Introduction to Bacon & the Art of Living
This is the definitive story of bacon and life. Our story.
The narrative spans the late 1800s and early 1900s, a time when many of the most pivotal advances in bacon curing took place, while blending seamlessly into the 2000s. Each character is based on a real historical figure and woven into events that actually occurred, both past and present. The world carries a steampunk flavour, with modern speech, behaviours, attire, and technology layered over a historical backdrop. The characters interact with one another through the cultural and historical biases of their time, creating a rich interplay between past and present.
The technological journey traced in this work is remarkable. It begins in prehistory and follows the evolution of curing methods across centuries, arriving in the modern day.
But it is also a personal journey. An our-story.
It may have started in Cape Town, but then again, perhaps somewhere else. Maybe on the dusty roads of Asia, in the Turfan Depression, or in cities like Samarkand and Batumi along the Silk Road. Perhaps it crossed the Alps into Hallstatt. Or maybe it began on the Wechsel in Austria, with a farm girl growing up on alpine meat and butter, raised by extraordinary parents and grandparents.
Maybe it began on the banks of the Vaal River and the wide grasslands of the Northern Free State. I’m not sure anymore. And perhaps it doesn’t matter.
Because wherever it began, it continues.
academic – educational
The Curing Molecule
This chapter is designed to give you enough background to understand the fundamentals of curing and appreciate some of its complexities. This is not intended to be a science textbook, so I take the liberty of presenting matters simplified. I don’t, for example, always indicate when I am talking about an ionic compound when I write a simple notation for nitrite as NOO. I also added “Want to know more?” sections for those with a chemical background or who desire a deeper understanding. Let me walk you through these concepts; a breathtaking story awaits! Don’t try and remember all the new terminology or make all the connections in your mind. Simply read this from start to finish without stopping if it gets tough to follow. I assure you that you will remember far more than you can imagine!
What is Meat Curing?
Curing is the art of guiding fresh meat through a transformation which allows it to endure beyond the reach of cold storage, and in doing so, awakens a colour and flavour unlike anything raw flesh can offer. As the process unfolds, two sensory changes become unmistakable. First, a savoury, complex flavour begins to form, at once earthy and bright. Then comes the colour shift, as the meat settles into its distinctive, rosy hue.
But beyond taste and appearance, something else is happening, which is even more important. The meat becomes safer. Microbial threats are pushed back. Spoilage slows. And at the centre of this quiet transformation is a single, invisible actor: nitric oxide (NO). This tiny molecule meets the iron inside hemeproteins and sets off a chain of reactions that stabilise colour, deepen flavour, and guard against decay (Pearson & Gillett, 1996; Pegg & Shahidi, 2000). Let’s delve into the amazing mechanisms at work.
Proteins, Hemeproteins and Oxygen
Muscle is built from proteins. Among the many types of proteins in muscle, the ones most relevant to us are the hemeproteins. These are proteins that carry a heme prosthetic group, a non-protein molecule that enables specialised chemistry such as oxygen binding, electron transfer, and redox reactions (Keilin, 1966; Nicholls and Ferguson-Miller, 2013).
In the curing process, nitric oxide binds to the iron in the protein myoglobin to form nitrosomyoglobin. This reaction produces the stable pink colour of cured meat and helps protect it from oxidation and microbial spoilage (Pegg and Shahidi, 2000; Honikel, 2008). Myoglobin itself is a globular protein located in muscle tissue. It plays an essential role in storing and releasing oxygen within muscle cells. At its core lies a heme group containing an iron atom in the ferrous state (Fe²⁺), which binds oxygen and gives fresh meat its red colour. The structure of myoglobin closely resembles one of the four subunits of haemoglobin, the oxygen-carrying protein found in red blood cells. While myoglobin functions within muscle cells, haemoglobin circulates in the blood. Both proteins contain heme groups and iron atoms capable of binding oxygen, and it is this shared heme group that gives blood and meat their red colour and oxygen-binding abilities.
Heme, in this context, refers specifically to the iron-based component of the protein. At its core is an iron atom embedded in a porphyrin ring. Iron’s biological utility lies in its ability to cycle between two states: Fe²⁺ and Fe³⁺. This redox flexibility allows iron to accept or donate a single electron, making it ideal for electron transport systems. When in the Fe²⁺ (ferrous) state, iron binds oxygen, enabling haemoglobin and myoglobin to store or carry it. When oxidised to Fe³⁺ (ferric), it can no longer bind oxygen. This reversible switching is how the body takes up and releases oxygen precisely where needed. The transition between these two forms can be triggered by surrounding redox conditions, nearby molecules, the binding or release of oxygen itself, or nitric oxide in curing conditions.
This simple cycling between electron states allows iron to serve as a molecular shuttle in various essential systems. In haemoglobin, iron binds and releases oxygen to support transport through the bloodstream. In mitochondria, iron-containing proteins form part of the electron transport chain, passing electrons through a series of carriers to generate cellular energy.
Myoglobin and cytochrome-like proteins involved in meat curing share this same iron centre and redox flexibility. Cytochromes are hemeproteins found in the mitochondria of muscle cells. While they do not influence meat colour, they are crucial for electron transfer in the process that produces ATP—the energy currency of the cell. These cytochrome-like proteins carry iron at their core and undergo redox cycling similar to myoglobin. Their influence on curing is minor, but they are part of the broader biochemical landscape of muscle tissue.
Oxygen is indispensable for energy production because it acts as the final electron acceptor in the mitochondrial electron transport chain. There, it combines with electrons and protons to form water, a reaction that releases energy used to drive ATP synthesis.
Cellular respiration generates ATP in three major stages. First, glycolysis in the cytosol breaks down glucose and releases a small amount of ATP and electron carriers. Second, the Krebs cycle (TCA cycle) in the mitochondria produces large quantities of NADH and FADH₂, molecules that carry electrons. Third, the electron transport chain uses these electrons to generate a proton gradient, which drives the production of ATP via ATP synthase.
