Bacon Curing – a historical review

Introduction to Bacon & the Art of Living

The story of bacon is set in the late 1800s and early 1900s when most of the important developments in bacon took place. The plotline takes place in the 2000s with each character referring to a real person and actual events. The theme is a kind of “steampunk” where modern mannerisms, speech, clothes and practices are superimposed on a historical setting.  Modern people interact with old historical figures with all the historical and cultural bias that goes with this.


Meat Curing – A Review
Cape Town, November 1959

Dear Lauren,

Over the years I covered the progression of both curing techniques and the understanding of how curing takes place in great detail. There is a need with so much information given, to summarise everything to enable you to have a birds-eye view of the progressions. If you have a good grasp of both the process and the development of the various curing systems you will be well on your way to become a good meat curer yourself.

I, therefore, set out to give a historical overview of the development of meat curing. This review spans many millennia. From the dawn of humanity to our current time where we touch on modern developments in meat curing technology. Curing started out as a way of managing food scarcity by providing a means of fortifying meat against spoilage and over time became a culinary craft. This review is done from the perspective of a commercial high throughput bacon plant and not from the viewpoint of artisan curing operations, some of which is itself large and service an expansive client base. These operations are, however, almost exclusively restricted to developed countries. It must also be said that what was yesterdays most advanced and quickest way of producing bacon became today’s artisan curing techniques.

The Curing Process

A modern understanding of the benefits of curing is that it fixes a pinkish-reddish cured meat colour. It endows the meat with unique longevity, even if left outside a refrigerator, many times longer than that of fresh meat. It is powerful enough to prevent the deadly toxin formation by Clostridium botulinum. It prevents the formation of rancidity in fat. It lastly gives meat a unique cured taste.

What is completely mesmerising in meat curing is that the basic process follows physiological processes, essential for human life. The fact that humans stuck, as it were, to the evolutionary playbook in its practice of curing in that it mimics these physiological processes to the smallest details is completely astounding! I will write to you separately about how the basic processes in curing are exactly the processes essential for life that happens every moment in our bodies! Far from a villain that causes health trouble, nitrate, nitrite and nitric oxide are indispensable molecules to life on earth. Of course, its overuse, in proportions greater than what nature dictates, is extremely unhealthy, as we discussed in Chapter 12.06: Regulations of Nitrate and Nitrite post-1920’s: the problem of residual nitrite. By and large, meat curing is a safe and essential technique of preserving meat.

Discovering the mechanics behind meat curing was a slow process that took hundreds of years. (For an overview of some of the people behind the most important discoveries, see Fathers of Meat Curing)  A survey of farm curing methods conducted in 1951 by the US Department of Agriculture among farmers in the US revealed the following brining methods used:

  • Dry cure – no pumping,
  • Brine cure – no pumping (the use of cover brine),
  • Brine cure – pumped, and
  • Dry cure – pumped.  (Dunker and Hankins; 1951: 4)

We can add the following to this list from 1951:

  • Sweet Curing (Stitch Pumping with dry curing and with hot smoking)
  • Mild Curing (the re-use of cover brine with or without stitch pumping, with or without dry salting)
  • Pale Dry Bacon (Sweet curing with no smoking, only drying)
  • The direct use of nitrites in curing brines
  • Grid or Formed Bacon

For a discussion on the mechanics of curing, please review the letter I sent you previously Chapter 12.09: The Curing Reaction.

Salt Only (Dry cure – no pumping – salt only – using a dry rub or brine)

Exactly where salt curing of meat started is an interesting question. There is ample evidence that salt preservation of meat was done from the earliest of times. Despite the fact that there are records of fish being salt-cured in China going back to 2000 BCE and from Egypt and Mesopotamia, the practice is much older.

Ancients consumed their food raw before it was discovered how to make fire. (How did Ancient Humans Preserve Food?) Even after fire-making was invented and this technology became universally part of human culture, humans only cooked their food intermittently for a very long time. There are cultures to this day that eat raw meat in one form or the other. Besides this, hanging meat to dry in the sun, the wind or over a fireplace without adding any curing agent such as salt was practised in southern Africa, North America, and Nepal, to mention just a few places that I am personally aware of. It was likely universally practised at some point in the past. 

Salt was without question the first curing agent and in all likelihood, salt in the form of seawater. It seems that as people migrated from coastal regions, inland, they developed solar evaporation to extract the salt from seawater along with techniques such as boiling the water off when it became more difficult to access seawater when communities started to settle further away from the coast. It is often claimed that salt did not play a significant role in southern Africa. Nothing could be further from the truth! After a careful investigation of the use of salt for meat preservation in southern Africa, the evidence points to the fact that the power of salt to preserve meat was known by for example the Khoe and the San people, but they preferred to simply hang meat in the sun and the wind to dry. Still, salt played a significant role in the diets of ordinary people. They understood it and used it!  (Salt and the Ancient People of Southern Africa) A direct link can be made to every great civilisation that existed in antiquity in the fact that they all knew the value and uses of salt.

China

One of the greatest and oldest civilisations that ever existed (and still exist) is the Chinese! What we know for sure is that salt curing of meat occurred in China from very early on. Flad, et al. (2005) showed that salt production was taking place in China on an industrial scale as early as the first millennium BCE at Zhongba. “Zhongba is located in the Zhong Xian County, Chongqing Municipality, approximately 200km down-river along the Yangzi from Chongqing City in central China. Researchers concluded that “the homogeneity of the ceramic assemblage” found at this site “suggests that salt production may already have been significant in this area throughout the second millennium B.C..” Significantly, “the Zhongba data represent the oldest confirmed example of pottery-based salt production yet found in China.”  (Flad, et al.; 2005)

Salt-cured Chinese hams have been in production since the Tang Dynasty (618-907AD). First records appeared in the book Supplement to Chinese Materia Medica by Tang Dynasty doctor Chen Zangqi, who claimed ham from Jinhua was the best. Pork legs were commonly salted by soldiers in Jinhua to take on long journeys during wartime, and it was imperial scholar Zong Ze who introduced it to Song Dynasty Emperor Gaozong. Gaozong was so enamoured with the ham’s intense flavour and red colour he named it huo tui, or ‘fire leg’. (SBS) An earlier record of ham than Jinhua-ham is Anfu ham from the Qin dynasty (221 to 206 BCE).

In the middle ages, Marco Polo is said to have encountered salt curing of hams in China on his presumed 13th-century trip. Impressed with the culture and customs he saw, he claims that he returned to Venice with Chinese porcelain, paper money, spices, and silks to introduce to his home country. Polo alleges that it was from his time in Jinhua, a city in eastern Zheijiang province, where he found salt-cured ham. Marco Polo is a controversial figure in that there is great uncertainty if he ever actually undertook the voyages he wrote about. Still, these stories, either first hand from Polo or from someone else who compiled it, the reports certainly had a basis in reality.

The reach of Chinese technology of salt production was impressive. On a trip to New Zealand, I learned that the Māori never developed salt extraction in any form. I did a short review of the colonization of Indonesia and salt extraction technology in an article, “Concerning the lack of salt industry in pre-European New Zealand and other tales from Polynesia and the region.” A brief survey of the history of salt extraction from Fiji, Samoa, New Guinea, Vanuatu, and Taiwan shows the large influence of China on regional salt production technology.

This study also revealed a possible forerunner of more formal salt production around the world, including in China. One of the earliest ways that salt found itself in food preparations was undoubtedly through the fact that seafood was consumed that naturally had added salt which came from the water. Another way would have been if meat was stored in seawater. Immersing carcasses of animals and fish in water would have been one of the earliest forms of preservation and since earliest communities gravitated to coastal regions, salt water would have been used and in addition to seafood which is rich in salt, it would have entered early human culture when food was cooked in seawater. It is likely that carcasses were stored in water at first to hide them from predators and its preserving power would soon have been discovered. Migrating groups would have noticed how seawater preserved meat better and changed (improved) the taste of the meat.

