Regulations of Nitrate and Nitrite post-1920:  the problem of residual nitrite

Regulations of Nitrate and Nitrite post-1920:  the problem of residual nitrite
By Eben van Tonder
27 August 2017

nitrate and nitrite
Breseola, by Jason Osburn.


I am working in a pork processing plant.  I am not a scientist but I love knowing how things work and have a special love for chemistry.  The health considerations of the use of nitrite and nitrate together in a bacon curing brine are the issue brought about by the fact that it is allowed in South Africa.  I approach the issue from the standpoint of tracking the issues of residual nitrite from a historical perspective.  The entire matter of phenomenally complex and this is at best notes on my personal introduction to the issue.


In South Africa commercial curing brines are still being sold that contain both nitrates and nitrites.  In Europe and America, this is not allowed.  I examine the historical context and the health concerns that gave rise to limiting residual nitrite since the 1920’s  and following the N-nitrosamine hysteria of the 1970’s, the introduction of ascorbate or erythorbate in nitrite brines and the fact that it was made illegal to use nitrate with nitrite in certain classes of bacon. The matter of preservatives in food is always a balancing act.  On the one hand is the potential negative influence on human health of the preservative and on the other hand are the pathogens that the preservative protects us from.  It will become clear that the exact same is at issue in the consideration of nitrite.  A second important aspect is always that of dosage.  Preservatives, in high dosages, are harmful to human health, but at low dosages are less problematic.  An example is alchol which is allowed in human food and drink even though at high dosages, it is harmful.  Nitrite falls somewhat in this category, but the reality of N-nitrosamine formation warrants a far more comprehensive approach to minimise it in bacon than only limiting the dosage of nitrite (even though this by itself is an important strategy).


The story of bacon is the story of nitrate, nitrite and nitric oxide and its ability to preserve meat, imparting a particular cured meat flavour and a characteristic pinkish-reddish cooked-cured meat colour.

The earliest curing agent that imparted these qualities to the meat was nitrate.  The chemical formula for nitrate is CodeCogsEqn (1) .  It is used as an ingredient in gunpowder, as fertiliser and to cure meat.  It was one of the earliest and most enigmatic salts known from antiquity both in the East and the West.  There is a long line of inquiry to try and determine what gives this amazing compound its unique power.  In the West, some scholars likened it to the character of the triune God himself and in the East, in China, it was seen by some as one of the components of the elixir of immortality.

The metals most generally reacting with nitrate (CodeCogsEqn (1)) are the alkali metals, potassium to form saltpeter and sodium to form Chlian saltpeter and sometimes the alkali earth metal, calcium to form calcium nitrate, originally known as Norwegian Saltpeter.  It is most abundantly found naturally in arid regions around the world and it can be made by human action.  By the 1800’s, the technology to produce it was so widespread among German farmers that authors, writing about it, did not even bother to describe the techniques used.

The preserving power of saltpeter is something which I suspect was noticed by ancient civilizations from as early as 5000 BCE.  (Salt – 7000 years of meat-curing)  There is no doubt that these civilizations also noticed its ability to cause meat colour to change from dull brown as it oxidises after slaughter, back to a reddish-pinkish colour and to impart a particular appealing cured meat taste.

It is probable that art of meat curing developed in desert regions in China, probably in the vast Taklimakan Desert in Western China, in the Tarim Bason from where it spread into the heart of Europe.  The nations of Germany, Italy, Spain, Denmark, Holland, England, and Ireland adopted meat curing which was done with salt and a little bit of saltpeter.  In Europe, saltpeter became universal in its inclusion along with salt in meat curing between 1600 and 1750, probably near 1700.  (Lauer K., 1991)

There is evidence to suggest a link between the use of saltpeter and human disease from very early on.  Klaus Lauer (1991) analysed cook books from Germany and Austria between 1540 and 1900 and found some historical parallels between the use of saltpeter in foods and the appearance of colorectal cancer and multiple sclerosis.  Lauder writes,  “According to summarizing works on the history of cancer, large bowel cancer was only seldom reported in the antiquity and Middle-Ages. Its first detailed depictions date from the early 19th century, followed by a rapidly increasing number of reports during the 19th century.”  He notes that “it is of particular interest at what time nitrate or saltpetre was first used in human nutrition,” being at around the same time and increasing as the use of saltpeter in food increased.  (Lauer K., 1991)  There is, however, no record that this was ever noticed at the time.

As alarming as this is, it should be noted that this may prove nothing more than the danger of uncontrolled or highly irregular nitrite levels in meat curing brought about by the use of saltpeter.  Adding nitrate (saltpeter) is, in fact, adding nitrite.  Later we will see that the exact opposite is also true namely that adding only nitrite, is at the same time adding nitrate also since just as bacterial reduction changes nitrates to nitrites, so chemical reactions in the meat matrix change nitrites into nitrates through oxidation.  More about this later.