The final step, in which oxygen accepts electrons, is catalysed by cytochrome c oxidase, a hemeprotein. Nitric oxide can temporarily bind to the heme or copper centres of this enzyme, slowing respiration under specific conditions such as low oxygen availability or inflammation. This is one way the body uses NO to regulate energy production and avoid oxidative stress.
Although myoglobin is not directly involved in ATP synthesis, it is situated very close to mitochondria in muscle cells and acts as a short-term oxygen store, releasing O₂ where and when it is needed. The proximity of myoglobin to mitochondria allows for rapid diffusion and efficient oxygen use during high activity.
The transition between Fe²⁺ and Fe³⁺ in iron happens on the scale of microseconds and occurs continuously throughout life. This control of redox state is fundamental to sustaining oxygen flow and continuous energy production.
The energy yield from cellular respiration is immense. A single glucose molecule yields around 36 to 38 ATP molecules. Scaled up, the human body generates and uses about 100 watts of energy at rest—the equivalent of a standard light bulb—but does so with remarkable efficiency and self-regulation. It far surpasses man-made systems in precision, responsiveness, and repair.
Nitric oxide does more than stabilise colour in meat. Before binding to the heme iron, free NO molecules have antimicrobial properties, especially against anaerobic pathogens like Clostridium botulinum. Once bound, NO displaces oxygen from the heme group, halting oxidative reactions that would otherwise degrade colour, flavour, and fat. Curing, therefore, achieves what vacuum packaging does physically, but through chemistry: it neutralises oxygen from within. Curing provides both antimicrobial and antioxidative protection, making it one of the most powerful preservation methods known.
Nitric Oxide is Essential for the Body to Function and Meat Curing
Iron’s ability to accept and donate electrons allows it to regulate energy and oxygen use in the body. One of the most damaging molecules produced in our cells is not nitrite, as often falsely claimed, but superoxide. This reactive oxygen species, O₂•⁻, becomes more prevalent as we age. To understand this, we need to examine the role of oxygen in energy metabolism.
ATP, or adenosine triphosphate, is the cell’s primary energy molecule. It is produced mainly in mitochondria through cellular respiration, which involves transferring electrons from nutrients to oxygen. When this system functions well, oxygen is fully reduced to water, and energy is safely stored as ATP. But as we age, the system deteriorates. Instead of accepting electrons as a complete pair, oxygen may take them one at a time. This incomplete reduction leads to the formation of reactive oxygen species like superoxide, hydrogen peroxide, and hydroxyl radicals. These molecules damage proteins, fats, and DNA.
Although superoxide is dangerous, the body has mechanisms to control it. Chief among these is nitric oxide. This small radical molecule, with a single unpaired electron, plays a protective role by regulating how electrons are transferred. NO competes with oxygen for binding to iron in enzymes such as cytochrome c oxidase, the terminal enzyme of the electron transport chain. By smoothing out the flow of electrons, NO helps prevent the partial oxygen reductions that generate radicals.
What makes this especially important with age is that two key changes occur. First, the production of superoxide increases. Second, the body’s ability to generate nitric oxide declines. Nitric oxide is produced in two main ways. Inside the body, the enzyme nitric oxide synthase acts on the amino acid L-arginine to generate NO. Externally, we can take in nitrate and nitrite through food, which the body can convert to NO through several pathways, especially under low oxygen conditions. This makes the dietary intake of nitrite not only safe but increasingly important with age.
In this single paragraph, we have also introduced the two ways curing occurs. First, from within the meat itself, as proteins degrade and L-arginine is broken down to form nitric oxide. Second, by adding nitrate or nitrite during processing and nitrite is converted chemically inside the meat to NO. This dual pathway lies at the heart of meat curing and is the focus of this chapter. But before we return to that, we must understand how nitric oxide functions more broadly.
While nitric oxide performs its main function by binding to heme iron in enzymes like cytochrome c oxidase, it also acts as a defender against radicals. Though NO does not seek out superoxide as a mobile molecule might, it does react with superoxide to form peroxynitrite. Peroxynitrite is reactive, but it is much less likely to initiate the damaging chain reactions caused by free superoxide. Through this reaction, NO blocks the formation of radical cascades and limits cellular harm.
It should now be clear that oxygen, although necessary for life, can also be dangerous. If it is not fully reduced during respiration, it forms radicals that damage cells. Nitric oxide helps prevent this by binding to iron in key enzymes, regulating electron flow and reducing the likelihood of these radicals forming. In the bloodstream, nitric oxide can also bind to haemoglobin. While this does not regulate mitochondrial respiration directly, it controls how much nitric oxide stays in circulation. Haemoglobin can store or release NO depending on oxygen levels in the tissues. This helps ensure blood vessels dilate where needed and oxygen is delivered efficiently. In this way, nitric oxide protects both the inner workings of cells and the broader circulatory system.
This principle also applies to cured meat. Just as NO binds to the iron in mitochondrial enzymes, it binds to the iron in myoglobin. This prevents oxygen from causing oxidation, which would otherwise degrade the colour and flavour of the meat. In both biology and meat curing, the chemistry is shared. NO occupies the iron centre in myoglobin, blocking oxygen-driven redox cycling. This stops the formation of metmyoglobin, the brown pigment that signals spoilage, and protects fats from turning rancid. Whether inside a living cell or in a piece of cured ham, nitric oxide protects by managing oxygen’s powerful, and potentially destructive, chemistry.
In Short
How NO Prevents Radical Formation
Reactive oxygen species (ROS) appear when oxygen undergoes partial, one-electron reductions. NO limits this by:
- Competing with O₂ at metal centres (heme/non-heme), reducing premature oxygen reduction.
- Interacting with metal-containing enzymes to slow electron leak.
- Reacting with radicals (sometimes forming RNS like peroxynitrite, ONOO⁻—which itself is reactive, so context matters).
In meat, NO’s binding to the pigment and its radical-scavenging capacity underpin colour stability and antioxidant effects (Beckman & Koppenol, 1996; Gray, Gomaa & Buckley, 1996; Pegg & Shahidi, 2000).
