Introduction to Bacon & the Art of Living
The story of bacon is set in the late 1800s and early 1900s when most of the important developments in bacon took place. The plotline takes place in the 2000s with each character referring to a real person and actual events. The theme is a kind of “steampunk” where modern mannerisms, speech, clothes and practices are superimposed on a historical setting. Modern people interact with old historical figures with all the historical and cultural bias that goes with this.
narrative – the history of bacon
The Theory of Proteins: Its Birth
Copenhagen, September 1891
Dear kids,
It is the first day of autumn. Denmark is not home, but there is a beauty in 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 find time to go on a long hike. I miss Table Mountain! I miss my mom and sitting by 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 is not Africa! It seems as if 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 saltpetre 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 suspect 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, we must get on the next steamer leaving the Cape for Copenhagen. We decided to get everybody who would 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 built up first, it will never be enough for the first “turn”. As soon as it’s turning, momentum takes over and the engine takes on a life of its own. The initial dreams are the building up of pressure.
It took thousands of years to develop the art of curing meat. 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 saltpetre (1).
Jeppe and I had the best of times at the early morning meetings. Since Minette arrived, it gave our lessons a dynamic character. He would go through the relevant scientific discoveries of the previous few years, pointing out the direct application of science to the art of curing bacon. His lessons give both Minette and me enjoyment that it is hard to communicate. The Monday, following our visit to the University, one of the Chemistry Professors, Dr. Julius Jensen, decided to visit us at the bacon factory. (Chapter 12.06.2: Ammonia from Urine and Horse Sweat-> An Ancient Pathway to Curing) It was a volcanic Monday morning! Ever since that magical day, Jeppe has been looking to get Dr Jensen back for another visit. The planets aligned this week and Dr. Jensen was back for another monumental morning!
Justus von Liebig
He came prepared for our next set of lectures and on our part, we were ready with notebooks, pens, and inquiring minds! He overviewed what we learned at the University from Dr Hans Thirsten (Chapter 12.06.1: From Sea to Deserts -> Sal Ammoniac Predating Saltpetre) and during his first lecture at Jeppe’s factory. The first major character that he introduced us to in the grand drama of the developing understanding of meat was the formidable presence of Justice von Liebig, a man who has been key in the last few letters I wrote where I discussed matters related to nutrition and the industrial application of the emerging science of Chemistry, especially in the United Kingdom.
Justus von Liebig’s education and eventual work with Joseph-Louis Gay-Lussac played a significant role in shaping his career in chemistry. Liebig initially studied at the University of Bonn under Karl Wilhelm Gottlob Kastner, his father’s business associate. When Kastner moved to the University of Erlangen, Liebig followed him there. Liebig left Erlangen in March 1822, partly due to his involvement with the radical Korps Rhenania but also because of his aspirations for more advanced chemical studies.
In late October 1822, Liebig went to study in Paris on a grant obtained for him by Kastner from the Hessian government. 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. In Paris, he worked in the private laboratory of Joseph Louis Gay-Lussac and was also befriended by notable scientists like Alexander von Humboldt and Georges Cuvier. Liebig’s doctorate from Erlangen was conferred on 23 June 1823, a considerable time after he left, as a result of Kastner’s intervention on his behalf. This suggests that while he started his higher education at Bonn and Erlangen, his significant academic and professional development occurred in Paris under Gay-Lussac’s mentorship.
During his time with Gay-Lussac, Liebig mastered methods of analysis and learned to pursue investigations systematically. This experience under Gay-Lussac’s guidance was crucial in developing Liebig’s skills and understanding in chemistry, particularly in analytical methods, which would later be foundational in his own groundbreaking work.
Gay-Lussac’s influence on Liebig was profound, especially in providing him with the rigorous scientific training and exposure to advanced research methodologies that would form the basis of his future contributions to the fields of organic chemistry and agrochemistry. This mentorship was a critical stepping stone in Liebig’s career, setting him on the path to becoming one of the most influential chemists of his time.
In my August letter to Laure (Chapter 12.07.1: Lauren Learns the Nitrogen Cycle), which I am sure you also read, I reported on the 1781 events where the French Chemist, Claude Louis Bertholett became aware that something joined with hydrogen to form ammonia (NH3). I pointed out that three years later, Claude joined Lavoisier who was responsible for unravelling the composition of saltpetre 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 cannot 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)
Joseph-Louis Gay-Lussac was renowned for his pioneering work on gases. His discovery that plant seeds contain a substance rich in nitrogen (azote). This discovery is likely to have occurred before his collaboration with Liebig. The French chemists were leading the world, dominated by people like Gay-Lussac.