The people may not have noticed the health impact on the overall population of the use of nitrates, but something that was noticed is the fact that the use of saltpeter in food prevents foodborne toxins.  Kerner in Germany found in a series of studies conducted in 1817, 1820 and 1822 that the outbreaks of sausage poisoning or botulism are linked to the omission of nitrate (saltpeter) in the salt mixture to cure meat for sausage production.    Botulism is an often fatal foodborne disease from the toxins produced by a bacteria, Clostridium Botulinum. (Frences, M. P., et al. 1981)

In a time of superstition and secret remedies, saltpeter was regarded with awe and wonder.  (Saltpeter:  A Concise History and the Discovery of Dr. Ed Polenske)  A newspaper report from 1898 says that saltpeter miners working in a cave has “remarkable health.”  (The Wyandotte Herald, Kansa City, Kansas, 7 April 1898, “Air in Mammoth Cave“)

So, despite the fact that we can look back at the time before 1920, and see that there may have been an impact from the increased use of saltpeter on the general health of the German and Austrian population, and by extension, on the European population, such a link was probably not obvious.  The general view of saltpeter was favourable.


From the late 1800’s, scientists started to work out that the saltpeter was not the real curing agent, but its cousin, the far more toxic compound, nitrite (CodeCogsEqn (2)). It started to emerge that it has a more direct impact on curing than nitrate.  

Contrary to the generally positive view of saltpeter pre-1900’s, nitrite was viewed by the public in the most negative light.  Their view was not completely unfounded because it is estimated that nitrite is 10 times more toxic than nitrate, but what the general public did not understand was that nitrate became nitrite after a time and that the nitrate from their darling of all salts, sodium or potassium nitrate, turned into the villain, nitrite.

Scientists experimented from early on in its direct use in meat curing.  A private laboratory in Germany, founded in 1848 by C.R. Fresenius recorded, for example, experimented with sodium nitrite as curing agent.  (Concerning Chemical Synthesis and Food Additives)  THis is the earliest experiment I have been able to locate thus far where nitrite is used as a preservative in meat.

The Russian botanist and microbiologist, Sergei Nikolaievich Winogradsky (1856 – 1953) identified a class of bacteria which oxidizes ammonia (CodeCogsEqn (3).gif) or ammonium (CodeCogsEqn (4)) to nitrite (CodeCogsEqn (2)) and nitrite to nitrate (CodeCogsEqn (1)).  The process is called nitrification.

E. Meusel (1875) discovered another class of microorganisms living in soil and natural waters which reduce nitrates to nitrites and even further.  (Meusel, E. 1875)  It was found that in the absence of oxygen, these microbes use and thus reduces nitrates (CodeCogsEqn (1)) to nitrite (CodeCogsEqn (2)) in their metabolic processes.  In 1790 Antoine de Lavoisier (1743 – 1794) named the compound nitrite “as they are formed by nitric or by nitrous acid.”  (Lavoisier, A; 1965: 217)  Thus two different compounds exist with only a small change in the spelling namely nitrate and nitrite, indicating the fact that nitrite has one less oxygen atom compared to nitrate.  The loss of one oxygen atom, however, renders the molecule far more reactive, increasing its toxicity 10 times.

In 1891, Eduard Polenske, working for the Imperial Health Office, analysed cured meat for its nutritional value and noted that the nitrate in the curing brine and in the meat changed to nitrites.  He predictably and correctly speculated that this was due to microbial activity, identified by Meusel, 16 years earlier.  In his article, he predicted that his the expected reduction would cause an outcry.

Academic work continued uncovering a much closer relationship between the toxic nitrite and meat curing than the darling of the sciences, saltpeter.  The German scientist, Nothwang confirmed the presence of nitrite in curing brines in 1892.  In 1899, another German scientist, K. B. Lehmann confirmed that the cured colour was linked to nitrite and not saltpeter.  Yet another German hygienists, one of Lehmann’s assistant at the Institute of Hygiene in Würzburg,  Karl Kißkalt (1875 – 1962), confirmed Lehmann’s observations and showed that the same red colour resulted if the meat was left in saltpeter (potassium nitrate) for several days before it was cooked, thus confirming Polenske’s notion of bacterial reduction of nitrate to nitrite which finally cures the meat.  S. J. Haldane showed that nitrite is further reduced to nitric oxide (NO) in the presence of muscle myoglobin and forms iron-nitrosyl-myoglobin. It is nitrosylated myoglobin that gives cured meat, including bacon and hot dogs, their distinctive red colour and protects the meat from oxidation and spoiling.