How is Nitric Oxide Formed?
Nitric oxide, or NO, is formed in the human body through two main biological pathways. The first is the L-arginine pathway, where specialised enzymes known as nitric oxide synthases convert the amino acid L-arginine into nitric oxide and L-citrulline. This route is responsible for most of the nitric oxide produced naturally within the body, especially in blood vessels, the nervous system, and immune cells. The second route is dietary. In this case, nitrate and nitrite present in food are converted into nitric oxide, especially under conditions of low oxygen or low pH. Estimates vary, but it is generally accepted that about 60 – 70% of nitric oxide production comes from the body’s own enzymatic systems, while the remaining 40 – 50% percent is contributed through dietary sources.
These dietary sources include nitrate-rich vegetables such as spinach, beetroot, lettuce, and celery. Another important dietary source is cured meat. Products like bacon and ham contain small, regulated amounts of residual nitrite, which can serve as a substrate for nitric oxide formation inside the body, especially in the acidic environment of the stomach. These nitrites, far from being harmful, can be valuable contributors to maintaining healthy nitric oxide levels, particularly as we age and our natural production declines.
In meat curing, nitric oxide is likewise generated through two primary mechanisms.
The first mechanism is microbial, based on the L-arginine pathway. As meat ages, muscle proteins break down, and L-arginine becomes more accessible within the tissue. Under the right microbial conditions, this L-arginine is converted into nitric oxide. This natural process underpins many so-called “nitrite-free” or “naturally cured” meats. Indeed, many people who try to cure meat without adding nitrite, often motivated by fears rooted in poor science, are surprised when, after several days, their meat begins to develop a pinkish colour, at least in patches. This is the slow result of bacteria converting available L-arginine into nitric oxide, triggering a partial curing effect over time.
The second mechanism is the classic nitrate to nitrite to nitric oxide pathway. Traditionally, nitrate in the form of potassium nitrate, also known as saltpetre, is added to the meat. Bacteria then reduce the nitrate to nitrite, and this nitrite is chemically reduced to nitric oxide, which binds to the heme iron in the meat’s pigment and gives it the characteristic cured colour and flavour. In industrial practice today, the initial bacterial step is often bypassed by using sodium nitrite directly. This ensures a faster, more predictable reaction. Even when vegetable-based curing agents are used, the same chemical sequence applies. Celery or beetroot powders contribute nitrate or nitrite, which is ultimately transformed into nitric oxide within the meat.
It is important to understand that both nitrate-based and L-arginine-based curing depend on microbial activity. For decades, the possibility that L-arginine could serve as a nitrogen source for curing was overlooked. This is partly because when nitrate is present, bacteria tend to use the nitrate rather than L-arginine. The role of L-arginine becomes noticeable only in the absence of nitrate. Early suspicions that L-arginine played a part in long-term dry curing, where only salt was added and colour appeared slowly, were eventually confirmed. In the 1990s, researchers identified that bacteria could mediate this transformation of L-arginine to nitric oxide. Initially, this discovery seemed confined to long-aged products like traditional hams. But in more recent years, commercial fermentation-driven systems have made it possible to cure meat rapidly using bacterial action alone, with no added nitrite or nitrate. In these systems, microbial fermentation produces nitric oxide directly, achieving curing speeds comparable to those using added sodium nitrite.
Still, without the shortcut provided by nitrite, the formation of nitric oxide becomes slower and more variable. Nitrite provides a direct chemical path to nitric oxide formation, removing the need for slow bacterial or enzymatic conversion. Without it, the process depends entirely on the availability of bacteria, the presence of the right enzymes, and optimal conditions of pH, temperature, and microbial balance. This explains why, over centuries, nitrite curing, whether from added nitrate or nitrite, became the most consistent and reliable way to preserve meat safely, develop the desired flavour and appearance, and protect against microbial spoilage.
This sets the foundation for our discussion about curing systems. I have known for many years that bacteria can convert L-arginine into nitric oxide. Yet it took far longer to understand what it would require to use this pathway reliably in a curing system. You cannot simply add salt and expect colour to appear. Colour stability must be managed. The microenvironment must be safe. Biofilm formation must be controlled. The speed of reaction must be accelerated. These things do not happen automatically. They must be engineered with care and knowledge. It is one of the most demanding yet rewarding pursuits in the curing world.
Let us return for a moment to the two main curing reactions we have just considered. They are not simply chemical steps. They represent two different paths, two conceptual maps, by which humans have learned to control microbial and oxidative decay and, at the same time, bring forth flavour and colour in meat. In the course of this chapter, we will return to these reactions repeatedly. The story of bacon is, in essence, the story of these two pathways and how curing has always been about producing nitric oxide as quickly and effectively as possible.
There has long been interest among scientists and curers in finding ways to eliminate the use of nitrite in meat curing. This is mostly due to concerns about nitrite’s possible health risks, concerns which have often been overstated and poorly understood. Bacterial fermentation of L-arginine offers one way to do this. However, right from the outset, I want to make one point abundantly clear. Nitric oxide, nitrite, and nitrate are like three closely linked entities. Where you find one, you find the others. Their reactivity ensures constant interchange. Even if you produce nitric oxide from L-arginine alone, nitrite and nitrate will inevitably form in the meat as well. It is chemically impossible to have cured meat that contains nitric oxide without also generating some nitrite. But this should not be seen as a problem. As we have shown, nitrite plays a vital physiological role in the human body. It is not only safe but also beneficial. And the older we get, the more essential its contribution becomes.