With Liebig, the focus of groundbreaking chemical research shifted to Germany particularly the chemistry of protein metabolism. Liebig’s work in this field greatly advanced our understanding of this crucial biological process. Liebig was instrumental in establishing the chemical basis of protein metabolism, emphasizing the role of nitrogen in proteins. He explored how dietary proteins, once ingested, are broken down into amino acids and then reassembled into new proteins in the body. This insight was pivotal in recognizing the dynamic nature of protein in our bodies, linking dietary intake to physical health and development. Liebig’s work laid the foundation for modern approaches in fields like nutrition and meat science, where understanding protein transformation is essential. His contributions to the study of protein metabolism are a cornerstone in the science of nutrition and food chemistry.
Liebig’s career path was shaped by a childhood hero of mine, aleander von Humboldt. It was a meeting between Von Humboldt and Liebig in Paris in the early 19th century that seems to have set Liebig on the legendary career that followed. 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.
At the University of Giessen, Liebig created the most productive school of organic chemistry in existence at the time. Liebig 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 in 1842. Liebig believed that the basis of protein metabolism was chemical. Some believe this is his most important contribution to the subject.
Jeppe paused Dr. Jensen for a moment and reminded us that it was at this time when William Oake was industrializing the bacon curing system as he invented Mild Curing. (Chapter 12.01.1: William Oakes Mild-Cured Bacon) It is unlikely that Oake would have been directly influenced by Liebig but as a you chemistry student hw would have been aware of many of the fundamental concepts.
Dr Jensen picked up where Jeppe left off and offered further insights from the perspective of Chemisty. “Between 1835 and 1840 in Ulster, Northern Ireland, where the young Oake lived and reportedly invented the system, the realms of chemistry, nutrition, and health were shaped by the evolving scientific landscape of the era. During this period, the field of chemistry was transitioning away from its alchemical roots and becoming a more systematic and empirical science. Influential concepts such as John Dalton’s atomic theory were gaining traction, fundamentally altering the understanding of matter at its most basic level.
The burgeoning field of organic chemistry, notably advanced by the man we are discussing, Justus von Liebig, was beginning to shed light on the chemical nature of life processes, although these insights were yet to fully permeate the scientific community in regions like Ulster. In terms of nutrition and health, the understanding was still in its infancy. Basic awareness of the link between diet and health existed, but the roles of specific nutrients, vitamins, and minerals were not clearly defined.
This was a period just before the Great Famine in Ireland, and the heavy reliance on a limited range of food sources, like potatoes, underscored the importance of dietary diversity – a concept not scientifically understood at the time but later highlighted by ensuing events. Medical knowledge was also evolving, with many modern theories of disease and hygiene yet to be developed. In Ulster, these scientific developments were viewed through the lens of immediate practical challenges, such as food security and public health, rather than as part of the cutting-edge scientific discourse. This context offers a backdrop for understanding the regional state of chemistry, nutrition, and health during this transformative period.”
Dr Jensen then returned his focus on Liebig. Liebig was well prepared to make such a contribution on account of his training in France and his own studies in organic chemistry. Dr. Jensen brought along with him a copy of Liebig’s work “Animal Chemistry” (1842). He went to great lengths to explain Liebig’s insights into protein metabolism.
Liebig posited that the growth of an animal’s body, the development of its organs, and the replenishment of lost substances are all reliant on blood composition. He argued that only substances that can be converted into blood should be considered truly nutritious. The key components of blood, according to Liebig, are fibrine and albumen. Fibrine is akin to muscle fiber in its properties, and albumen, found in blood serum, resembles egg white, especially in its behavior when heated. Both fibrine and albumen consist of seven chemical elements, including nitrogen, phosphorus, and sulfur. Notably, despite differences in physical characteristics, fibrine and albumen are identical in their fundamental chemical makeup. They can be transformed into muscle fiber and vice versa. Liebig emphasized that all parts of an animal body that contribute to its structure contain nitrogen, alongside carbon and water elements. He observed that the chief constituents of blood contain about 17% nitrogen, a figure not surpassed by any organ part. This understanding of blood’s composition and its role in nutrition was groundbreaking, linking dietary intake directly to physiological development and function.