The work of these scientists was enough evidence for the German government and in 1909, probably due to the negative views of the public towards nitrite, they legalised only the use of a partially reduced form of nitrates in curing mixes which were marketed across Europe.  (Bryan, N. S. et al, 2017: 86 – 90)

The Danish invention

The Danes applied their knowledge of bacterial reduction of nitrate to nitrite and developed a curing method where they reused brine that was “reduced” to nitrite already. They allowed fresh brine to be continually introduced into the system, bacterial reduction to take place and thus supplemented the nitrite concentration of the previously used brine.  This had the additional benefit of “seeding” new brine with just the right bacteria required for nitrite reduction.

According to this method they first injected fresh brine consisting of salt and saltpeter (potassium nitrate) into meat.  They then left the meat for several days in a cover brine. The cover brine was never changed and came to be known as the “mother brine.”  It was their source of nitrite that was directly applied to the curing process.  The mother brine was strained and boiled before it was re-used to eliminate pathogenic bacteria.

1910/ 1911

Clues to the date of the Danish invention come to us from newspaper reports about the only independent farmer-owned Pig Factory in Britain of that time, the St. Edmunds Bacon Factory Ltd. in Elmswell.  The factory was set up in 1911. According to the newspaper reports they learned and practiced what at first was known as the Danish method of curing bacon and later became known as tank-curing or Wiltshire cure.  A person was sent from the UK to Denmark in 1910 to learn the new Danish Method.  ( This Danish method involved the Danish cooperative method of pork production founded by Peter Bojsen on 14 July 1887 in Horsens.  The newspaper reports talked about a “new Danish” method.  The “new” aspect in 1910 and 1911 was undoubtedly the tank curing method.

Another account from England puts the Danish invention of tank curing early in the 1900’s.  C. & T. Harris from Wiltshire, UK, switched from dry curing to the Danish method during this time. In a private communication between myself and the curator of the Calne Heritage Centre, Susan Boddington, about John Bromham who started working in the Harris factory in 1920 and became assistant to the chief engineer, she writes: “John Bromham wrote his account around 1986, but as he started in the factory in 1920 his memory went back to a time not long after Harris had switched over to this wet cure.”

So, early in the 1900’s, probably sometime between 1899 and 1910, the Danes invented and practiced tank-curing which was brought to England around 1911 based on the work of the fathers of our current method of meat curing.

The German/ Austro-Hungarian invention

Where Denmark focused on harnessing the power of old brine, in Germany they were toying with the idea of using sodium nitrite as their source of nitrite.  Sodium nitrite was at this time used extensively in an intermediary step in the lucrative coal tar dye industry that flourished in Germany and in the Austrian-Hungarian empire, notably around the city of Prague.  There was a second use of sodium nitrite in medicine. It was expensive to produce and viewed with much skepticism by the general public for use in food on account of its high toxicity.  (Concerning the direct addition of nitrite to curing brine)

It was the First World War that provided the transition events that caused the sodium nitrite to end up being used as the source of nitrite in curing brines in Germany where its use in food was still illegal.  Saltpeter was reserved for the war effort being one of the main components used in manufacturing of gunpowder and was consequently no longer available as curing agent for meat during World War One. (Concerning the direct addition of nitrite to curing brine)


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

The first country to legalise the use of nitrite directly was the Austro-Hungarian Empire and in 1915.  At age 19, Ladislav Nachmüllner invents Praganda, the first legal commercial curing brine containing sodium nitrite in the city of Prague.  He says that he discovered the power of sodium nitrite through  “modern-day professional and scientific investigation.”  He probably actively sought an application of the work of Haldane. He quotes the exact discovery that Haldane was credited for in 1901 that nitrite interacts with the meat’s “haemoglobin, which changes to red nitro-oxy-haemoglobin.”  (The Naming of Prague Salt)


By 1917 nitrite was not only used for curing meat in Germany, but proprietary meat cures containing nitrites were being marketed across Europe.  (Concerning Chemical Synthesis and Food Additives)

Developments in the United States

Both these methods were being looked at very closely in the United States around this time.


The first recorded direct use of sodium nitrite as a curing agent in the USA was in a secret experiment in 1905.  The USDA approved its use as a food additive in 1906.  (Concerning the direct addition of nitrite to curing brine)


A court case was brought by the US Federal Government against the Mill and Elevator Company of Lexington, Nebraska.  The charge was that they adulterated and misbranded flour and sold it to a grocer in Castle, Missouri.  The case was brought by the government under the pure food and drug act of 1906.  (Chicago Daily Tribune ; 7 July 1910; Page 15) The government contended that “poisonous nitrites are produced in the flour by bleaching.”  This is one example of the gigantic controversy that raged around the world about the use of nitrites in food and the careful work that was done by the US government in the 1920, 30’s and onwards, was in the first place in dealing with the known high toxicity of nitrites.