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A closer look at the nitrate-nitrite-nitric oxide sequence in our bodies
It has long been known that the nitrate–nitrite–nitric oxide (NO) pathway operates within the human body and is initiated through dietary intake of nitrate. This pathway is not limited to meat curing. It is a critical physiological system that mirrors the very biochemistry essential for sustaining life. As Weitzberg (2010) and others have shown, the nitrate–nitrite–nitric oxide pathway is far more than a secondary route of nitric oxide generation. Alongside Weitzberg, Jon O. Lundberg (Karolinska Institutet, Sweden) has been a leading figure in uncovering the systemic effects of dietary nitrate, co-authoring foundational studies on its role in human health. Nathan S. Bryan (University of Texas Health Science Center, Houston) has extensively investigated nitrate’s conversion pathways and their importance in cardiovascular regulation. Alan N. Schechter (National Institutes of Health, USA) pioneered the understanding of nitrite as a reservoir for NO, particularly valuable during hypoxic stress. Zhongxin Zhuge (University of California, San Francisco) contributed important mechanistic insights into how tissues convert nitrite to NO, and Mark Gladwin (University of Pittsburgh School of Medicine) is known for his work on nitrite’s reduction to NO in blood and vascular tissue, particularly when oxygen is scarce. Together, these scientists have built a compelling picture of a physiological system that mirrors meat curing and is vital to life itself.
In humans, nitrate (NO₃⁻) is absorbed primarily from food sources such as leafy greens, root vegetables and cured meats. Once in the bloodstream, it becomes concentrated in the salivary glands. Oral bacteria then convert nitrate to nitrite (NO₂⁻), which is swallowed and exposed to the acidic environment of the stomach. Here, in the presence of reducing agents like ascorbic acid (vitamin C) and polyphenols, nitrite is chemically reduced to nitric oxide (NO), especially under low oxygen (hypoxic) or acidic conditions.
These researchers have shown that this is not merely a secondary or backup pathway for nitric oxide production. Rather, the nitrate–nitrite–NO pathway functions as a major regulatory system in its own right. Several lines of evidence show that it complements the classical L-arginine–nitric oxide synthase (NOS) pathway, particularly when the latter is impaired, for instance, during hypoxia or when the availability of L-arginine is limited. In such scenarios, the nitrate–nitrite route ensures continued NO production, safeguarding vital physiological processes.
What makes this so remarkable is that this sequence of nitrate to nitrite to nitric oxide is exactly the same as the chemical reaction that occurs in traditional meat curing with saltpetre or sodium nitrite. Just as this pathway stabilises meat colour and suppresses microbial growth, it maintains vascular tone and protects human tissue from oxidative stress.
Estimates suggest that 30 to 40% of the total NO production in the human body stems from this nitrate–nitrite–NO pathway, with the remaining 60 to 70% generated endogenously via NOS enzymes acting on L-arginine. This dual mechanism not only ensures redundancy in NO production but also allows the body to fine-tune nitric oxide levels under variable physiological and environmental conditions, offering a striking example of how food biochemistry, meat science, and human health converge.
Can we remove nitrogen (nitrate or nitrite) from our diets?
We are all aware of the importance of oxygen to our everyday lives. Without it, life as we know it is not possible. A second element as necessary to life as oxygen is nitrogen. Where does nitrogen come from, and why is it essential to life? Let’s take a step back and consider nitrogen for a moment before returning to nitrate and nitrite in food and the curing chemistry.
The Importance of Nitrogen
Nitrogen is one of the foundational elements of life. In the plant kingdom, nitrogen is taken up from the soil primarily in the form of nitrates or ammonium and becomes incorporated into amino acids, proteins, and nucleic acids, molecules essential for growth, energy transfer, and reproduction. The lush green colour of healthy vegetation is itself a reflection of nitrogen availability, since chlorophyll, the pigment responsible for photosynthesis, contains nitrogen as a central component.
When animals graze on plants, they inherit this nitrogen in an organic, bioavailable form. In fact, the nutritional value of forage and feed is largely dependent on its nitrogen content, which correlates directly with protein content. Numerous early experiments in animal physiology demonstrated a clear link between nitrogen intake and survival. Animals fed diets devoid of nitrogenous compounds rapidly declined in health and, without intervention, succumbed to nitrogen deficiency. In contrast, animals given diets rich in protein, hence, in nitrogen, thrived. These experiments established nitrogen as not just a useful nutrient but an essential one.
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The role of nitrogen in plants
Nitrogen is part of the green pigment of plants, responsible for photosynthesis, called chlorophyll. It is further responsible for a plant’s rapid growth, increasing seed and fruit production, and improving the quality of leaf and forage crops (Plant Nutrients and Lilies). This is important as we will later see how nitrate, nitrite, and nitric oxide not only cure meat and ensure the overall health of our bodies, but also how the same reaction is key to the nutrition of plants. The curing reaction is by no means something foreign. It is vitally important to all aspects of animal and plant life, and humans form part of this group of animals.
Nitrogen as Plant Food
Potassium (K) and nitrogen (N), together with phosphorus (P), are considered the primary nutrients of plants. These are normally lacking in the soil because plants use them for growth and thus deplete it. As we will see, nature replenishes nitrogen, but modern farming has created the demand to add extra nitrogen to the soil. Potassium (K), nitrogen (N), and phosphorus (P) are all part of the macronutrients. The secondary nutrients are calcium (Ca), magnesium (Mg), and sulphur (S). These nutrients are normally abundant in the soil. When lime is applied to acidic soil, large amounts of calcium and magnesium are added. Decomposing organic matter normally yields enough sulphur. Potassium (K) is absorbed in larger volumes than any other mineral element except nitrogen and, in some cases, calcium. It assists in the building of proteins, photosynthesis, and fruit quality, and it reduces disease occurrence (Plant Nutrients and Lilies). The abundance of potassium in plants can be seen from its historical identification, namely, from potash or plant ashes soaked in water in a pot. The name “potassium” is derived from this practice, which predates the Industrial Revolution.