The importance of nitrogen in all muscles and blood in this way became known to humanity. It is therefore nothing strange to find nitrogen and its conversion into ammonia, ammonium and nitrate, and nitrite as fundamental to the building blocks of animal life. Just as the same compounds play an essential role in plant nutrition and in all processes of the soil and water in our world.
Dr. Jensen paused for a second to look up and see if we were following. We were hanging on to his every word and he continued. Liebig’s research demonstrated that the animal body cannot generate basic elements like carbon or nitrogen from substances that lack these elements. Therefore, he concluded that any food suitable for forming blood or building body tissues such as cellular tissue, membranes, skin, hair, or muscle fibers must contain nitrogen. This necessity arises because these organs need nitrogen for their structure and cannot synthesize it from other elements. Additionally, he noted that animals do not absorb nitrogen from the atmosphere in their normal biological processes, further emphasizing the importance of dietary nitrogen.
Liebig observed that the dietary process in carnivorous animals is relatively straightforward. These animals consume the blood and flesh of herbivores, which chemically, is very similar to their own body composition. Essentially, in sustaining their life processes, carnivores are replenishing their bodies with similar substances to those they are composed of. On the other hand, herbivores, which have more complex digestive systems, primarily eat plants that generally have low nitrogen content. However, Liebig noted that the parts of plants that do provide nutrition to animals are those rich in nitrogen. This led to the understanding that animals need these nitrogen-rich parts of plants for their survival and health. He pointed out that animals could not survive on plant parts lacking these nitrogenous components. Liebig categorized the nitrogenous nutrients in plants into three types, based on their solubility in water – two being soluble and one insoluble.
Uncle Jeppe again stopped Dr Jensen for a moment and pointed out that further to Liebig’s observations, it’s noteworthy that the dietary habits of herbivores and carnivores reflect the nutritional quality of their respective diets. Herbivores, which primarily consume plants with generally lower nitrogen content, often need to graze continuously throughout the day to meet their nutritional requirements. In contrast, carnivores, feeding on nutrient-rich, nitrogen-heavy diets from the flesh and blood of other animals, typically require feeding less frequently, sometimes only every few days.
Dr Jenses returned to Liebis observations. Liebig identified three key components in plants – vegetable fibrin, vegetable albumin, and vegetable casein – which have characteristics similar to their animal counterparts. Vegetable fibrin, found in plant tissues, mirrors the properties of animal fibrin, a protein essential in blood clotting and muscle structure. Vegetable albumin, similar to animal albumin, is a soluble protein found in plants, playing a role analogous to albumin in animals, which is vital for maintaining osmotic pressure in the blood. Lastly, vegetable casein, akin to animal casein found in milk, is a plant protein with significant nutritional value, contributing to growth and development.
He marveled at the simplicity and beauty revealed by these discoveries in understanding animal nutrition and organ formation. These plant-based components, when consumed by animals, contribute directly to blood formation, as they already contain fibrine and albumen, essential blood components. Thus, Liebig concluded that the growth and development of an animal’s body rely on absorbing these specific substances from plants, which are analogous to the vital elements in their blood. This understanding bridged the gap between plant nutrients and their direct role in forming animal tissues, emphasizing the interconnectedness of plant and animal life at a nutritional level.
Liebig’s view on nitrogen in nutrition is summarized by himself as follows: . . . Human food can be broadly categorized into two types: nitrogen-containing (nitrogenised) and non-nitrogen-containing (non-nitrogenised) substances. The nitrogenised foods, which include things like plant-based fibrin, albumin, casein, as well as animal flesh and blood, are crucial for blood formation and consequently, for building the body’s tissues. On the other hand, non-nitrogenised foods, which encompass fats, starches, various sugars, and alcoholic beverages, primarily aid the respiratory process. He referred to the nitrogenised foods as the ‘plastic elements of nutrition’, essential for building and maintaining the body’s structure, while the non-nitrogenised foods were termed ‘elements of respiration’, serving to fuel the body’s energy needs.
Dr. Jensen pointed out 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 (for 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)
In the context of modern bacon curing, there’s a noteworthy application of Liebig’s principles, particularly in relation to protein digestion and its impact on curing processes. It has been observed that the foaming behavior during bacon curing is related to the length of amino acid chains remaining after proteins are broken down, or ‘digested’, with an acid. This correlation became evident when attempting to dissolve the products of these acid digestion experiments in water. For bacon curers who need to use such digested proteins in their curing brine, managing excessive foaming is crucial. One practical solution is to extend the duration of protein digestion in the acid. This extended digestion process breaks down the proteins further, resulting in shorter amino acid chains that are less likely to cause foaming when rehydrated and incorporated into the curing brine. This approach not only mitigates foaming issues but also aligns with the fundamental understanding of protein chemistry in food processing.