In 1915, George F. Doran of Omaha, Nebraska, filed a patent for using “sterilized waste pickling liquor which he discovered contains soluble nitrites produced by conversion of the potassium nitrate, sodium nitrate, or other nitrate of the pickling liquor when fresh, into nitrites.  As such his patent involved taking waste pickling liquor from the cured meats.”  This is the same concept as tank curing invented in Denmark sometime before 1910 and probably after 1899. He states the objective of his invention as “to produce in a convenient and more rapid manner a complete cure of packing house meats; to increase the efficiency of the meat-curing art; to produce a milder cure; and to produce a better product from a physiological standpoint.” (US 1259376 A)

Despite the obvious advantage of a far quicker curing time of the use of sodium nitrite had over the tank cured Danish method, the fact that Doran still took the trouble to register the patent for a tank curing method in 1915 makes sense if one considers that tank-curing or the Wiltshire curing process became widespread in application in England.

The problem with the Danish and later, Engish system was, of course, shelf life due to the high microbial load from the mother brine and the uncontrolled nature of the process of nitrite formation (nitrite levels have been shown to range between 2 and 960 ppm in products cured using this method). (Bryan, N. S. et al, 2017: 86 – 90)


In 1923, the Bureau of Animal Industry commissioned a study to investigate the direct addition of nitrite for meat curing.  Kerr, et al, under the supervision of inspectors from the Bureau of Animal Industry, cured hams with approximately 2000 ppm nitrite in the curing mix.  The first issue they investigated was to compare nitrite curing with nitrate curing from the standpoint of organoleptic equivalence and if excess amounts of nitrite are required for nitrite curing.

They also looked at the amount of nitrite that was left in the meat after sufficient curing took place, thus introducing the concept of residual nitrite.  These they compared with the amount of nitrite that was in the curing brine.  The question was how much nitrite is required to cure meat.  It was known that nitrite is a more powerful toxin than nitrate; it was further known that using nitrate instead of nitrite caused inconsistent nitrite levels in the curing brine and in the meat.  By understanding the amount of nitrites that typically react in the meat to form nitric oxide and to cure the meat and by taking that as the limit of nitrite that can be added directly, one, therefore, minimises the risk of having consumers ingest nitrites.


By 1925 a document was prepared by the Chicago based organisation, The Institute of American Meat Packers and published in December of this year.  The Institute started as an alignment of the meat packing companies set up by Phil Armour, Gustavus Swift, Nelson Morris, Michael Cudahy, Jacob Dold and others with the University of Chicago.  (Concerning the direct addition of nitrite to curing brine)

A newspaper article about the Institute sets its goal, apart from educating meat industry professionals and new recruits, “to find out how to reduce steers to beef and hogs to pork in the quickest, most economical and the most serviceable manner.”   (The Indiana Gazette.  28 March 1924).  In this statement is the clue to the reason of its dominance in the United States where bigger, better and faster was the call to arms for the new world’s industries.

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

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

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


The 1926 study by Kerr and co-workers, was done long before there was any link established between nitrite and the formation of cancer-causing substances upon frying and ingestion.  This only emerged in the ’70’s.  In 1926, the work was based on the general knowledge of nitrite’s toxicity and the publics very negative perceptions about it.  In the report, they state that public health was the primary motivation behind the study.  (Kerr, et al, 1926 : 543)  The test was a step in the right direction – towards defining and limiting residual nitrite.

I quote from their report.  “The first experiment involving the direct use of nitrite was formally authorized January 19, 1923, as a result of an application by one of the large establishments operating under Federal meat inspection. Before that time other requests for permission to experiment with nitrite had been received but had not been granted. The authorization for the first experiment specified that the whole process was to be conducted under the supervision of bureau inspectors and that after the curing had been completed the meat was to be held subject to laboratory examination and final judgment and would be destroyed if found to contain an excessive quantity of nitrites or if in any way it was unwholesome or unfit for food. This principle was rigidly adhered to throughout the experimental period, no meat being passed for food until its freedom from excessive nitrites had been assured, either by laboratory examination or through definite knowledge from previous examinations, that the amount of nitrite used in the process would not lead to the presence of an excessive quantity of nitrites in the meat. By “excessive^ is meant a quantity of nitrite materially in excess of that which may be expected to be present in similar meats cured by the usual process.”  (Kerr, et al, 1926 : 543)

An interesting side note is the fact that this fixes the date of the first official experiment using nitrites ever conducted in the United States.  There can be little doubt that the large packing plants in Chicago used nitrites directly in meat curing, long before this, at least from 1918, following World War 1.  I have even received reports of the first unofficial experiment of this nature that was done in 1905, presumably also in Chicago.  (Concerning the direct addition of nitrite to curing brine)  The large establishment who applied for the permit would have been one of the following list of packers, the Armour Packing operation, Morris & Company, Cudahy Packing Company, Wilson Packing Plant or Swift Packing.  These four companies, at the time, were some of the largest and most powerful corporations on earth.