Polynesia

The study of salt in Polynesia shows that as groups migrated inland, away from the sea, saltwater was boiled to evaporate the water and leave the salt as a very basic salt extraction technique. The salt was then traded with the inland communities. This was widely practised in Taiwan until fairly recently. The references of it in Polynesia and Asia offer a suggested progression of the extraction of salt from seawater. Studies from Fiji identified population size, even of coastal communities to be a key driver of salt extraction technology. 

It seems that migrants from Taiwan spread their technology throughout the lands of Polynesia. Every evaluation of salt on the islands I looked at supports this. China would undoubtedly have been a key driver in the region in progressing salt extraction technology with Pappa New Guinea playing a large role where a multitude of techniques to extract salt was (and still is) in use. Solar evaporation of seawater, extracting salt through plant material and burning plants, naturally high in salt are a few of the developments from the region, which all presumably have their roots in the practice of simply boiling seawater; in turn, this was probably a progression of the practice of cooking food in seawater; which, in turn, had its roots in storing meat in saline solutions; which had its roots in simply immersing carcasses in bodies of water for storage. When we are at this point, we are clearly at the very early age of the existence of cognitive modern humans who were cognitively similar to modern humans.

New Zealand

In a discussion with a curator from the Canterbury Museum about the matter of salt production and trade in salt being absent from New Zealand’s ancient history, he drew my attention to the interesting practice of the Maori to slow boil large quantities of shellfish in freshwater. Had they not done so, it would not have been possible to consume large quantities at a time. There seems to be evidence that they did, in fact, consume large quantities of this at a time. It supports the notion that they knew about salt and the possibility exists that this was true across the world from very early. Like the people of southern Africa, people probably knew at least some of the techniques for extracting it, but some local populations, as was the case in New Zealand and many of the southern African populations, may have opted not to use the technology simply because it was not necessary. In the case of the Maori, they definitely knew to remove some of the salt from shellfish before consuming it. They have a word for salt which shows that they definitely knew about its taste. In southern Africa, most would have gotten their salt from meat or milk and when they could only eat plant material, they knew that a bit of salt would cure the ailments which resulted from a lack of salt.

Salt as a condiment

One can not talk about salt curing and not at least make mention of its use as a condiment. Even though too much salt alters the taste negatively, preservation through salt and altering (enhancing) the taste go hand in hand. Evidence is emerging about the use of condiments in food, the earliest discovery so far which dates in Europe going back 6000 years ago in Germany and Denmark. Archaeology magazine (Nov/ Dec 2013) reports that “a team of researchers has found phytoliths, small bits of silica that form in the tissues of some plants, from garlic mustard seeds, which carry strong, peppery flavour but little nutritional value. Because they were found alongside residues of meat and fish, the seed remnants represent the earliest known direct evidence of spicing in European cuisine. According to researcher Hayley Saul of the University of York, “It certainly contributes important information about the prehistoric roots of this practice, which eventually culminated in globally significant processes and events.” (Archeology)  Salt would undoubtedly have been part of their arsenal of taste enhancers.

It seems that our relationship with salt has never been static and to this day, it continues to evolve. More importantly, the discoveries in Denmark and Germany brings into focus innovations in the European lands of Germany, Austria, Hungary, the Czech Republic, Switzerland, Denmark, Holland, Belgium, Spain, France, and Poland. Besides these, there is Irland. What was happening in these regions while cities and kingdoms covering Mesopotamia, India, Pakistan, Nepal were developing salt industries and very sophisticated meat curing technologies based on salt, nitrate, and sal ammoniac? I am filling in the gaps over the years to come.

Origins of Nitrate/ Nitrite curing?

This study of salt also brings me back to my work on nitrite/ nitrate curing which has been a major focus for me over many years. While people living in desert areas would have discovered that certain salts have the ability to change the colour of meat from brown, back to pinkish/ reddish, along with increased preservation power and a slightly distinct taste, coastal dwellers would have observed the same. They would have noticed that sea salt or bay salt have the same ability.

Dr Francois Mellett, the renowned South African food scientist, sent me the following very interesting theory about the earliest discovery of the curing process in private communication between us on the matter. He wrote, “I have a theory that curing started even earlier by early seafarers: when a protein is placed in seawater, the surface amino acids are de-aminated to form nitrite for a period of 4 to 6 weeks. Nitrite is then converted to nitrate over the next 4 weeks. Finally, ammonia and ammoniac are formed from nitrate. It is possible that they preserved meat in seawater barrels and that the whole process of curing was discovered accidentally.”

I think he is on the right track. I suspect that people discovered this even long before barrels were invented. The use of seawater for meat storage and further preparation was so widespread that it would have been impossible not to have noticed meat curing taking place. If it is generally true that the earliest humans first settled around coastal locations before migrating inland, and if the seaside communities first noticed curing, it would push the discovery of curing many thousands of years earlier than we ever imagined, to a time when modern humans started spreading around the globe. When did it develop into an art or a trade is another question altogether, but I think we can safely push this back to the earliest cognitive and cultured humans whom we would have recognized as thinking “like us” if we could travel back in time and meet them.

We know that dry-curing of pork takes around 5 to 6 weeks under the right conditions and if the meat is not cut too thick. It must be cool enough that the meat doesn’t spoil before it is cured.  Even though I now suspect that curing was first noticed by communities living by the sea as I just explained, I suspect that curing salts in deserts were discovered since natural salts always appear as a mix of various salts and under certain conditions, these salt deposits contain small amounts of nitrate salts and ammonium chloride. This would have aided its development into an art by the much larger availability of nitrate and related salts.

I deal with these salts below under separate headings, but the most important two curing salts that appear to us from antiquity are saltpetre (sodium nitrate) and sal ammoniac (ammonium chloride).  Both salts were well known in Mesopotamia and references to them appear alongside references to salt curing of fish mentioned earlier and both salts were used in meat curing.

The ancients developed basic techniques of separating out the different salts. In particular, sal ammoniac was by far the more important salt of the bronze age (2000 BCE). It was produced in Egypt and mined in Asia where it occurs naturally. There are features of sal ammoniac that favour it as a salt for people who had a motivation to exploit new lands due to population pressure and climate changes or just curiosity. When the horse was domesticated around 5000 BCE, a food source was needed to sustain humans on long expeditions and I believe sal ammoniac fits the requirement perfectly.

Both salts cure the meat in a week which obviously had huge advantages over salt-only curing. This, I speculate, was the first incentive to change to a dedicated curing salt. Secondly, sal ammoniac, as far as I can find, was globally traded from much earlier on than saltpetre. Ancient Macedonian records indicate that even 2000BCE saltpetre was preferred in food over sal ammoniac on account of the better taste of saltpetre.

There is a modern era example of a curing technique that was good for a time and was then replaced with more agreeable methods as soon as supply lines were established. This technique, I believe actually existed from very early after the horse was domesticated and was re-introduced by various cultures, at various times. One such culture was the Boers who left the Cape Colony and moved into the interior of South Africa. The technique they used to cure their meat disappeared as soon as conventional supply lines were established.

The technique is curing of meat by hanging it over the neck of the horse or placing it under your saddle so that the sweat of the horse cure the meat. (For a discussion on this, see my article, Saltpeter, Horse Sweat and Biltong)  My point is that this is a good example of a curing technique that was used for a time only and then disappeared, only to be re-appear when conditions required it. Such was the case, I suspect when sal ammoniac was used for a time in curing until the requirement subsided, salt curing became popular again and much later economic factors re-introduced an improved curing salt which by this time was saltpetre. The inclusion of saltpetre into curing salt mixes goes hand in hand with its increased availability.