The Atomic Theory and Birth of Organic Chemistry
At this point Dr. Jensen 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 and a short diversion followed away from Liebig to bring us more up to speed on Dalton.
John Dalton was by all accounts not the brightest of students. Some said that his main characteristic was not being bright but rather, determination. I have to interject that in this regard I am very akin to Dalton. My own chemical ability is mediocre at best, but I am determined! Then again, who am I to compare myself to one such as Dalton?
Dalton was poor and largely self-taught. While there is some overlap in the work of Dalton and Liebig, Dalton’s major contributions were earlier than Liebig’s. Thus, they worked in the same era but their peak periods of scientific contribution were not exactly concurrent. Justus von Liebig build upon the foundational work of John Dalton. Dalton’s atomic theory, which introduced the concept that elements are composed of atoms and that each element has its own kind of atom, laid the groundwork for the development of modern chemistry. Liebig, in his study of agricultural chemistry and protein metabolism, would have utilized the principles of atomic theory to understand and explain the chemical structures and reactions of various compounds. So, lets tirn our attention to Dalton for a moment.
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 gases 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. This development in understanding atomic weights and molecular formulas was foundational for scientists like Liebig and later Mulder in their theories of proteins. Accurate atomic weights allowed for a more precise understanding of chemical structures, including proteins, which are complex molecules composed of carbon, hydrogen, oxygen, and nitrogen. This understanding was critical for advancing the study of protein metabolism and composition.
In the early 1800s, Friedrich Wöhler achieved what may be believed to be 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.”
Friedrich Wöhler’s synthesis of urea in the early 1800s marked a turning point in chemistry, debunking the vitalism theory which posited that organic compounds could only originate in living beings. His success in creating urea, a biological compound, in the lab without any “vital force” laid the groundwork for modern organic chemistry. This breakthrough paved the way for a deeper understanding of proteins, and complex organic molecules. It established that organic compounds, including proteins, could be studied and synthesized through chemical methods, thereby contributing significantly to the development of protein theory and biochemistry.
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 contains 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 oxidized 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 built upon the logic of the atomic theory.
The collaboration between Friedrich Wöhler and Liebig on the concept of a common radical in chemistry was a key advancement in understanding organic molecules, including proteins. They discovered that certain groups of atoms (radicals) in a molecule could be replaced while retaining the molecule’s fundamental structure. This concept of molecular modification and reactivity was instrumental in understanding complex organic molecules like proteins. Their work on radicals, along with Wöhler’s synthesis of urea, demonstrated the chemical nature of organic compounds, setting the stage for a deeper exploration of protein chemistry and metabolism, integrating it with Dalton’s 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 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.
Dr. Jensen reiterated. The building blocks of living organisms are proteins! Proteins are the key ingredient that forms meat! Bacon curing is in the first place related to the manipulation of proteins and if we want any chance to understand the chemical reactions associated with bacon production, we should know the chemistry of proteins. Apart from the manipulation of proteins, it is key in our work to understand the concept of nutrition.
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,
Liebig’s research revealed a fascinating aspect of protein chemistry, particularly in how animal proteins like albumen, fibrine, and casein behave under certain conditions. When these proteins are dissolved in a strong solution of caustic potash (a potent chemical commonly known as potassium hydroxide) and then heated, they undergo a decomposition process. Following this, when acetic acid – a mild acid found in vinegar – is added to this heated mixture, a gelatinous, semi-transparent substance forms as a precipitate. This substance, regardless of whether it originated from albumen, fibrine, or casein, has identical characteristics and composition.
This discovery, initially made by Mulder, showed that this precipitated substance comprises the same organic elements, in the exact same proportions, as the original animal proteins. This was confirmed through meticulous analysis. Essentially, if one were to remove the non-organic parts (like ashes from incineration, sulfur, and phosphorus) from the original proteins and compare the remaining composition to this precipitated substance, the results would match perfectly. This means that the core organic components of albumen, fibrine, and casein remain unchanged in this chemical transformation, a finding that has significant implications in understanding the fundamental nature of these animal proteins. (Munro and Allison, 1964)
Liebig’s perspective on the composition of blood and casein in milk offers a deeper understanding of animal tissue formation. He suggests that these substances are essentially mixtures containing phosphates, various salts, sulfur, and phosphorus. Additionally, they include a compound made up of carbon, nitrogen, and oxygen, where the proportions of these elements are consistent and fixed. This specific compound is crucial because it acts as the foundational building block for all other animal tissues. Essentially, this means that the genesis and development of various tissues in an animal’s body can be traced back to this compound in the blood. This concept highlights the central role of blood in the formation and sustenance of different tissues within the animal body, underscoring the interconnectedness and complexity of biological systems.