The maximum nitrite content of any part of any nitrite-cured ham [was found to be] 200 parts per million. The hams cured with nitrate in the parallel experiment showed a maximum nitrite content of 45 parts per million.”  (Kerr, et al, 1926 : 543) The conclusion was that “hams and bacon could be successfully cured with sodium nitrite, and that nitrite curing need not involve the presence of as large quantities of nitrite in the product as sometimes are found in nitrate- cured meats.”  (Kerr, et al, 1926 : 545)

Related to the health concerns, the report concluded the following:

  1. The presence of nitrites in cured meats, was already sanctioned by the authoritative interpretation of the meat inspection and pure food and drugs acts sanctioning the use of saltpeter; as shown previously, meats cured with saltpeter and sodium nitrate regularly contain nitrites. (Wiley, H, et al, 1907) (Kerr, et al, 1926 : 550)
  2. The residual nitrites found in the nitrite-cured meats were less than are commonly present in nitrate-cured meats.  The maximum quantity of nitrite found in nitrite-cured meats, in particular, was much smaller than the maximum resulting from the use of nitrate.  (Kerr, et al, 1926 : 550)
  3. The nitrite-cured meats were also free from the residual nitrate which is commonly present in nitrate-cured meats.  (Kerr, et al, 1926 : 550)
  4. On the contrary, the more accurate control of the amount of “nitrite and the elimination of the residual or unconverted nitrate are definite advantages attained by the substitution.  (Kerr, et al, 1926 : 550)

Following further studies, the Bureau set the legal limit for nitrites in finished products at 200 parts per million.  (Bryan, N. S. et al, 2017: 86 – 90)

Conventional wisdom that surfaced in the 1920’s suggested that nitrate and nitrate should continue to be used in combination in curing brines  (Davidson, M. P. et al; 2005:  171) as was the case with the Danish curing method and the mother brine concept of the previous century.  Nitrite gives the immediate quick cure and nitrate acts as a reservoir for future nitrite and therefore prolongs the supply of nitrite and ensures a longer curing action.  This concept remained with the curing industry until the matter of N-nitrosamines came up in the 1960’s and 70’s, but remarkably enough, it still persists in places like South Africa where to this day, using the two in combination is allowed for bacon.


The USDA progressed the ruling on nitrate and nitrites further in 1931 by stating that where both nitrites and nitrates are used, the limit for nitrite is 156 ppm nitrite and 1716 nitrate per 100lb of pumped, cured meat.  (Bryan, N. S. et al, 2017: 86 – 90)

1960’s – N-Nitrosamine

Up to the 1960’s the limit on the ingoing level of nitrites was based on its toxicity.  In the late 1950’s an incident occurred in Norway involving fish meal that would become a health scare rivaled by few in the past.  1960’s researchers noticed that domestic animals fed on a fodder containing fish meal prepared from nitrite preserved herring were dying from liver failure.  Researchers identified a group of compounds called nitrosamines which formed by a chemical reaction between the naturally occurring amines in the fish and sodium nitrite.  Nitrosamines are potent cancer causing agents and their potential presence in human foods became an immediate worry.  An examination of a wide variety of foods treated with nitrites revealed that nitrosamines could indeed form under certain conditions.  Fried bacon, especially when “done to a crisp,” consistently showed the presence of these compounds.  (Schwarcz, J)  In bacon, the issue is not nitrates, but the nitrites which form N-nitrosamines.

This fundamentally sharpened the focus of the work of Kerr and co-workers of the 1920’s in response to the general toxicity of nitrites to the specific issue of N-nitrosamine formation.  Reviews from 1986 and 1991 reported that “90% of the more than 300 N-nitroso compounds that have been tested in animal species including higher primates causes cancer, but no known case of human cancer has ever been shown to result from exposure to N-nitroso compounds.”  However, despite this, there is an overwhelming body of indirect evidence that shows that a link exists and “the presence of N-nitroso compounds in food is regarded as an etiological risk factor.   It has been suggested that 35% of all cancers in humans are dietary related and this fact should not surprise us.  (Pegg and Shahidi, 2000)

Studies have been done showing that children who eat more than 12 nitrite-cured hot dogs per month have an increased risk of developing childhood leukemia.  The scientists responsible for the findings themselves cautioned that their findings are preliminary and that much more studies must be done.  It may nevertheless be a good approach for parents to reduce their own intake of such products along with that of their children in cases where intake is high.  (Pegg and Shahidi, 2000)

These studies must be balanced by the fact that an overwhelming amount of data has been emerging since the 1980’s that indicate that N-nitroso compounds are formed in the human body.  What is important is that we keep on doing further research on N-nitrosamines and the possible link to cancer in humans.  Not enough evidence exists to draw final conclusions.

1970 – The response to the N-Nitrosamine scare.

Back to the 1970’s, so grave was the concern of the US Government about the issue that in the early 1970’s they seriously considered a total ban on the use of nitrites in foods. (Pegg and Sahidi, 2000)  The response to the N-nitrosamine issue was to go back to the approach that was implemented following the work of Kerr and co-workers in 1926.