All proteins, the building blocks of muscles, contain nitrogen. Our bodies use nitric oxide to stay healthy in many different ways. To such an extent that life would not be possible without nitric oxide in our bodies. The question is whether the body produces enough nitric oxide on its own. The answer is no. We need to supplement what the body cannot produce through our diet. Some of the foods where we get nitrate or nitrite in our diets are:
Vegetables: By far the most significant source of nitrates is leafy green vegetables. The way that the nitrates end up as nitric oxide in our bodies is through the nitrate-nitrite-nitric oxide sequence. These vegetables also contain nitrites and convert into nitric oxide through the sequence: nitrite → various chemical reactions → nitric oxide.
Water: Borehole water often contains nitrate and nitrite from animal and human waste and fertilisers in surrounding areas. The sequence of reactions that changes the nitrates in water into nitric oxide is the same: nitrate → nitrite → nitric oxide.
Cured Meat: Nitrate salts are found naturally around the world. Potassium nitrate, for example, is known as saltpetre. Nitrite salts are manufactured salts containing sodium and nitrite. Saltpetre (potassium or sodium nitrate) is still used in meat curing today. If we consume cured meat, we ingest nitrates or nitrites, and it changes into nitric oxide in our bodies through either the nitrate-nitrite-nitric oxide or nitrite-nitric oxide sequence. Cured meat, however, is the smallest and most insignificant source of nitrates and nitrites in our diet.
The path from nitrate to nitric oxide is essential to focus on here. Let me illustrate it in greater detail using saltpetre as an example. Saltpetre can be represented as one nitrogen atom and three oxygen atoms, and to make it easy, I will write it as NOOO to focus on the number of oxygen atoms. The astute observer will note that I leave the metal part of the saltpetre out and represent only the nitrate part. Nitrate joins forces with metals like sodium, calcium, or potassium to form sodium nitrate, potassium nitrate (known as saltpetre), or calcium nitrate. In terms of curing meat, only sodium plays a further role, which we will look at later. For now, it is helpful to ignore the first part of the pair and focus only on the nitrate part.
When nitrate connects to one of the metals, it forms a very stable salt that does not easily lose an oxygen atom. We said we represent nitrate in this chapter as NOOO, but you remember that the actual representation is NO₃⁻. The stable molecule now loses an oxygen atom through bacteria that use the extra oxygen atom in their metabolism. So, NOOO loses an oxygen atom through the action of bacteria, and nitrite is formed, which we represent as NOO (actually, NO₂⁻). In contrast to nitrate, nitrite is an unstable molecule and is easily changed to one of the other Reactive Nitrogen Species (RNS), such as nitric oxide. If NOO loses an oxygen atom, NO or nitric oxide is formed. This reaction happens chemically and not through bacteria, and it involves nitrite first changing into other forms before it ends up as nitric oxide.
Ancient curing methods start with nitrate, which is changed to nitrite and nitric oxide. This is how it was done before sodium nitrite became available worldwide after World War I, and many artisan curers still prefer to start with nitrate when they cure meat. The reason is that the bacteria also contribute to the development of flavours in the meat, which one loses if one starts directly with nitrite in sodium nitrite, which does not require bacteria to change into nitric oxide to cure the meat. It became the norm following World War II to skip the step of changing nitrate to nitrite. This is time-consuming and may result in inconsistent curing. The current practice begins the reaction sequence using sodium nitrite rather than nitrate.
Whether we talk about the reaction nitrate-nitrite-nitric oxide or nitrite-nitric oxide, these scenarios are driven by the loss of one oxygen atom at each step. The opposite is also possible because oxygen atoms can be added. At times, nitric oxide can gain an atom to form NOO or nitrite, and NOO can gain another to form NOOO or nitrate. Remember that we said you are likely to find the others where you find one. So, where you have nitrate, nitrite, or nitric oxide, you are likely to find the others. The opposite is also possible, mainly because oxygen atoms can be added. At times, nitric oxide can gain an atom to form NOO or nitrite and NOO to form NOOO or nitrate. Remember that we said that you are likely to find the others where you find one. So, where you have nitrate, nitrite or nitric oxide, you are likely to find the others.
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Ionic compounds
It’s easy to see that the “3” following the O in NO₃⁻ (nitrate) tells us one nitrogen atom is bound to three oxygen atoms—but what does the minus sign mean? The nitrogen plus the three oxygens act as a single charged unit. The net charge of that package is negative (hence the “–”). We call such a charged unit an ion (if it’s a single atom) or part of an ionic compound (if several atoms are joined and carry a net charge). A compound is simply two or more elements grouped together (Atkins & de Paula, 2014; Housecroft & Sharpe, 2012).
Ionic compounds are held together by electrostatic forces between oppositely charged ions. A cation is positively charged; an anion is negatively charged. When they meet in the right proportions, the overall solid is electrically neutral. A familiar example is table salt: NaCl, made of Na⁺ (a cation) and Cl⁻ (an anion).
Nitrogen + oxygen generate a family of oxo‑anions that matter a great deal to curing—nitrate (NO₃⁻) and nitrite (NO₂⁻) foremost among them. Just as “table salt” is the colloquial for sodium chloride, “saltpetre” is the colloquial for potassium nitrate (KNO₃). The nitrate ion (NO₃⁻) pairs with a metal cation (e.g., K⁺, Na⁺, Ca²⁺) to give salts such as KNO₃, NaNO₃, Ca(NO₃)₂. In water, you can think of these salts forming from nitric acid (HNO₃) plus a base like KOH, producing a crystalline salt [K⁺][NO₃⁻] (or more compactly, KNO₃) (Housecroft & Sharpe, 2012).
Likewise, nitrite (NO₂⁻) forms salts with the same metals:
Nitrate salts
- NOOO (nitrate) + K (potassium) → KNO₃ (potassium nitrate)
- NOOO (nitrate) + Na (sodium) → NaNO₃ (sodium nitrate)
- NOOO (nitrate) + Ca (calcium) → Ca(NO₃)₂ (calcium nitrate)
Nitrite salts
- NOO (nitrite) + K (potassium) → KNO₂ (potassium nitrite)
- NOO (nitrite) + Na (sodium) → NaNO₂ (sodium nitrite)
- NOO (nitrite) + Ca (calcium) → Ca(NO₂)₂ (calcium nitrite)
In our meat-curing discussions, we usually ignore the metal (K, Na, Ca) once the salt is dissolved, because the reactive nitrogen species (nitrate, nitrite, nitric oxide) drive the chemistry we care about (Pegg & Shahidi, 2000; Honikel, 2008).
