.,  2000:  1)

Fritz Harber was one of the experts appointed by Rathenau to evaluate a study on the local production of nitric acid.

During World War One production was shifted from fertilizer to explosives, particularly through the conversion of ammonia into a synthetic form of Chile saltpeter, which could then be changed into other substances for the production of gunpowder and high explosives (the Allies had access to large amounts of saltpeter from natural nitrate deposits in Chile that belonged almost totally to British industries; Germany had to produce its own). It has been suggested that without this process, Germany would not have fought in the war, or would have had to surrender years earlier.”  (www.princeton.edu)

So it happened that Germany became the leader in the world in synthesised sodium nitrate production and it effectively replaced its reliance on saltpeter from Chile with sythesised  sodium nitrate, produced by BASF and other factories.

So, as a result of the First World War, sodium nitrite was produced at levels not seen previously in the world and in large factories that was build, using the latest processing techniques and technology from a scientific and an engineering perspective.  Sodium nitrite, like sodium nitrate was being used in the production of explosives.  Nitroglycerin is an example of an explosive used extensively by Germany in World War One that uses sodium nitrite in its production.  (Wikipedia.org.  Nitroglycerin and  Amyl Nitrite)

Ball-and-stick model of Amyl nitrite used in the production of nitroglycerin. Amyl nitrite is produced with sodium nitrite. The diagram shows the amyl group attached to the nitrite functional group.
Ball-and-stick model of Amyl nitrite used in the production of nitroglycerin. Amyl nitrite is produced from sodium nitrite. The diagram shows the amyl group attached to the nitrite functional group.

Sodium nitrite and the coal-tar dye industry

The importance of the manufacturing cost of nitrite and the matter surrounding availability can be seen in the fact that sodium nitrite has been around since well before the war.  Despite the fact that it was known that nitrite is the curing agent and not nitrate, and despite the fact that sodium nitrite has been tested in meat curing agents, probably well before the clandestine 1905 test in the USA,  it did not replace saltpeter as the curing agent of choice.  My hunch is that it did not enter the meat industry as a result of cost.

The technology that ultimately is responsible for synthesising Chilean Saltpeter and made low cost sodium nitrite possible was being incubated in the coal-tar dye and textiles industry and in the medical field.  The lucrative textiles and dye industry was the primary reason for German institutions of education, both in science and engineering to link with industry, resulting in a strong, well organised skills driven German economy. For example, “Bayer had close ties with the University of Göttingen, AGFA was linked to Hofmann at Berlin, and Hoechst and BASF worked with Adolph Baeyer who taught chemists in Berlin, Strasbourg, and Munich.” (Baptista, R. J..  2012:  6)

“In the late 1870s, this knowledge allowed the firms to develop the azo class of dyes, discovered by German chemist Peter Griess, working at an English brewery, in 1858.  Aromatic amines react with nitrous acid to form a diazo compound, which can react, or couple, with other aromatic compounds.” (Baptista, R. J..  2012:  6)

Nitrous acid (HONO) is to nitrite (NO2-) what nitric acid (NO3) is to nitrate (NO3-).

According to K. H. Saunders, a chemist at Imperial Chemical Industries, Ltd., Martius was the chemist to whom the introduction of sodium nitrite as the source of nitrous acid was due.   (Saunders, K. H., 1936:  26)

The economic imperative

The simple fact is that ammonia can be synthesized through the direct synthesis ammonia method at prices below what can be offered through Chilean Satlpeter.  (Ernst, FA.  1928: 92 and 100)  Sodium Nitrite can be supplied at prices below Chilean saltpeter and this made sodium nitrite the most effective curing agent at the lowest price since World War One.

As an example of the cost differences, the price of Nitric Acid (HNO3) from direct synthesis in 1928 was $23.60 per ton HNO3 plus the cost of 606 lb. of NH3 by-product  and from Chilean Nitrate at $32.00 per ton of HNO3, plus the cost of 2840 N NO3 by-product.  (Ernst, FA.  1928: 112)

The advantage of scale and technology

By 1927, Germany was still by far the worlds largest direct syntheses ammonia producer.  Production figures of the year 1926/ 1927  exceeded Chilean saltpeter exports even if compared with the highest levels of exports that Chilean saltpeter ever had in 1917.  A total of 593 000 tons of nitrogen was fixed around the world in 1926/27.  Of this figure, Germany produced 440 000 tons or 74%.  The closest competitor was England through the Synthetic Ammonia and Nitrates Ltd. with a total capacity of 53 000 tons of nitrogen per year.  (Ernst, FA.  1928: 119, 120)

In the USA 7 direct synthesis plants were in operation with a combined capacity of 28 500 tons of nitrogen per year.  (Ernst, FA.  1928: 120)

Supporting evidence from the USA

The thesis that before the war, the production of sodium nitrite was not advanced enough for its application in the meat industry (resulting in high prices and low availability) is confirmed when we consider the situation in the USA.