The first response was to eliminate nitrate from almost all curing applications.  The reason for this is to ensure greater control over the curing.  Meat processors continued to use nitrate in their curing brines after 1920 until the 1970’s.  One survey from 1930 reported that 54% of curers in the US still used nitrate in their curing operations.  17% used sodium nitrite and 30% used a combination of nitrate and nitrite.  By 1970, 50% of meat processors still used nitrate in canned, shelf-stable.  In 1974 all processors surveyed discontinued the use of nitrates in these products including in bacon, hams, canned sterile meats, and frankfurters.  One of the reasons given for this change is the concern that nitrate is a precursor for N-nitrosamine formation during processing and after consumption.  (Bryan, N. S. et al, 2017: 86 – 90)

The reason for the omission in bacon, in particular, is exactly the fact that the nitrates will, over time continue to be converted to nitrites which will result in continued higher levels of residual nitrites in the bacon compared to if only nitrite is used.  The N-nitrosamine formation from nitrites is a reaction that can happen in the bacon during frying or in the stomach after it has been ingested.  It will not happen from the more stable nitrates.

It has been discovered that nitrate continues to be present in cured meats.  Just as the view that if nitrate was added, no nitrite is present in the brine as was the thinking in the time before the early and mid-1800’s, in exactly the same way it is wrong to think that by adding nitrite only to meat, that no nitrate is present.  “Moller (1971) found that approximately 20% of the nitrite added to a beef product was converted to nitrate within 2 hours of processing.  Nitrate formation was noted during incubation before thermal processing, whereas after cooking only slight nitrate formation was detected.  Upon storage, the conversion of nitrite to nitrate continued.  Herring (1973) found a conspicuous level of nitrate in bacon formulated only from nitrite.  As greater concentrations of nitrite were added to the belly, a higher content of nitrate was detected in the finished product.  They reported that 30% of the nitrite added to bacon was converted to nitrate in less than one week and the level of nitrate continued to increase to approximately 40% of the added nitrite until about 10 weeks of storage.  Moller (1974) suggested that when nitrite is added to meat, a simultaneous oxidation of nitrite to nitrate and the ferrous ion of CodeCogsEqn (5)  to the ferric ion of metMb occurs.” Adding ascorbate or erythorbate plays a key role in this conversion.  (Pegg and Shahidi, 2000)  The issue is not the nitrate itself, but the uncontrolled curing that results from nitrate and the higher residual nitrites.

Secondly, the levels of ingoing nitrite were reduced, especially for bacon.  The efficacy of these measures stems from the fact that the rate of N-nitrosamine formation depends on the square of the concentration of residual nitrites in meats and by reducing the ingoing nitrite, the residual nitrite is automatically reduced and therefore the amount of N-nitrosamines.  (Pegg and Sahidi, 2000)  Legal limits were updated in 1970 in response to the nitrosamine paranoia.  A problem with this approach is however that no matter by how much the ingoing nitrite is reduced, the precursors of N-Nitrosamine still remains in the meat being nitrites, amines, and amino acids.

An N-nitrosamine blocking agent was introduced in the form of sodium ascorbate or erythorbate. “There are several scavengers of nitrite which aid in suppressing N-nitrosation; ascorbic acid, sodium ascorbate and erythorbate have been the preferred compound to date.  Ascorbic acid inhibits N-Nitrosamine formation by reducing CodeCogsEqn (11)  to give dehydroascorbic acid and NO.  Because ascorbic acid competes with amines forCodeCogsEqn (11), N-Nitrosamine formation is reduced.  Ascorbate reacts with nitrite 240 times more rapidly than ascorbic acid and is, therefore, the preferred candidate of the two.  (Pegg and Sahidi, 2000)

More detailed studies identified the following factors to influence the level of N-nitrosamine formation in cured meats.  Residual and ingoing nitrite levels, preprocessing procedure and conditions, smoking, method of cooking, temperature and time, lean-to-adipose tissue ratio and the presence of catalyst and/ or inhibitors.  It must be noted that in general, levels of N-nitrosamines formation has been minuscule small, in the billions of parts per million and sporadic.  The one recurring problem item remained fried bacon.  In its raw state bacon is generally free from N-nitrosamines “but after high-heat frying, N-nitrosamines are found almost invariably.”  One report found that “all fried bacon samples and cooked-out bacon fats analyzed” were positive for N-nitrosamines although at reduced levels from earlier studies.  (Pegg and Sahidi, 2000)

Regulatory efforts since 1920 have shown a marked decrease in the level of N-nitrosamines in cured meats, even though it is still not possible to eliminate it completely.  “Cassens (1995) reported a marked decrease (approx 80%) in residual nitrite levels in of US prepared cured meat products from those determined 20 years earlier; levels in current retail products were 7 mg/kg from bacon.”  This and similar results have been attributed to lower nitrite addition levels and the increased use of ascorbate or erythorbate.  (Pegg and Sahidi, 2000)

Current USA regulations and tightening the measures from the 1970’s.