German and Austrian cookbooks pre-1600’s reveal that vegetable dyes were used to bolster colour in this time and speak of curing with salt only. It is well known that the Germans and Austrians were familiar with nitrate curing and, I will argue, they would have been acquainted with sal ammoniac as a curing salt also, but for whatever reason, these fell out of common practice. When the requirements disappeared for nitrate and sal ammoniac curing of the ancient world, the nations of Europe and China reverted to salt curing.

The many references to salt curing are therefore not surprising in the context of a mature and stable society. A record exists from Cato the Elder who described in 160 BCE how a ham should be cured.  In his Latin work, De Agricultura (On Farming), this Roman statesman and farmer, gives an ancient recipe for curing pork with salt.

“After buying legs of pork, cut off the `feet. One-half peck ground Roman salt per ham. Spread the salt in the base of a vat or jar, then place a ham with the skin facing downwards. Cover completely with salt. After standing in salt for five days, take all hams out with the salt. Put those that were above below, and so rearrange and replace. After a total of 12 days take out the hams, clean off the salt and hang in the fresh air for two days. On the third day take down, rub all over with oil, hang in smoke for two days…take down, rub all over with a mixture of oil and vinegar and hang in the meat store. Neither moths nor worms will attack it.” (economist.com)

Cato may have imitated a process whereby hams are smoked over juniper and beech wood. The process was probably imported by the Roman gourmets from Germania. (economist.com) It is possible that the process of curing itself was brought to Rome by the military stationed in Germany.

Salt curing remains an important technique for high-end hams and certain bacon. Like nitrite curing, it yields a particular cured colour, but one that is a deeper purple than pink.  For the mechanism behind this, refer to a section in my article on the mechanisms of nitrite curing, Bacterial/ Enzymatic Creation of Cured Colour. This is entirely restricted to long term curing which was the norm at a certain time.

Sal Ammoniac

In 2017 I did an article where I speculated that nitrate curing originated from either the Turpan area in western China or from the Atacama desert in Chile and Peru. In this article, I suggest that nitrate curing of meat is thousands of years old. (Salt – 7000 years of meat-curing) I was working on the assumption that nitrate salts are the only salts that will yield nitrite and nitric oxide, required for meat curing. Between the Atacama desert and Turpan in Western China, Turpan is by far the best candidate for the birthplace of meat curing as it is practised around the world. I recently review further evidence from this area in an article, Nitrate Salts Epic Journey and And then the mummies spoke!

In the course of researching the article, I discovered that sal ammoniac was far more vigorously traded than saltpetre in the early Christian era and possibly for thousands of years before that. Fascinatingly enough, I realised that ammonium chloride will, like nitrates, undergo bacterial transformation into nitrites which will then in the meat matrix yield nitric oxide which will cure the meat. I further discovered that it is an excellent meat preservative, even better than nitrates. Turpan is also probably the only place on earth where sal ammoniac and nitrate salts in the form of sodium nitrate occur in massive quantities side by side.

Chinese authors of antiquity are unanimous that sal ammoniac came into China from Turpan, Tibet, and Samarkand and through Samarkand, it was traded into the Mediterranian along the silk road. There are similar records that it was traded from Turpan along the silk road through the city of Samarkand that had strong trading ties with the Mediterranean. It all makes for an appealing case for sal ammoniac as the actual curing salt from antiquity that was used in meat curing when the practice spread around the world. There is even a tantalizing link between Turfan and the ancient city of Salzburg in that a very particular stitch was found in jerseys on mummies in Turfan and in salt mines in Salzburg. This leads me to speculate that the trade of sal ammoniac was done into the heart of Western Europe, into what became known as Austria. This leads me to believe that the actual technological progressions may have come from Austria. Whether it was Salzburg or Turfan is not clear. More work remains to be done to gain greater insight.

We are not familiar with this salt in the context of meat curing and it will be in order for me to dwell on the topic a bit. I reviewed modern references dating back to the 1700s, 1800s, and 1900s where it continued to be used in meat preservation in Nitrate Salts Epic Journey. Several minerals exist composed of ammonium (NH4). Ammonium is formed by the protonation of ammonia (NH3). Sal ammoniac is the most well known and was named by the ancient Romans.  They collected this salt which was found around the temple of Jupiter Ammon in Egypt and called it salt (sal) of Ammon (ammonocius). The name ammonia was subsequently derived from it. It forms in volcanic vents and after volcanic eruptions before it has rained which dissolves it. It is highly soluble. It is unique in that the crystals are formed directly from the gas fumes and bypass the liquid phase, a process known as sublimation.

Ammonium readily combines with an acid thus forming a salt such as hydrochloric acid to form ammonium chloride (sal-ammoniac) and with nitric acid to form ammonium nitrate. Recent studies have shown that volcanos release a “previously unconsidered flux of nitric acid vapour to the atmosphere. (Mather, T. A., et al, 2004) It is a fascinating and insightful fact that the Turfan area, both the basin and the mountains are replete with different salts containing nitrogen (nitrate salts and ammonium) any one of which could be used effective in meat curing.

Sal ammonia was mined from openings in the sides of volcanic mountains where steam from underground lava flows created the ammonium chloride crystals. These were traded across Asia, Europe and India. Massive sodium nitrate deposits occur in the Tarim Basin, the second-lowest point on earth. I then speculate that traders used some of these deposits to forge ammonium chloride since the ammonium chloride crystals did not survive in crystal form on long voyages due to their affinity for water that breaks the crystal structure down. Once this happened, the sodium nitrate and the ammonium chloride look similar in appearance. Due to the fact that it is known that almost all the sal ammonia mined in Samarkand was exported, I deduce that demand outstripped supply and this provided the incentive for such forgery. I find support for the likelihood of such a forgery, not just in the limited supply of sal ammoniac compared to nitrate salts, but also in the fact that mining then sal ammoniac was a seasonal affair and extremely dangerous and a difficult undertaking.

It seems likely that sal ammonia was the forerunner of saltpetre as the curing agent of choice. It is composed of two ions, ammonium, and chloride. The ammonium would be oxidized by ammonia-oxidizing bacteria (AOB) into nitrites and the well-known reaction sequence would result. (Reaction Sequence)

Not only would it result in the reddish-pinkish cured colour, but it was an excellent preservative. In my personal experience, it is a better preservative than salt and nitrites alone but more work is needed to confirm this. There is, however some evidence of this fact from history. An 1833 book on French cooking, The Cook and Housewife’s Manual by Christian Isobel Johnstone states that “crude sal ammonia is an article of which a little goes far in preserving meat, without making it salt.” (Johnstone, C. I.; 1833: 412) It is, of course, the sodium which tastes salty in sodium chloride and ammonium chloride will have an astringent, salty taste. I know exactly what ammonium chloride tastes like since it was added to my favourite Dutch candy “Zoute Drop” with liquorice. I believe it was none other than my old friend, Jan Bernardo who first gave me Zoute Drop. As a boy, I used to ride my bicycle once a month to the only Greek Caffe in Vanderbijlpark which sold it for my monthly fix. My favourite was the double strength version called “Dubbel Zoute Drop.”

Subsequent to these discoveries, I did two small tests with sal ammoniac. Refer to The Sal Ammoniac Project.  Here I show that sal ammoniac stands up to its reputation as an excellent preservative and definitely cures meat in two weeks at a 5 deg C temperature.

Salt with a little bit of saltpetre

Saltpetre is the curing salt that most of us are familiar with that preceded sodium nitrite as curing agent. By far the largest natural known deposits of saltpetre to the Western world of the 1600s were found in India and the East Indian Companies of England and Holland plaid pivotal roles in facilitating its acquisition and transport. The massive nitrate fields of the Atacama desert and those of the Tarim Bason were still largely unknown. In 1300, 1400 and 1500 saltpetre had, however, become the interest of all governments in India and there was a huge development in local saltpetre production.