Reduction vs oxidation (in the simple oxygen-counting sense you’re using here)
In the context of nitrogen compounds, reduction and oxidation can be understood in a simplified way by counting oxygen atoms. Reduction refers to the loss of oxygen atoms, while oxidation involves the gain of oxygen atoms. This framework helps us trace the transformations between nitrate, nitrite, and nitric oxide. For example, when nitrate (represented as NOOO or NO₃⁻) loses one oxygen atom, it becomes nitrite (NOO or NO₂⁻), and when nitrite loses another oxygen atom, it forms nitric oxide (NO). This sequence is central to both biological nitric oxide production and traditional meat curing. Conversely, oxidation describes the reverse process: starting from more reduced forms like ammonia (NH₃ or NH₄⁺), oxygen atoms can be added chemically or biologically to generate nitric oxide or proceed further to nitrite and nitrate, depending on the pathway and environmental conditions (Hanrahan, 2005; Lundberg, Weitzberg & Gladwin, 2008). These transformations are not just theoretical but are foundational to life processes and food preservation alike. We will revisit the story of ammonia’s conversion to nitric oxide—particularly through microbial action—when we explore the historical significance of sal ammoniac and related curing practices.
Reduction (losing oxygen atoms)
- NOOO → NOO → NO
- Nitrate (NOOO / NO₃⁻) loses one O → nitrite (NOO / NO₂⁻)
- Nitrite loses one O → nitric oxide (NO)
Oxidation (gaining oxygen atoms)
- Starting from reduced nitrogen species (e.g., NH₃ / NH₄⁺), adding oxygen (biologically or chemically) can yield NO or move further up to NO₂⁻ and NO₃⁻, depending on pathway and conditions (Hanrahan, 2005; Lundberg, Weitzberg & Gladwin, 2008).
We’ll return to the ammonia → NO story (via microbial nitrification/oxidation) when we discuss sal ammoniac and related pathways.
The ever‑presence of nitrogen
Consider how atmospheric nitrogen (N₂) is constantly converted into reactive nitrogen species that flow through plants, animals, water, soil, and the atmosphere. Otto et al. (2010) estimate that roughly 1.4 billion lightning flashes per year produce about 8.6 billion tonnes of NOx—a family of nitrogen oxides. The “x” in NOx simply means the oxygen count varies: NO (x = 1), NO₂ (x = 2), NO₃⁻ (x = 3), etc.
This dwarfs anything the curing industry could contribute. It should end the notion that nitrate, nitrite, or NO are alien “industrial” chemicals foisted on meat: they are everywhere, always cycling, and essential to life (Hanrahan, 2005; Lundberg et al., 2008; Otto et al., 2010).
Nitrite, like NO itself, is highly reactive and therefore less prevalent (and shorter‑lived) in the environment than nitrate, which is far more stable. Humans today produce most dietary sodium nitrite (a manufactured salt), whereas nitrate is abundant naturally—especially in vegetables—and NO is fleeting, rapidly transforming into other nitrogen species (Weitzberg & Lundberg, 2010; Honikel, 2008).
Want to know more
“Nitrogen is an essential element for all forms of life and is the structural component of amino acids from which animal and human tissues, enzymes, and many hormones are made. For plant growth, available (fixed) nitrogen is usually the limiting nutrient in natural systems. Nitrogen chemistry and overall cycling in the global environment are quite complex due to the number of oxidation states. Nitrogen itself has five valence electrons and can be found at oxidation states between −3 and +5. Thus, numerous species can form from chemical, biochemical, geochemical, and biogeochemical processes.” (Hanrahan, 2005)
Global nitrogen species and selected chemical data (Hanrahan, 2005)
| Oxidation state | Species | Functional notes |
|---|---|---|
| +5 | NO₃⁻ (nitrate) | Strong oxidiser; key starting point in curing when reduced to nitrite/NO. |
| +5 | HNO₃ (g/aq) | Nitric acid; industrial source of nitrates. |
| +4 | NO₂ (g) | Brown gas; dimerises to N₂O₄; intermediate in nitrite/nitrate cycling. |
| +3 | HNO₂ (g/aq) | Nitrous acid; unstable precursor to nitrite salts (NO₂⁻). |
| +2 | NO (g) | Nitric oxide; the core curing molecule. Binds myoglobin and stabilises colour. |
| +1 | N₂O (g) | Nitrous oxide (“laughing gas”); minor role in curing but part of nitrogen cycle. |
| 0 | N₂ (g) | Atmospheric nitrogen; inert reservoir for nitrogen fixation. |
| −3 | NH₃ (g) | Ammonia; reduced nitrogen, starting point for nitrification to nitrite/nitrate. |
| −3 | NH₄⁺ (aq) | Ammonium ion; acts as a substrate in microbial pathways leading to NO formation. |
| −3 | NH₄Cl (s) | Ammonium chloride; precursor in some historical curing recipes. |
| −3 | CH₃NH₂ (g) | Methylamine; less relevant to curing but demonstrates reduced nitrogen species. |
The Journey of Nitrogen Through Oxidation States
To truly appreciate the chemistry of curing and the role of nitric oxide (NO), it helps to track how electrons move as nitrogen changes its oxidation state. This movement of electrons, known as redox (reduction–oxidation), is the key to understanding how nitrate (NO₃⁻) becomes nitrite (NO₂⁻), and then NO, and why NO is so powerful in both meat curing and our own bodies.
Think of oxidation states as a measure of how “electron-rich” or “electron-poor” nitrogen is. At −3, nitrogen is fully loaded with electrons (as in ammonia, NH₃). At +5, nitrogen is electron-poor (as in nitrate, NO₃⁻), tightly bound to electronegative oxygens that draw electrons away from it. Every step between these extremes, −3 to +5, represents a partial shift in electron balance.