The first US plant for the fixation of atmospheric nitrogen was build in 1917 by the American Nitrogen Products Company at Le Grande, Washington.  It could produce about one ton of nitrogen per day.  In 1927 it was destroyed by a fire and was never rebuild. (Ernst, FA, 1928: 14)

An article in the Cincinnati Enquirer of 27 September 1923 reports that as a result of cheap German imports of sodium nitrite following the war, the American Nitrogen Products Company was forced to close its doors four years before the factory burned down.  The imports referred to, was as a result of Germany selling their enormous stockpiles of sodium nitrite at “below market prices” and not directly linked to a lower production price in Germany, even though this was probably the case in any event. ( The Cincinnati Enquirer ( Cincinnati, Ohio), 27 September 1923. Page 14.)

The Vienna University document indicate that the fast curing of sodium nitrite was recognised and the ban was lifted when the war ended.  It was this fact that Griffith picks up on in their literature.

This is how it happened that sodium nitrite replaced saltpeter as curing salt.

Conclusion

The ban on the use of saltpeter for non military uses by Walther Rathenau is the likely spark that caused butchers to look at alternative curing systems.  A known alternative was sodium nitrite.  Despite a similar ban on the use of nitrite, later imposed for concerns over the safety of nitrite in meat and because sodium nitrite was also used to produce explosives,  it was available in such large quantities around Germany that it was possible to defy the ban. 

The likely consequence of the developments surrounding the production of atmospheric nitrogen is that sodium nitrite was being produced at prices that was previously not possible.  These prices, combined with the volume of sodium nitrite now available made it a viable proposition to replace saltpeter in meat curing and to remain the curing brine of choice, following the war.

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Notes

(1) “The red color of fresh lean meat, such as beef, pork, and mutton, is due to the presence of oxyhemoglobin, a part of which is one of the constituents of the blood remaining in the tissues, while the remainder is a normal constituent of the muscles. When fresh meat is cooked or is cured by sodium chloride, the red color changes to brown, owing to the breaking down of the oxyhemoglobin into the two constituents, hematin, the coloring group, and the protein, globin.

On the other hand, when fresh meat is cured by means of a mixture of sodium chloride and a small proportion of potassium nitrate, or saltpeter, either as a dry mixture or in the form of a pickle, the red color of the fresh meat is not destroyed during the curing process, the finished product having practically the same color as the fresh meat. Neither is the red color destroyed on cooking, but rather is intensified.” (Hoagland, Ralph.  1914)

(2)   The first export of salitre (sodium nitrate) was authorised by the Chilean government in March 1830 and went to the USA, France, and to Liverpool.  It is the latter shipment which failed and was thrown overboard.  Different sources give different reasons for the action.  One, that price was not attractive,  another, that the excise duties were to high, and a third that the Port captain did not allow the boat to come in because it was carrying a dangerous load.  A few farmers in Glasgow received a few bags.  They used it as fertalizer and reported a three fold increase in crop yield.    (Wisniak, J, et al.  2001:  437)

(3)  Steve Hubbard, Vice President, Global Marketing and Innovation at Griffith Laboratories Worldwide, Inc. graciously provided me with much of the information from company documents.

(4)  Crown Mills was bought out by Bidvest and became Crown National.

(5)   The first War Raw Materials Department (KRA) in Germany was created (KRA) in mid-August 1914,  as suggested by Walther Rathenau.   (Vaupel, E.  2014:  462)  Walter was the son of the founder of AEG and “one of the few German industrialists who realized that governmental direction of the nation’s economic resources would be necessary for victory, Rathenau convinced the government of the need for a War Raw Materials Department in the War Ministry. As its head from August 1914 to the spring of 1915, he ensured the conservation and distribution of raw materials essential to the war effort. He thus played a crucial part in Germany’s efforts to maintain its economic production in the face of the tightening British naval blockade.”

References:

Baptista, R. J..  2012.  The Faded Rainbow: The Rise and Fall of the Western Dye Industry 1856-2000.  From:  http://www.colorantshistory.org/files/Faded_Rainbow_Article_April_21_2012.pdf

Brown, Howard Dexter et al.  1946. Frozen Foods: Processing and Handling

Butler, A. R. and Feelisch, M.  New Drugs and Technologies.  Therapeutic Uses of Inorganic Nitrite and Nitrate From the Past to the Future.  From:  http://circ.ahajournals.org/content/117/16/2151.full

Determination of nitrite in meat products.   University of Vienna, Department of Analytical Chemistry, Food Analytical Internship for nutritionists.

Ernst, FA.  1928.  Fixation of Atmospheric Nitrogen.  D van Nostrand, Inc.

Griffith Laboratories Worldwide, Inc. official company documents.

Hoagland, Ralph.  1914.  Coloring matter of raw and cooked salted meats.  United States Department of Agriculture.  National Agricultural Library.  Digital Collections.