In Europe, references to natron emerged from the middle of the 1500s and were used by scholars who travelled to the East where they encountered both the substance and the terminology. Natron was originally the word that referred to saltpetre. Later, the word natron was changed and nitron was used.

At first, the saltpetre fields of Bihar were the focus of the Dutch East Indian Company (VOC) and the British East Indian Company (EIC). The VOC dominated the saltpetre trade at this point. In the 1750s, the English East Indian Company (EIC) was militarised. Events soon took place that allowed for the monopolization of the saltpetre trade. In 1757 the British took over Subah of Bengal; a VOC expeditionary force was defeated in 1759 at Bedara; and finally, the British defeated the Mughals at Buxar in 1764 which secured the EIC’s control over Bihar. The British seized Bengal and took possession of 70% of the world’s saltpetre production during the latter part of the 1700s. (Frey, J. W.; 2009: 508 – 509)

The application of nitrate in meat curing in Europe rose as it became more generally available. Later, massive deposits of sodium nitrate were discovered in the Atacama Desert of Chile and Peru and became known as Chilean Saltpeter. Curing with this was, as I have said before, only a re-introduction of technology that existed since well before 2000 BCE.

The pivotal area where I believe saltpetre technology spread from across Asia, India and into Europe, is the Turpan-Hami Basin in the Taklimakan Desert in China. Here, nitrate deposits are so substantial, that an estimated 2.5 billion tons exist, comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. (Qin, Y., et al; 2012)  (The Tarim Mummies of China) Its strategic location on the silk road, the evidence of advanced medical uses of nitrates from very early on and the ethnic link with Europe of people who lived here, all support this hypothesis.

Large saltpetre industries sprang to the South in India and to the South East in western China. In India, a large saltpetre industry developed in the north on the border with Nepal – in the state of Bihar, in particular, around the capital, Patna; in West Bengal and in Uttar Pradesh (Salkind, N. J. (edit), 2006: 519). Here, it was probably the monsoon rains which drench arid ground and as the soil dries during the dry season, capillary action pulls nitrate salts from deep underground to the surface where they are collected and refined. It is speculated that the source of the nitrates may be human and animal urine. Technology to refine saltpetre probably only arrived on Indian soil in the 1300s. Both the technology to process it and a robust trade in sal ammoniac in China, particularly in western China, predates the development of the Indian industry. It is therefore unlikely that India was the birthplace of curing. Saltpetre technology probably came from China, however, India, through the Dutch East Indian Company and later, the English East Indian Company became the major source of saltpetre in the west.

To the South East, in China, the largest production base of saltpetre was discovered dating back to a thousand years ago. Here, a network of caves was discovered in 2003 in the Laojun Mountains in Sichuan Province – possibly the largest production base of saltpetre in China from 1000 years ago. Meat curing interestingly enough is also centred around the west and southern part of China. Probably a similar development to the Indian progression.

In China, in particular, a very strong tradition of meat curing developed after saltpetre was possibly first introduced to the Chinese well before 2000 BCE. Its use in meat curing only became popular in Europe between 1600 and 1750 and it became universally used in these regions towards the end of 1700. Its usage most certainly coincided with its availability and price. I have not compared price and availability in Europe with the findings on its use in meat curing which is based upon an examination of German and Austrian kook books by Lauder (1991), but I am confident that when I get to it one day, the facts will prove the same.

The Dutch and English arrived in India after 1600 with the first shipment of saltpetre from this region to Europe in 1618. Availability in Europe was, generally speaking, restricted to governments who, in this time, increasingly used it in warfare. (Frey, J. W.;  2009) This correlates well with the proposed time when it became generally available to the European population as the 1700s from Lauder. I believe that a strong case is emerging that the link between Western Europe and the desert regions of Western China was the place where nitrate curing developed into an art. The exact place, I believe, in Western China is the Tarim depression.

Dry curing of meat changed from salt only to a mixture of salt and saltpetre, liberally rubbed over the meat.  As it migrates into the meat, water and blood are extracted and drained off.  The meat is usually laid skin down and all exposed meat are plastered with a mixture of salt and saltpetre.  Pork bellies would cure in approximately 14 days. (3) (Hui, Y. H.,  2012: 540)

Salt, Saltpeter, and Sugar

The addition of sugar which favours the reduction of nitrate to the active agent nitrite became common practice during the 19th century.” (Lauer K. 1991.) At first, it was added to reduce the saltiness of the meat and make it generally more palatable. Curers soon discovered that when sugar is added, the meat cures faster and the colour development is better.

Science later revealed that the sugars contribute to “maintaining acid and reducing conditions favourable” for the formation of nitric oxide.” (Kraybill, H. R..  2009)  “Under certain conditions reducing sugars are more effective than nonreducing sugars, but this difference is not due to the reducing sugar itself. The exact mechanism of the action of the sugars is not known. It may be dependent upon their utilisation by microorganisms or the enzymatic systems of the meat tissues.” (Kraybill, H. R..  2009)

Ralph Hoagland, Senior Biochemist, Biochemie Division, Bureau of Animal Industry, United States Department of Agriculture, discovered that saltpetre’s functional value upon the colour of meat is its reduction to nitrites and the nitrites to nitric oxide, with the consequent production of NO-hemoglobin. He showed that the reactant is nitrous acid (CodeCogsEqn (19)) or one of its metabolites such as nitric oxide (CodeCogsEqn (13)).

He wrote an important article in 1921, Substitutes for Sucrose in Cured Meats. Writing at this time, this formidable meat scientist is ideally placed to comment on the use of sugar in meat curing in the 1800s since the basis of its use would have been rooted in history.

He writes about the use of sugar in meat curing in the USA and says that it is used “extensively.” He reveals that according to government records, 15,924,009 pounds of sugar and 1,712,008 pounds of syrup, totalling 17,636,017 was used in curing meats in pickle in establishments that were inspected by the US Government, in 1917. If one would add the estimated use of sugar in dry cures in the same year, he placed the usage at an estimated total of 20,000,000 pounds. This estimate excludes the use of sugar in meat curing on farms. (Hoagland, R.  1921.)

Hoagland says that the functional value of sugar in meat curing at this time (and probably reaching back into the 1800s) was entirely related to product quality and not preservation. “Sugar-cured” hams and bacon were viewed as being of superior quality. He states that a very large portion of bacon and hams produced in the USA are cured with sugar or syrup added to the cure. The quantity of sugar used in the curing mix is so small that it does not contribute to meat preservation at all.  “Meat can be cured in entire safety without the use of sugar, and large quantities are so cured.”  (Hoagland, R.  1921.)

The contribution to quality that he speaks about is probably related to both colour and flavour development. The colour development would have been related to the formation of the cured colour of the meat (The Naming of Prague Salt) as well as the browning during frying.

The role of sugar in bacon curing of the 1800s when saltpetre was used was elucidated in 1882 by Gayon and Dupetit, studying and coining the term “denitrification” by bacteria. The process whereby nitrate is changed to nitrite is through the process of bacterial denitrification. They demonstrated the effect of heat and oxygen on this process and more importantly for our present discussion, “they also showed that individual organic compounds such as sugars, oils, and alcohols could supplant complex organic materials and serve as reductants for nitrate.”  (Payne, 1986)

Denitrifying bacteria are facultative anaerobes, that is, they will only use nitrate (codecogseqn-2) if oxygen (CodeCogsEqn (3).gif) is unavailable as the terminal electron acceptor in respiration.”  “The codecogseqn-2 is sequentially reduced to more reduced forms although not all bacteria form gas. ” “Many bacteria can only carry out the reduction of codecogseqn-2 to CodeCogsEqn (5).gif, and this process is referred to as dissimilatory nitrate reduction. There is also evidence emerging that certain bacteria can denitrify, even if codecogseqn-3  is present.  (Seviour, R. J., et al..  1999:  31)

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(Seviour, R. J., et al..  1999:  31)

“The rate of denitrification is affected by several parameters including temperature, dissolved oxygen levels and the concentration and biodegradability of carbon sources available to these cells” (Seviour, R. J., et al..  1999:  223) Examples of such carbon sources are sugar, oxygen and plant oils.