The Climb from −3 to +5
- Ammonia (NH₃, −3)
- This is fully reduced nitrogen. It has no oxygen attached and is rich in electrons.
- Ammonia is a starting point for nitrification, a bacterial process in soils and water where NH₃ is stepwise oxidised to nitrite and then nitrate (Prosser, 1989).
- Hydroxylamine (NH₂OH, −1)
- Here, an oxygen atom is added, partially pulling electrons away from nitrogen.
- In industrial or microbial systems, this is an intermediate en route to nitrite.
- Nitrous Oxide (N₂O, +1)
- Also called “laughing gas,” this is already oxidised relative to ammonia.
- It’s a side-product in soil microbiology but not particularly important in curing.
- Nitric Oxide (NO, +2)
- The star of curing! NO binds to the iron in heme (myoglobin) to stabilise the pink colour and prevent oxidation (Pegg & Shahidi, 2000; Honikel, 2008).
- NO is formed when nitrite (NO₂⁻) loses one oxygen atom (reduction).
- Nitrite (NO₂⁻, +3)
- The workhorse intermediate in curing.
- It can be reduced to NO (gain of electrons) or oxidised to nitrate (loss of electrons).
- Nitrate (NO₃⁻, +5)
- The most oxidised form.
- Stable, common in plants and water, and the starting point for many curing systems.
- To become active in curing, nitrate must first be reduced to nitrite (often via bacteria or starter cultures).
The Descent from +5 Back to −3
In curing, the focus is on the top half of this ladder—NO₃⁻ (+5) → NO₂⁻ (+3) → NO (+2).
In living systems, however, nitrogen keeps cycling downward, through NO, N₂O, and ultimately back to ammonium (NH₄⁺) or ammonia (NH₃), closing the loop.
This cycle isn’t just a curiosity:
- It drives cellular respiration and energy balance in bacteria.
- It influences oxygen delivery and mitochondrial activity in our own tissues (Lundberg et al., 2008).
- In curing, it controls colour stability, flavour, and shelf life.
Redox in Curing Chemistry
The nitrate → nitrite → NO steps can be summarised like this:
NO₃⁻ (+5) + 2 e⁻ → NO₂⁻ (+3) + O
NO₂⁻ (+3) + e⁻ → NO (+2) + O
In each step, electrons (e⁻) are being added to nitrogen. This is reduction. When we say “the nitrite is reduced to NO,” we literally mean electrons are flowing toward the nitrogen atom, enabling it to break one oxygen bond and form NO.
Conversely, if NO were to re-oxidise back to NO₂⁻ or NO₃⁻, it would lose electrons and gain oxygen.
Why This Matters
Understanding where nitrogen sits on this −3 to +5 ladder allows you to quickly see if a curing reaction (or a biological reaction) is oxidative (moving up, losing electrons) or reductive (moving down, gaining electrons). This is crucial because:
- NO is formed only when nitrogen species are reduced (electron gain).
- Antioxidant systems in curing brines (e.g., ascorbate) work by donating electrons to speed this reduction.
- The ability of NO to stabilise meat colour is linked to its electron-sharing capacity with the heme iron (Fe²⁺), which prevents oxidation to Fe³⁺ (brown metmyoglobin).
Quick recap (using your simplified oxygen-count lens)
We have learned a LOT so far, and it’s time for a quick recap.
- NOOO (NO₃⁻) → NOO (NO₂⁻) → NO
Each step loses an O → we call this reduction here. - The reverse direction, or pathways that add O, we’ll loosely call oxidation.
- Nitrite (NO₂⁻) is the reactive workhorse in curing chemistry: chemically close to NO, able to be reduced quickly, and, crucially, fast, reliable, and controllable (Pegg & Shahidi, 2000; Honikel, 2008; Sebranek & Bacus, 2007).
Demonstrating Oxidation and Reduction
Let’s expand our recap by looking at a few helpful diagrams.
The Nitrate–Nitrite–Nitric Oxide Pathway
Let’s illustrate this with a helpful diagram that illustrates both oxidation and reduction of nitrate found in beetroot.
Nitrate–nitrite–nitric oxide pathway. Adapted from Niayakiru et al., 2020 by Milton-Laskibar (2021).
In the illustration above, beetroot contains nitrate (NOOO / NO₃⁻).
- Step 1: Nitrate loses an oxygen atom (reduction) and becomes nitrite (NOO / NO₂⁻).
This step is typically facilitated by bacteria that use the extra oxygen atom in their metabolism. - Step 2: Nitrite then loses another oxygen atom, creating nitric oxide (NO)—the key curing molecule.
These steps are classic reduction reactions because they involve a loss of oxygen atoms. In curing, NO binds to the heme iron in muscle proteins (e.g., myoglobin), stabilising the desirable pink colour and preventing oxidation to brown metmyoglobin (Fe³⁺) (Pegg & Shahidi, 2000; Honikel, 2008).
However, these reactions are reversible:
- NO can gain an oxygen atom (oxidation) to form NO₂⁻ (nitrite).
- Nitrite can gain another oxygen atom to form NO₃⁻ (nitrate).
- In some cases, NO gains two oxygen atoms directly, forming nitrate (NO₃⁻) without passing through nitrite.
This interplay between reduction and oxidation underpins the nitrogen cycle in curing and in the body.
Biological and Chemical Routes to NO
This second illustration explains the two main pathways of NO formation:
- In the body (enzymatic route)
- L-arginine + O₂ → L-citrulline + NO
- This process is mediated by nitric oxide synthases (NOS), a family of enzymes that produce NO for cellular signalling, blood flow regulation, and immunity (Lundberg, Weitzberg & Gladwin, 2008).
- Outside the body (chemical/bacterial route):
- Nitrate (NO₃⁻) is first reduced to nitrite (NO₂⁻) by bacteria or chemical reactions.