Hwei-Shen Lin.  1978.  Effect of packaging conditions, nitrite concentration, sodium erythrobate concentration and length of storage on color and rancidity development of sliced bologna.   Iowa State University Digital Repository @ Iowa State University

Katina, J. 2009.  Nitrites and meat products.  Czech Association of Meat Processors. http://www.cszm.cz/clanek.asp?typ=5&id=1136

Lang, M. A. and Brubakk, A. O. 2009.  The Haldane Effect.   The American Academy of Underwater Sciences 28th Symposium.Dauphin Island

Lee Lewis, W.  December, 1925.  Use of Sodium Nitrite in Curing Meat.  Industrial and Engineering Chemistry.

Lesch, J. E..  2000.  The German Chemical Industry in the Twentieth Century.  Kluwer Academic Publishers.

Mauskopf, MSH.  1995.  Lavoisier and the improvement of gunpowder production/Lavoisier et l’amélioration de la production de poudre.  Revue d’histoire des sciences

Nitrogen.  University Science Books, ©2011

Otago Witness.  3 May 1900.  Sir William Crookes and the wheat problem.  Issue 2409, Page 4, from:  http://paperspast.natlib.govt.nz/

Péligot E. 1841.  Sur l’acide hypoazotique et sur l’acide azoteux. Ann Chim Phys.; 2: 58–68.

Prague Powder, Its uses in modern Curing and processing.  1963.  The Griffith Laboratories, Inc.

Process for curing meats.  US 1259376 A

Redondo, M. A..  2011.  Effect of Sodium Nitrite, Sodium Erythorbate and Organic Acid Salts on Germination and Outgrowth of Clostridium perfringens Spores in Ham during Abusive Cooling.  University of Nebraska – Lincoln.

Salem, H. et al.  2006.  Inhalation Toxicology, Second Edition.  Taylor & Francis Group, LLC.

Saunders, K. H.  The Aromatic Diazo-Compounds and their technical applications.  Richard Clay and Company.

Scheele CW. 1777. Chemische Abhandlung von der Luft und dem Feuer. Upsala, Sweden: M. Swederus.

The Brainerd Daily Dispatch (Brainerd, Minnesota).  17 January 1923.  Page 3.

The Food Packer.  Vance Publishing Corporation. 1954

The Indiana Gazette, 28 March 1924

The Indiana Gazette.  28 March 1924.

The Nebraska State Journal Lincoln, Nebraska.  Wednesday, June 29, 1910.   All for bleached flour.  No harm can come from its consumption says experts.  Page 3.  

The Times (London, Greater London).   8 June 1914.  Adulteration.  Examples of fraudulent manufacture.  Page 118

The Times (London, Greater London).  1 May 1919.  Government Property for by direction of the Disposal Board.  Explosives and Chemicals.  Prices were coming down in 1920, as reported in The Cincinnati Enquirer ( Cincinnati, Ohio), 2 July 1920. Page 17.

Van Cortlandt, P, et al.  1776.  Essays upon the making of salt-petre and gun-powder.  Published by order of the Committee of Safety of the colony of New-York.

Vaupel, E.  2014.  Die chemische Industrie im Ersten Weltkrieg
Krieg der Chemiker. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Wisniak, J, et al.  The rise and fall of the salitre (sodium nitrate) industry.  Indian Journal of Chemical Technology.  Vol. 8, September 2001, pp 427 – 438.

Wells, D. A.   1865.  The Annual of Scientific Discovery, Or, Year-book of Facts in Science and Art for 1865.  Gould and Lincoln.

Whittaker, CW, et al.  July 1932.    A Review of the Patents and Literature on the Manufacture of Potassium Nitrate with notes on its occurrence and uses.  United Stated Department of Agriculture.  Miscellaneous Publications Number 192.

Click to access freebies_SodiumNitriteFactSheet.pdf

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Haber_process.html

http://www.britannica.com/EBchecked/topic/491966/Walther-Rathenau

en.wikipedia.org/wiki/Nitroglycerin

http://en.wikipedia.org/wiki/Amyl_nitrite

http://en.wikipedia.org/wiki/Amyl_nitrite

Images:

Picture 1:  Smoker trolly with pork belly taken by Eben

Picture 2:  Curing salt taken by Eben

Picture 3:  Atacama Desert.  Photograph by  Dario Lopez-Mills/AP.  Source:  http://www.theguardian.com/science/the-h-word/2014/jun/02/caliche-great-war-first-world-war-conflict-mineral

Picture 4:  World War One:  http://www.excaliburunit.org.uk/#/world-war-1/4580632440

Picture 5:  US troops returning from World War One.  http://www.ww1medals.net/WW1-US-Victory-medals.htm

Picture 6:  Amyl nitrite.  http://en.wikipedia.org/wiki/Amyl_nitrite