In the 1800s when the use of saltpetre was at its pinnacle, the use of sugar with saltpetre had then a much more prominent role in that it energizes denitrification bacteria which results in an increased rate of nitrate reduction to nitrite and therefore would speed up curing with saltpetre and result in a better overall curing process. Today, with the widespread use of sodium nitrite in curing brines, certain denitrifying bacteria is one mechanism for NO formation which directly leads to better curing. The use of sugar or dextrose in bacon production in the modern era has more to do with the browning effect through the well-known Millard reaction to give fried bacon a nice dark caramel colour when fried.

Double Salting

In order to dry the meat quicker, a practice developed to salt it multiple times. During the first salting, meat juices are pulled from the meat. This was cleared away and a second “salting” was administered. Later on, several “saltings” were administered. Right here from the southernmost point of the African continent comes a great illustration of this from the early 1700s which then, easily extends back several hundred years.

Remember that the settlement which became Cape Town was in the first place set up as a refreshment station for the Dutch East Indian ships that rounded the African continent en route to India from Amsterdam. It became a stop-over for any friendly ship and Cape Town soon got the name of Tavern of the Sea. Here the summers are extremely hot from December to March or mid-April. Winter starts when the first Arctic cold fronts arrive in April and lasts till at least September. From September to December, it’s technically summer, but it’s often very cold and rainy with intermitted very hot spells. This means that April to August would be the only four months to properly cure meat which was very important for the Cape economy as it would be sold to passing ships. The pressure would have been relentless to find ways to cure meat in the other months also. This is then the background to the account of multiple saltings.

Upham reports on the following course of events from 1709. A detailed treatment of the reference can be seen at Saltpeter, Horse Sweat and Biltong. What was happening in the sweltering heat of March in Cape Town was that meat that was salted for sale to ships were off. A certain Michiel Ley then suggested that the meat should be salted in a two-step process. In other words, salt it and let it lay for a couple of days, giving time for blood and meat juices to be drawn out. Then, give it a second salting. Lay originally came to the Cape as a soldier employed by the Dutch East Indian Company but he changed his occupation to that of a master butcher. Certainly, this was his trade which he received in Europe.

An extract from 28 March 1709 from a Broad Council Meeting at the Cape of Good Hope gives us the rest of the story. It is clear from the entry that they were under pressure to supply due to both supply and increased demand. They noted, “Not one hardly offered himself for the supply of dried or smoked meat. Only 2,500 or 3,000 Ibs. were offered – a quantity very little among so many vessels. The necessity of supplying the ships properly is re-iterated.” The reason for the short supply was the prices offered by the Company which was too low and consequintly the farmers were reluctant to sell.

The small quantity of meat that they received was itself unsuited for sale. They minuted that the “Governor and flag officers inspect some meat salted 8 days ago by the contractor Husing. The lean parts were found good, but the thick parts already spoiling“.

Michiel Ley came up with a plan that was accepted. “Decided that the treat should first lie some days in the brine to draw out the blood, and after that placed in new salt. That was not the idea of Husing but of his fellow contract or Michiel Ley. The former believed that the meat should be left in its first salt and not pickled beforehand; And was prepared to guarantee supply remaining good.” This dispute clearly shows that double salting was by no means an accepted technique in the 1600s and early 1700s.

The decision was made. “Decided, however, to adopt the plan of double salting, recommended by Ley; Husing ordered to supply in that manner; “Meervliet” having brought sufficient casks for the purpose. Ley to supply his share according to his plan. Company to supply the pepper.” The meat which was previously salted by Husing was also given over to Ley. “Decided to take over for the Company, the meat already salted by Husing. The good portions to be distributed among the crews, & the tainted ones among the slaves …

So it happened that Lay was contracted to supply all the meat required by the Company together with Willem Basson, Jan Oberholster, and Anthony Abrahamsz. The issue of the supply of meat was major and shaped the immediate political landscape of the colony. Remember that we said that the prices offered by the Company for meat was too low and the farmers refused to sell. South Africans are well familiar with the fact that Van der Stell was recalled and that Adam Tas was involved in the saga. Adam Tas was one of these farmers and he took it upon himself to collect signatures for a petition against the governor at the Cape. Governor Van der Stel was eventually recalled to Holland. Van der Stel’s reply to the petition against him was a document drafted by him in his defence and signed by among other Ley and Oberholster. The four partners requested that their meat contract be cancelled which was granted and it was taken over by Claas Henderiksz Diepenaar. Adam Tas was locked up in the Castle’s notorious dungeon and finally, Van der Stel was recalled to Holland in 1708. The meat contract was the issue at the heart of Van der Stel’s recall.  (Linder) Ley acted as one of Van der Stel’s representatives to finalize the sale of his assets. (Stamouers)

Notice the black pepper which was added. The reason for this was probably to keep flies and other insects away.

Brine-soaking (brine cure – no pumping)

Brine-soaking followed dry-salt-curing. Note that dry or wet curing is defined by what the meat is left in to cure and not what is applied to the meat. Wet brine curing is still relatively slow and meat pieces are placed in a mixture of salt, saltpetre, and water. It is important to take temperature into account since spoilage may occur before the brine had a chance to penetrate the meat. (Hui, Y. H.,  2012: 540) Here the temperature is very important and is the reason why curing was only done in the winter months.

An 1830 description of a “wet cure” survived where a farmer describes the dry cure method as “tedious.” He credits Europe as the birthplace of the wet-cure method. One of the benefits of this simple system is that it can be used for mutton and beef also. The downside is that it is more expensive than dry-cure, but the wet cure could be re-used and taking everything into account, would work out cheaper in the long run than dry-cure. (The Complete Grazier, 1830:  304) It seems then that wet-curing was invented in the late 1700s or early 1800s.

This re-using of the brine would turn out to become the cornerstone of the industrial revolution for bacon curing and the country credited for this development is Ireland. Before we get to that, we have to first look at barrel pork.

Barrel pork

Barrel pork was an easy way to cure pork that involved liquid brine. It had the benefit that it could be put in barrels, loaded onto a wagon or a ship for transport and cure in transit. It could also be stored in the cure which would render it safe from flies and other insects. References to it show that it was practised already by the second half of the 1700s and well into the 1800s.

In the 1800s, this was the main way that the packing plants in the USA exported pork to England as bacon. There are many accounts in newspapers of the time where advice is given to the bacon producers on how to make sure that the meat arrives in England unspoiled. One of the main points was the importance of using good, new wood for the barrels.

A 1776 description is given on how barrel pork was produced. “After the meat has cooled < probably after the hair was removed >, it is cut into 5 lb. pieces which are then rubbed well with fine salt. The pieces are then placed between boards a weight brought to bear upon the upper board so as to squeeze out the blood. Afterwards, the pieces are shaken to remove the surplus salt, [and] packed rather tightly in a barrel, which when full is closed. A hole is then drilled into the upper end and brine allowed to fill the barrel at the top, the brine being made of 4 lb. of salt (1.8kg or 10%), 2 lb. of brown sugar (0.9kg or 5%), and 4 gallons of water (15L or 84%) with a touch of saltpetre. When no more brine can enter, the hole is closed. The method of preserving meat not only assures that it keeps longer but also gives it a rather good taste.” (Holland, LZ, 2003: 9, 10)

Again, notice the brine make-up of salt, saltpetre, sugar mixed with water. The role of the sugar was to break the hard salt taste.