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, and fibrine is C48E36. N6014 + P + 2 S, and so on.
– Liebig’s Opposition
Liebig, initially a supporter of Mulder’s protein nucleus theory, eventually turned against it based on his continued research in protein chemistry. In his 1847 book “Researches on the Chemistry of Food,” Liebig argued that Mulder’s basic experiments could not be replicated by several chemists, and Mulder’s formulations of proteins involving sulfur and phosphorus did not align with newer findings. Liebig noted that scientific theories are only valid as long as they incorporate current knowledge and observations. He criticized the protein theory for being based on flawed observations and misinterpretations, lacking a solid foundation and not being widely accepted within the scientific community knowledgeable about its chemistry. This stance marked a significant departure from his earlier enthusiasm for Mulder’s ideas. Liebig’s shift in opinion provoked Mulder, who was frustrated by Liebig’s rejection of a theory he had once endorsed. (Carpenter, 2003)
Despite his criticism, Von Liebig suggests the direction which eventually led researchers to ultimately resolve the structure of the protein molecule. He wrote: … 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)
The term “protein,” as we use it today to describe a vital class of body constituents, interestingly, also serves as a reminder of a historical simplification of protein structure. This term was initially coined with a different meaning than what we associate with it now. In Germany, the word for protein is “Eiweiss,” possibly influenced by Liebig’s eventual rejection of Mulder’s hypothesis about protein structure. Despite this evolution in understanding, it’s important to note that at the core, Berzelius and Mulder’s basic idea was correct: proteins are essential components of the animal body, playing a critical role in almost every physiological process. Over time, the concept of a protein radical, as initially proposed, faded from scientific discourse, and the term “protein” came to be broadly applied to what was previously known as “animal substance.” This shift reflects the dynamic nature of scientific terminology and understanding, adapting as new insights emerge.
Is Protein the only true nutrient?
Dr. Jensen was on a roll, as the kids would call it Nitrogen, as the key nutrient was firmly established, but is this the only one? While he was 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? Von Liebig explained that increased respiration was needed to keep the heart and other tissues from overheating. This led to more oxygen finding its way into the tissues, which unfortunately potentially caused 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 were widely accepted, 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 was, however, a problem with this logic, as was spotted 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 labourers was of lower protein content than that of the less active rich. Now, remember the book, Foods, which we read every night with Andreas and his family. Edward Smith, the author, and a British physician, and physiologist is another scientist of the time who was interested in the welfare of prisoners. He was worried about the stress 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, 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.” ” (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 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)): “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. Liebig emphasized a well-established chemical fact regarding the dynamic nature of the animal body’s main constituents like albumen, fibrine, gelatinous tissues, and caseous matter. He noted that when these elements are in a state of flux or separation, they actively interact with various substances that serve as food for humans and animals. This interaction leads to a noticeable chemical change in the substances they come into contact with. For instance, elements such as sugar, lactose, or starch undergo a reorganization when they meet the sulfur- and nitrogen-rich components of the body, or similar compounds in plants, especially when these compounds are decomposing. This process results in the formation of new compounds that typically cannot be synthesized through ordinary chemical reactions. Liebig’s observation underlines a fundamental aspect of biochemistry, where biological processes lead to chemical transformations independent of standard chemical affinities, showcasing the complexity of metabolic reactions in living organisms.
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 research 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 requires “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.
There can be no doubt that nitrogen is key to the art of bacon curing and the most important macromolecule we are working with is protein. I came to realise that bacon is nothing less than the art of manipulating it. The 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, central to the concepts of 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 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 are intimately connected to our most basic understanding of life itself.
I am downstairs in the living room. Minette passed out 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
(c) eben van tonder
Stay in touch
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.
This was absolutely amazing reading,all about a dream,research,teachers,adventures,people,team,family,balls,implementation,pride,believe,and a lot of hard work,satisfaction.That dream will be successful.
Best Regards
Christo Wessels