Nitrite can be used in foods and nitrate, very selectively based on the product category and the method of curing.  Immersion cured, massaged or pumped products (example hams or pastrami) – maximum ingoing level of 200 ppm sodium or potassium nitrite and/ or 700 ppm nitrate based on raw product weight.  (Bryan, N. S. et al, 2017: 86 – 90)

Dry cured products – a maximum of 625 ppm ingoing nitrite, and/ or 2187 ppm nitrate since the products have long curing times that result in immediate nitrite reaction with myoglobin and longer term conversion of nitrate to nitrite.  (Bryan, N. S. et al, 2017: 86 – 90)

Comminuted products such as Frankfurters, Bologna, and other cured sausages – maximum ingoing nitrite level of 156 ppm sodium or potassium nitrite based on raw meat block.  Nitrite can be added to all these at a rate of 1718 ppm regardless of salt used.  (Bryan, N. S. et al, 2017: 86 – 90)

1978 bacon levels – USA

Inoing nitrite levels were reduced in 1978 and a required limit was set for ascorbate.  It was also explicitly ruled that nitrate may not be used in bacon production.

-Maximum ingoing level of sodium nitrite – 120 ppm

-Maximum ingoing level of potassium nitrite – 148 ppm

-547 ppm ascorbate or erythorbate must be added.

(Bryan, N. S. et al, 2017: 86 – 90)


In the USA, in 1980, the National Acadamy of Sciences (NSA) entered into a contract with the USDA and FDA.  They established the Committee on Nitrate and Alternative Curing Agents in Food.  The brief of the committee was to investigate the health risk associated with the overall exposure to nitrate, nitrite and N-nitroso compounds.  They published a report, “The Health Effects of Nitrite and N-nitroso Compounds.”

They found nitrate not to be carcinogenic or mutagenic.  It was found that certain populations showed an association of an exposure to high nitrate levels and certain cancers.  More studies are required.

Nitrite was similarly found not to act directly as a carcinogen in animal studies and more studies are necessary.

The committee recognised the use of nitrite as an effective barrier against foodborne botulism, thus validating the continued use of nitrites in meat curing.  They also put the overall risk in perspective by estimating the lifetime risk of cancer from cured meats to be one in a million if “humans were exposed to a daily dose of 5.8 to 19 ng of nitrosodimethylamine per ki~ogram of body weight or 0.85 to 2. 7 ng of nitrosodimet~lamine per em of body surface. In arriving at this estimate, the committee has also assumed that (1) the dietary doses given to rats can be converted to unit of dose per unit of body weight or per unit of body surface area to reflect human exposure and (2) that nitrosodimethylamine is the main source of exposure to nitrosamine& for humans and is, therefore, representative of all nitrosamine&, even though its potency in animals is greater than that of many other nitrosamine.”

The committee also examined seven pothetical population groups and estimated that the lifetime risk of cancer from exposure to all sources of nitrosamines would be 820 to 18,000 per million for a high risk group (including occupational exposure), 11 to 250 in a million for a high cured meat diet group, 8 to 180 in a million for an average population of nonsmokers, and 3 to 74 in a million for a low risk group.”

A specific recommendation, relevant to the question of the use of nitrates in curing brines is that the use of nitrates in curing systems should be eliminated with the exception of products where a long curing time is required.  The reason is that nitrate and nitrates can have acute toxic effects and contribute to the formation of N-nitrose compounds.

Despite all this, the committee found that the prudent approach is to continue to use nitrite as a proven and effective hurdle to prevent the outgrowth of Clostridium Botulinum spores and the accompanying toxin formation.  It is in the publics interest to assume that temperature and other product abuses will take place and using nitrite as a hurdle remains a reasonable measure.

Here is the pdf copy of the entire report:  The Health Effects of Nitrite and N-nitroso Compounds

New 1986 bacon levels – USA – testing the limits of the system

The general trend of reducing residual nitrate and limiting N-nitrosamine formation continued.  The danger, however, exists that ingoing nitrite levels may be reduced so dramatically as to compromise its function as a barrier against botulism.  The danger of nitrites and its benefits must always be held in balance.

-Skinless bacon – the requirements were kept at the 1978 levels, but it was explicitly emphasised that these ruling applies in order to reduce the possibility of N-nitrosamine formation.  A practical measure was introduced which allows for an approximately 20% variance is allowed from the ingoing nitrite on injection or massaging (96-144 ppm).

In order to ensure efficacy against pathogens, sodium nitrite can be reduced to 100 ppm (123 ppm potassium nitrite) with “appropriate partial quality control program.”  If sugar and a starter culture are added to the brine, 40 – 80 ppm sodium nitrite (49 – 99 potassium nitrite).

Dry cured bacon – the limit was set at 200 ppm nitrite or 246 potassium nitrite.