Barrel pork would remain an important curing method throughout the 1700s and would make a spectacular return almost 100 years later when pressure pumps were introduced to inject the brine into the meat through needles.  A plank would be run across the barrel opening. The meat is placed on the plank for injection with between one and three needles. The three needles are fed brine through a hand pump that would pump brine directly from the barrel.  The barrel is half-filled with brine. After the meat has been injected, it is pushed off the plank, to fall into the brine which acts as a cover brine.  It would remain in the cover brine the prescribed time before it is removed and smoked.

The invention of Mild Cured Bacon by William Oake

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Ham press from the 1910s

Sometime before 1837 William Oake, a chemist from Ireland invented Mild Cured Bacon. (Chapter 09.01 – Mild Cured Bacon) This was the first major development in curing technology following barrel curing. The essence of mild curing is the continued re-use of the old brine. Oake was investigating what was responsible for the preservation power in the salt/saltpetre mix. He correctly concluded that salt plays a very limited role in preservation and today we know that its main function in old dry curing systems was to reduce the moisture in the meat and thus lowering the water activity. He also found no great preserving power in saltpetre but he knew that “nature” provided somehow a preserving power to the meat. It was known that the re-use of old brine had a large benefit and we know that this probably came to England from the German region of Westphalia. So, at this time, there was a practice in England to re-use brine twice. One would cure the meat with the liquid brine, boil it in an attempt to “clean it”, and re-use it a second time. (For a full discussion on this, see William and William Horwood Oake)

There is no doubt that Oake used all these different influences and inspirations to develop the system of continually re-use the brine. This is the key feature of his brilliance. Yes, a second and vital contribution is to look at the full process and reorganise it in a way that makes sense in a factory environment. He industrialised bacon production. This made great bacon affordable and available to the general public. His system incorporated the following elements.

  • Lightly salting the meat to draw out the blood on the concrete factory floor
  • Tanking or brining (stacking and pickling) for 7 days which involved sprinkling the bottom of the tank where the meat would be cured with salt. Stack the flitches on the bottom. Lightly sprinkle saltpetre over it with sugar and salt. The next layer of flitches is stacked on top of the first but done crosswise. This is again sprinkled exactly as was done with the first and so it is repeated till the tank is full. A lid is now placed inside the tank with an upright on top and pickle is poured into the tank. The lid and upright serve the purpose of keeping the bacon sides submerged. The pickle is made as follows: To every 10lbs. of salt we add 8lbs. of dark-brown sugar; 1 lib. of spice, and 1/2lb. of sal-prunella.” Sal prunella a mixture of refined nitre and soda.  Nitre is refined saltpetre used in the manufacturing of explosives. Saltpetre plays a very important role as does the grade of saltpetre used. It is important to turn the meat over after forty-eight hours into another tank.  The meat that was on top is placed at the bottom of the next tank. Salt, sugar, and saltpetre are again used exactly as it was done during the first salting. Now the real trick comes in. The same pickle is used!”
  • Maturing/ Resting and Drying for 21 days. After seven days the flitches are removed and stacked on the floor putting some salt between each layer. Be careful not to stack it higher than four sides deep, until it has been on the floor for some days when it should be turned over, and stacked higher each time until the fourth week from the day it went into the tanks; the bacon will then be cured.”
  • Washing, drying, trimming and smoking. Place the bacon in tanks of cold water. Here it is soaked overnight. The next morning we wash them well with a brush. Whether smoking is done or not after tank curing the meat should be rinsed off and dried before aging or maturation. The reason for this is that the meat pores should be closed leading to a hardening of the surface and a considerable reduction in the drying rate. The meat is trimmed and hung till it is properly dried. It is then smoked. 

Two aspects should be noted. One is the rigid stepwise process which addressed efficiency, speed and hygiene and the second is the re-use of the old brine. Oakes genius was combining existing curing steps in a new way and the quality of his brine. His lasting contribution is, however, without any doubt, the creation of the live brine system which became the cornerstone of tank curing.

The system was next adopted by the Danes. The year was 1880. Denmark is a tiny nation. To remain competitive, they realised years earlier to learn as much as they can from other nations and peoples and adapt. Every industry in Denmark was constantly looking where new discoveries were being made and how they can adopt and adapt it.

Denmark had large dairy farmers and a sizable pork industry developed from the by-products of dairy farming. It was very simple and profitable. Raise pigs on the byproducts from milk and sell it to England and Germany. Someone from the pork industry learned about the new mild cured bacon produced in Ireland. They tried many times to sent people to learn the techniques, but the Irish were careful not to employ the young Danish men who were sent over for employment in the large bacon plants in Ireland. They needed an opening in the Irish market to learn their techniques. Such an opening was presented through industrial action by the Irish workers. The thing about Ireland is that the workers often go on strike and how they are treated by the companies they work for is often very harsh. Those on strike do not get paid and stand a large chance to be laid off.

In 1880 there was a strike among butchers in the Irish town of Waterford. Some shrewd members of the Danish pork processing guild happened to be in Ireland at that time, in Waterford and at the promise of lucrative employment in Denmark managed to persuade a number of the striking men to return with them to Denmark. In Denmark, they quickly arranged for them to train the Danish butchers. Mild Cured Bacon became the new Danish bacon.

Sweet Cured Bacon by C & T Harris (Dry-salt-curing in combination with injection)

In Calne, a small settlement in Wiltshire, England, the firm C & T Harris was becoming the world leader in producing exceptional mass-produced bacon. For a complete discussion, please read Chapter 10.02 – Sweet Cured Harris Bacon.

Their invention was very similar to the general method of William Oake’s Mild Cured Bacon with the notable exception of the re-use of the old brine. Very importantly, they hot smoked their bacon after curing. Even more importantly was the fact that this invention in the 1840s used stitch pumping. Stitch pumping itself was invented around this time and it allowed for much quicker curing of the meat which together with hot smoking cut the curing time down and was a major improvement on the taste. It was not a had salted taste, but a mild cure taste and from there the name.

It seems that the basic distinguishing between dry and wet curing is not based on whether injection is applied or not, but the state of the salts that the meat is left in, even after it has been injected with a brine (mixture of salt and water). So, if it is packed in a dry mix, it is dry curing and if it is soaked in a brine, it is wet curing.

It was reported by some bacon curers that they used the dry-curing in conjunction with injection. In this case, the meat is injected with approximately 10% saturated brine solution and the injected meat is then treated the usual way in the application of dry-salt-cure. There is a record showing that C & T Harris (Calne) used injection with their bacon from 1843. After it was dry-cured, the meat was smoked at a temperature of not higher than 38 deg C (100 deg F) in order to prevent nitrate burn which presents itself as green spots that appear on the meat. In the report, mention is also made that care should be taken if these products are stored to prevent damage from insects such as cheese skippers, mites, red-legged ham beetles, and larder beetles.  (Hui, Y. H.,  2012: 540) The result was sweet cured bacon!

The Injection of Meat

A short review of the invention of the practice of brine injection with needles is appropriate at this time. The practise started as a way to preserve cadavers. I remember an account I read of how Von Hombult and Guthrie went from house to house after a particularly heavy thunderstorm buying up the copses of the deceased for their own medical studies. Before the age of refrigeration, preserving human remains to study the make-up of the human body would have received considerable attention and this was the first area where injection of meat was done for the purpose of preservation.