- Nitrite is then reduced to NO, typically aided by reducing agents (e.g., ascorbate) in curing brines or by heat.
Both pathways converge on NO, which is chemically identical whether produced by human cells, bacteria, or curing salts.
Expanded Explanation of Oxidation and Reduction in the NO Cycle
This also refers to the image above – “NO Cycle” diagram
This third graph highlights how oxidation and reduction interconvert NO₃⁻, NO₂⁻, and NO.
- Reduction steps: NO₃⁻ → NO₂⁻ → NO (loss of O atoms, gain of electrons).
- Oxidation steps: NO → NO₂⁻ → NO₃⁻ (gain of O atoms, loss of electrons).
From a formal chemistry perspective:
- NO₃⁻ (+5 oxidation state) is highly oxidised and stable.
- NO₂⁻ (+3 oxidation state) is less stable and can easily move down (to NO) or up (to NO₃⁻).
- NO (+2 oxidation state) is reactive, short-lived, and directly binds to muscle heme proteins in curing.
Changing Perceptions
Meat curing is no longer the only industry to recognise the importance of nitric oxide. The molecule vilified for hundreds of years as purportedly bad for us possesses some remarkable qualities that recently became the intense subject of scientific investigation. Without it, life is not possible, and few people know about it because it was only discovered as late as the 1980s and 1990s.
Nitric oxide turns out to be an extremely important molecule.
Biologically Essential
Years ago, before the importance of nitric oxide was appreciated, consumers looked upon the fact that nitrite (which is very reactive and much more poisonous than nitrate) is used in food with great scepticism. They failed to understand that in nature N (nitrogen) easily and often becomes NO (nitric oxide), NOO (nitrite) or NOOO (nitrate or saltpetre). Also, NOOO (nitrate or saltpetre) often and easily becomes NOO (nitrite) and NO (nitric oxide). Where you find NO, chances are that you will also find NOO and NOOO. Likewise, where you find NOO, you will find NO and NOOO. This is a normal part of the functioning of the human body.
The fact that nitrite is poisonous must be qualified by the statement that nitrite is poisonous under certain conditions. What exactly those conditions are will become a major focus of our study, but simply to say that because something is poisonous under specific conditions, that it is dangerous to include it in food is itself a false assertion.
During this work, I will introduce a very important comparison namely between Oxygen and Nitrogen. Oxygen is like nitrogen in that under certain conditions it is toxic and can lead to death. In fact, it can be stated that ANY cell with a nucleus, as a normal process of the metabolism of the cell, generates both reactive species of oxygen and nitrogen. (Griendling, 2016)
We understand that even oxygen has unintended negative consequences such as ageing us and causing the ultimate demise of the body despite the fact that we recognise it as foundational to life on earth. The same two-edged sword experience is what we encounter in the discipline of curing and it is extremely important to understand it and responsibly ensure that no negative environment exists that may cause the nitrogen species to be harmful to humans in any shape or form.
The facts so far are crystal clear. Nitric Oxide (NO), the curing molecule, as its cousins of nitrate or saltpetre (NOOO) and nitrite (NOO) are essential to human and animal life and the functioning of our bodies. Nitrogen is probably no more or less dangerous than oxygen.
It’s Present in Our Bodies!
Green et al. (1982) measured the concentrations of nitrate (NO₃⁻) and nitrite (NO₂⁻) in various biological fluids and demonstrated that these compounds are ever-present in the human body. Far from being foreign or toxic “additives,” they are normal components of our physiology, continuously cycling through saliva, plasma, gastric juices, urine, and even milk. This highlights the fact that nitric oxide (NO), nitrate (NO₃⁻), and nitrite (NO₂⁻) are integral to human biology.
When discussing nitric oxide (NO), an essential signalling molecule in our blood vessels, immune system, and cellular respiration, or when considering nitrate (NO₃⁻) and nitrite (NO₂⁻), the key is to recognise that these molecules are not toxins by default. Instead, they are naturally occurring compounds critical for maintaining normal physiology. They play roles such as:
- Controlling blood vessel dilation (vasodilation),
- Regulating cellular oxygen balance,
- Participating in immune responses,
- And supporting the formation of beneficial compounds in saliva and gastric fluid.
Therefore, blanket statements like “nitrite is harmful” are scientifically unfounded when viewed outside the context of dose and balance (Lundberg & Weitzberg, 2010; Hord, Tang & Bryan, 2009).
Conclusion: The Molecule that Connects Life, Preservation, and Perception
Nitric oxide is not just a curing agent. It is a molecule that spans the domains of food science, human physiology, and environmental biochemistry. To understand its role in meat curing is to step into a much larger story, one that includes the regulation of blood flow in our arteries, the stabilisation of colour and flavour in our food, the defensive mechanisms of our immune cells, and even the nourishment of plants in the soil.
Throughout this chapter, we have followed the transformations of nitrogen across its many oxidation states. From the reduced ammonium ions in decaying matter to the highly oxidised nitrates in leafy greens, we have seen how nitrogen flows through life in cycles of electron transfer. In meat, this flow is directed to one purpose: the formation of nitric oxide, the molecule that locks colour, delays spoilage, and preserves sensory character. But that same molecule, formed from the same precursors, acts in our blood, lungs, brains, and digestive systems with equal elegance and purpose.
What was once feared as an artificial preservative is, in truth, part of a finely balanced and ancient biological system. The demonisation of nitrite and nitrate in food has often stemmed from an incomplete understanding of chemistry and biology. In reality, these are not foreign chemicals added to food; they are molecules that arise in our saliva, circulate in our blood, and protect us from both infection and oxidative damage.
Curing, therefore, is not a trick imposed on meat to cheat nature. It is an extension of nature’s own chemistry, harnessed by humans to safeguard nourishment, enhance flavour, and honour the biological rhythms of life. We do not simply cure meat, we join an unbroken cycle of molecular transformation that has always sustained life on earth. This is not only a lesson in science, but in respect. Curing is not an artifice; it is a mirror of life itself.
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