(Bryan, N. S. et al, 2017: 86 – 90)

EU Rules, Directive 95/2/EC, modified in Directive 2006/52/EC

Maximum ingoing level of bacon is 150 ppm nitrite; max residue level at between 50 and 175 ppm. (in Denmark, this limit is lower at 60 – 150 ppm for semi preserved products and special cured hams).  (Bryan, N. S. et al, 2017: 86 – 90)

Canadian Regulations Bacon

120 ppm and it is stated that this level is set in order to prevent N-Nitrosamine formation.  (Bryan, N. S. et al, 2017: 86 – 90)

South African Regulations

The South African max allowed limits on nitrite, nitrate and ascorbate or erythorbate are:

from Regulation R965 of 1977(18):

– Potassium and sodium nitrate:  200mg/ kg
– Potassium or sodium nitrite: 160mg/kg

Where nitrate and nitrite are used in combination they must be added together and proportionally neither one can exceed the max limit (section 2b of Regulation R965 of 1977).

For using erythrobic acid or sodium erythrobate:  550 mg/kg
L Ascorbic Acid:  550 mg/kg.


The continued use of nitrite is undoubtedly valid in the face of its efficacy against serious foodborne pathogens.  It is, however, important to take every precaution possible to mitigate the risk posed by N-nitrosamines, including limiting the maximum allowed addition of nitrite to curing brines, limiting residual nitrite, controlling the curing by using nitrites and not nitrates in bacon and the addition of correct levels of ascorbate or erythorbate.  The fact that nitrates are still allowed with nitrites in curing brines in South Africa is a matter of concern.

Objections are two fold.  On the one hand, it increases the residual nitrites (over time, nitrites continue to be formed from nitrates through bacterial reduction) increasing the amount of nitrites present during frying and ingested which can form N-nitrosamines in the stomach.  Another issue is that the exact dosage of nitrites is not left, in part, to the action of bacteria and I fail to see the point behind this.  The thinking about nitrates acting as a reservoir for continued nitrite production in order to maximise its antimicrobial efficacy becomes an irrelevant point in light of the danger of N-nitrosamine formation from the higher residual nitrites and the thinking which stems from the 1920’s has been altered around the world with good reason and yielding good results.

An equally serious problem may be that the South African regulations do not make the use of ascorbate or erythorbate mandatory nor does it set minimum required levels.  It will be interesting to do a study of the residual nitrite levels in South African bacon over time.  Much work remains.

After I did the article, it occurred to me that if I would cut out cured meat from my diet altogether in order to prevent even the smallest chance of exposure to N-nitrosamines and if I would subject the rest of my diet to the same rigor applied to the issue of nitrites, it may very well be found that I was better off eating the processed foods in comparison with what I may consume in its place.  As a whole, it is possible that consuming processed foods along with regular exercises places me in a better position health wise than cutting out these foods from my diet altogether and no exercise.  This issue must be seen in context.  This is a fact that researchers regularly point to when they publish date on the health effects of nitrite.  I can only echo the prevailing sentiment on the subject – that much more research needs to be done.

Few issues received more comprehensive treatment than the matter of N-nitrosamine formation since the early 70’s and an unfathomable amount of excellent literature exists on the subject.  I write these articles in order to learn.  Like the issue of meat curing itself, the matter at hand is very complex.


Bryan, N. S. and Loscalzo, J. (Editors) 2017.  Nitrite and Nitrate in Human Health and Disease.  Springer International Publishing.  Chapter by J. T. Keeton.

Frances, M. P. (Editor) et al..  1981.  The Health Effects of Nitrate, Nitrite, and N- Nitroso Compounds.  National Academic Press. (

KERR, R. H., MARSH, C. T. N., SCHROEDER, W. F., and BOYER, E. A..  1926.   Associate Chemists, Bureau of Animal Industry, United States Department of Agriculture.  THE USE OF SODIUM NITRITE IN THE CURING OF MEAT.  Journal of Agricultural Research Vol. 33, No. 6.  Sept. 15, 1926 Key No. A-112.  Washington, D. C.

Lauer K. 1991.  The history of nitrite in human nutrition: a contribution from German cookery books.  Journal of clinical epidemiology. 1991;44(3):261-4.

Lavoisier, A.  1965.  Elements of Chemistry.  Dover Publications, Inc.  A republication of a 1790 publication

Morton, I. D. and Lenges. J.  1992.  Education and Training in Food Science: A Changing Scene.  Ellis Hornwood Limited.

Schwarcz, J

WILEY, H. W., DUNLAP, F. L., and MCCABE, G. P. 1907. DYES, CHEMICALS, AND PRESERVATIVES IN FOODS. U. S. Dept. Agr., Off. Sec. Food Insp. Decis. 76, 13 p.

The Wyandott Herald, Kansa City, Kansas, 7 April 1898, “Air in Mammoth Cave

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