The link between meat preservation for sustenance and meat preservation for the study of anatomy is, as the link between meat injection and the medical establishment, one that is abundantly obvious if you just think about it for a minute, but not necessarily the first connection you make when you look at the different disciplines separately. The man who took front and centre stage in the development and progressed the practice of injecting preserving fluids into dead animal muscles for the purpose of preservation was Morgan.

Morgan’s Patent

It was a certain Mr Morgan, in England, who had a significant impact on popularising the technique of injecting a liquid brine into the meat in the first place. The motivation was to increase the rate of curing by getting the brine faster into the meat in order to reduce the time required for processing which became the basis of sweet cured bacon.

In temperatures above 20 deg C, pork spoils in three days. By injecting a liquid brine into the meat at evenly spaced intervals, the brine diffuse quicker through the meat. Morgan’s interest was the preserving of meat generally but included meat preservation for long sea voyages before the advent of refrigeration and not the curing of meat by farmers.

We encountered Mr Morgan in the work of Edward Smith, Foods, (1873). Smith wrote that “Mr Morgan devised an ingenious process by which the preserving material, composed of water, saltpetre, and salt, with or without flavouring matter, was distributed throughout the animal, and the tissue permeated and charged. His method was exemplified by him at a meeting of the Society of Arts, on April 13, 1854, when I [Edward Smit was] presided.” (Smith, 1873)

He describes how an animal is killed in the usual way, the chest opened and a metal pipe connected to the arterial system. Brine was pumped through gravity feed throughout the animal. Approximately 6 gallons were flushed through the system. Pressure was created to ensure that it was flushed into the small capillaries. Smith reported overall good results from the process with a few exceptions. He himself seemed unconvinced.

An article appeared in the Sydney Morning Herald that mentions Dr Morgan and his arterial injection method. An important observation from the article is the date of 1870. By this time, he is referred to as “Dr Morgan”, cluing us in about the timeline of Morgan’s life.

A second observation is a drawback of the system. The article states that “salting is the most common and best-known process of preservation (of meat), the principal modern novelty being Dr Morgan’s plan of injecting the saline solution into the arterial system – the principal objection to which has been that the meat so treated has been over-salted.” (Sydney Morning Herald, 1 March 1870, p 4) The brine mix that Mr Morgan suggested was 1 gallon of brine, ¼ to ½ lb. of sugar, ½ oz. of monophosphoric acid, a little spice and sauce to each cwt of meat. (Smith, E, 1873: 36)

Seventeen years after Smith met Morgan at the Society of Arts meeting, in 1871, Yeats reported that a certain “Professor Morgan in Dublin, proposed a method of preservation by injecting into the animal as soon as it is killed, a fluid preparation, consisting, to every hundredweight of meat, of one gallon of brine, half a pound of saltpeter, two pounds of sugar, half an ounce of monophosphoric acid, and a small quantity of spice.” (Yeats, J, 1871: 225)

The plan was widely tested at several factories in South America and by the Admiralty, who had reported that they had good results from the technique. (Yeats, J, 1871: 225, 226) It was in all likelihood the same Morgan that Smith reports on who, by 1871, became a professor in Dublin. Notice, as a matter of interest that he used the same basic brine mix of salt, water, saltpetre, sugar, monophosphoric acid and spices. This, together with the similarity in surname makes it quite certain that Mr Morgan, Dr Morgan and Prof. Morgan is the same person. In itself, this is an example of perseverance! In 1854 his arterial injection was met with scepticism where Yeats reports in 1871 that the Admiralty viewed his improved method.

Was this Morgan’s Invention?

The concept of arterial injection was not new. By the time Morgan demonstrated it to the Society of Arts, on April 13, 1854, it may have been as old as 150 years, used for embalming corpses for the purpose of medical studies. This invention is credited by some to the Dutch physician, Frederik Ruysch (1638 – 1730). He injected a preservative chemical solution, liquor balsamicum, into the blood vessels, but his technique remained largely unknown for some time. (Bremmer, E.; 2014)

British scientists who used arterial injection and from whom Morgan could have learned the system were the Hunter brothers William (1718–1783) and John (1728–1793) and their nephew, Matthew Baillie (1761–1823). The injection was into the femoral arteries. They all injected different oils, mainly oil of turpentine, to which they added Venice turpentine, oil of chamomile, and oil of lavender. Vermillion was used as a dye to create a more life-like skin colour, but would also have added preservation to the final solution. (Bremmer, E.; 2014)

There is a reference from 1837, on an essay delivered on the operation of poisonous agents upon the living body by Mr John Morgan (1797 – 1847), F.L.S Surgeon to Guy’s Hospital. (1837; Works on Medicine) The same publication contains an article by Dr Baillie, M.D. on the morbid anatomy of some of the most important parts of the human body. John Morgan was undoubtedly well familiar with arterial injection. Not only due to the fact that he was a contemporary of Baillie, but he was also a demonstrator of anatomy at the private school near Guy’s Hospital. (livesonline.rcseng.ac.uk/) The late 1830 article that is referenced means that it fits the timeline perfectly for a late 1830 or early 1840 technology transfer for the use of the same general technique of injecting preserving fluids into the meat of a pigs carcass which presumably became stitch pumping, a precursor for Morgans invention.

John Morgan is in all likelihood the father of Dr John Morgan (Circa 1863), who was professor of anatomy at the University of Dublin. A process of arterial injection is described that was used by Dr John Morgan from the University of Dublin. ” John Morgan, a professor of anatomy at the University of Dublin in Ireland, formally established two principles for producing the best embalming results: injection of the solution into the largest artery possible and use of pressure to push the solution through the blood vessels. He also was among the first to make use of a preinjection solution as well as a controlled drainage technique. Morgan’s method required that the body be opened so the heart was visible, then an 8-inch pipe was inserted into the left ventricle or aorta. The pipe was connected to yards of tubing ending in a fluid container hung above the corpse. The force of gravity acting on the liquid above the body would exert about 5 pounds of pressure, adequate to the purpose of permeating the body.” (Wohl, V.) This process described here is applied, not to the preservation of animal carcass, but for embalming a human body! It is, however, the exact same process that he demonstrated years earlier in London to Smith at the Society of the Arts meeting on 13 April related to carcass preservation.

From the process description, it is clear that we have identified Morgan, father of the arterial injection method in meat curing as Dr John Morgan, professor of anatomy at the University of Dublin, son of John Morgan, Surgeon to Guy’s Hospital. The original inventor of the system was the Dutch physician, Frederik Ruysch and the application was embalming.

Henry Denny and the claim of a Return to Dry Salting

No review of curing history will be complete without mentioning the legendary Henry Denny and the equally legendary company founded by him.

From the official website of Henry Denny & Sons.

Ireland in the first half of the 1800s was a fertile field for innovation. An excellent example is found in the person of Henry Denny. Part of his remarkable legacy is a firm that once was the largest bacon producer in Europe, Henry Denny & Sons. Henry was born in Waterford, Ireland in 1790.

Denny started out as a provisioner merchant in Waterford. The first reference to him as a bacon merchant comes to us from 1846. In 1854 he started using ice in bacon curing which allowed him to cure meat all year round like his colleagues in Calne. The bacon he cured was also referred to as mild cured bacon and a patent was granted in 1857 on his process. Like the process invented by C & T Harris, which they called Sweet Cured Bacon, Henry’s process used much less salt. The priority for inventing the first mild cured system, however, goes to William Oake from Ulster whom we know invented this at around the time when Denny had his merchant business or shortly after this and well before Denny entered the pork processing trade.

Henry’s curing system is described in Geocaching where the post seems to be a copy from another work that is unfortunately not referenced and all my attempts to locate the original publication has been in vain. The author describes it as follows: “Until the early 19th century, pork was cured by soaking large chunks of the meat in barrels of brine for weeks. Shelf life was poor, as often as the inside of the chunks did not cure properly, and meat rotted from the inside out. Henry Denny and his youngest son Edward Denny introduced a number of new innovations – he used long flat pieces of meat instead of chunks; and they dispensed with brine in favour of a dry or ‘hard’ cure, sandwiching the meat in layers of dry salt. This produced well cured bacon with a good shelf life and revolutionised Ireland’s meat industry. Irish bacon and hams were soon exported to Britain, Paris, the Americas and India“.

Reference is made to the fact that Denny invented several curing techniques and if the description given is correct, it would be one of several inventions. Taken at face value I doubt the superiority of his system over Oakes invention. It also comes so late in terms of dates that I seriously doubt if this could be the patent that was awarded in 1957. By this time meat injection was already well established which solved the shortcomings of William Oakes invention in his mild cured system of simply filling the curing tanks with brine to diffuse into the meat “naturally.” If this was in fact the patent that was granted in 1857, it would represent a serious step backwards.

The greatest contribution to this review article of Denny is the fact that he acquired a meat curing company in Denmark in 1894. The reference is Lets-Look-Again who also seems to quote an uncredited source. They make a statement that this purchase “introduced Irish meat curing techniques to Denmark.” I have over the years come across several authors who made the same claim that the Irish meat curing system was introduced to Denmark in the late 1800s after an Irish firm acquired a Danish processing company. They never gave the name of the Irish firm in question. The end of the 1800s is, however, the wrong time for the introduction of the Irish system to Denmark. By this time it was already well established in Denmark and the likely transfer of the technology to C & T Harris took place from Denmark either at this time (closing years of the 1800s) or in the opening few years of the 1900s. For this reason, I never used the reference but I was always curious who the Irish firm was, wrongly credited for the transfer of the technology to Denmark. Now I know and for this reason, as well as the widespread nature of the erroneous claim, I include it here.

What seems more probable is the claim that Denny was the inventor of the pork rasher. Geocaching quotes an unnamed source that “the rasher (a piece of bacon to be cooked quickly or rashed) was reportedly invented in 1820 by Henry Denny, a Waterford butcher who patented several bacon curing techniques still used to this day.” It must be mentioned that Dennys career only started in 1820 but that was not as a butcher. It was as a merchant and he entered the pork processing business only in 1854. There could still be credability to the claim which I base on the widspread nature of the story in Ireland. Maybe he was a young man with unusual interest and creativity in selling pork at his trading business. The claim may however be apocryphal.

Pale Dried Bacon and Wiltshire Cure or Tank Cured Bacon

The next major development in curing also came from C & T Harris (Calne). Pale Dried Bacon was invented by them just before they adopted tank curing. It was invented under John Harris in Calne in the 1890s. It is basically the same as Sweet Cured Bacon but instead of hot smoking the bacon, it was dried in special drying rooms and not smoked. The bacon was therefore pale on the outside of the flitches but it was properly dried. From there the name Pale Dried Bacon.

It was just after this, at the closing years of the 1800s or the very first few years of the 1900s that tank curing technology was transferred from Denmark to Calne in Wiltshire. The technology of mild cured bacon of Oake, invented in Ireland, adopted by the Danes finally spread to Calne, Wiltshire and became the famous British Wiltshire bacon curing or Tank curing in the closing years of the 1800s or early 1900s. For a detailed discussion, please refer to Chapter 10.06: Harris Bacon – From Pale Dried to Tank Curing!

Boiling of the brine

founders

The original founders of the St. Edmunds Bacon Factory are shown in this old print of the laying of the factory’s foundation stone in 1911.

We can now return to the 1830 account of wet-curing where we identify important developments in brining technique. The farmer who wrote down the brining technique suggests that the brine mix must be boiled over a gentle fire for the impurities to rise to the top before these were skimmed off and the brine allowed to cool down. (The Complete Grazier, 1830: 304)

When it is cooled down, the brine is poured over the meat so that the meat is completely submerged. Meat from small pigs is kept in the brine for three to four days and longer. An older pig may require one, two, or three days longer. (The Complete Grazier, 1830:  304)

If the meat is intended for hams, it must be left in the brine for two days. At the end of the curing time, rub with pollard (a by-product from the milling of wheat, like bran) and cover with a paper bag to keep flies away. In warm weather, make sure that the blood is all drained from the meat and the meat is rubbed with fine salt before the brine is poured over. (The Complete Grazier, 1830:  304)

Let us look carefully at the description given in the 1830 edition of The Complete Grazier of re-using old brine. The report says that wet cure is more expensive then dry cure unless the brine is re-used. First the meat is well rubbed with fine salt. A liquor is then poured over the meat and “though the preparation of such brine may, at first sight appear more expensive than that prepared in the common way, yet we think it deserves a preference, as it may be used a second time with advantage if it be boiled, and a proportionate addition be made of water, and the other ingredients above mentioned.” (The Complete Grazier, 1830: 304)

The “other ingredients above mentioned” refers to the following. “First, let two ounces of saltpetre, one pound and a half of refined sugar, and four pounds of common salt be boiled in two gallons of pure spring water, over a gentle fire, and the impurities, that may rise to the surface, be carefully skimmed off. When this brine is cold, it should be poured over the meat, so as to cover every part.” (The Complete Grazier, 1830: 304)

Three observations should be made here. The 1830 description indicates that this process is still in its infancy. Liquid brine, it says, may appear to be more expensive than if it is done “in the common way” which in the context should refer to dry curing or rubbing a mixture of dry ingredients onto the meat. Secondly, the edition of the Complete Grazier quoted is from the 5th edition which means that by this time, the description may already be 5 years old if it appeared in the 1st edition. The 3rd observation is that the brine can be used “a second time.”

This means that even though the practice of re using old brine was already described in 1830, possibly as early as 1825, it is still a far cry from the complete system of William Oake and the multiple (continues) re-use of old brines which is one of the cornerstones of the mother brine or live brine system of tank curing. It definitely describes the start of the invention. We also do not know if a continual re-use of the brine was the brain child of William Oake or if this development already took place before Oake incorporated it into his complete system. This would be typical of Oakes invention which took previously proven “best practices” of the time and incorporating it into a new complete system.

It is this old brine or re-used brine that became the cornerstone of the industrial bacon curing plants in Denmark and which they call the “mother brine.” Needle injection of meat along with the faster curing action of the mother brine would become the key feature of curing plants in Denmark and would later be adopted by factories around the world. It was the fastest way of producing bacon and was remarkably effective. The invention of what became known as tank curing or mild cure was, however, not Danish, but Irish!

It shows clearly that by the 1830s which coincides with Oakes invention of mild curing, the practice of re-using the brine was being phased into curing techniques in England. William Youatt who compiled the Complete Grazier repeats this process in his 1852 work, Pigs: A Treatise on the Breeds, Management, Feeding and Medical Treatment of Swine; with directions for salting pork, and curing bacon and Hams. Here he writes, “in three weeks, jowls, &c, may be hung up. Taking out, of pickle, and preparation for hanging up to smoke, is thus performed: — Scrape off the undissolved salt (and if you had put on as much as directed, there will be a considerable quantity on all the pieces not immersed in the brine; this salt and the brine is all saved; the brine boiled down [for re use].” Notice that his 1852 description is far more “matter of fact” and he does not go into all the explanations and caveats he did in the 1830 description.

Youatt gives an important clue about the possible origin of the re-use of brine and it is not surprising that he points to Germany. The region of interest is Westphalia. In the above-mentioned publication, he writes, “The annexed system is the one usually pursued in Westphalia : — ” Six pounds of rock salt, two pounds of powdered loaf sugar, three ounces of saltpetre, and three gallons of spring or pure water, are boiled together. This should be skimmed when boiling, and when quite cold poured over the meat, every part of which must be covered with this brine. Small pork will be sufficiently cured in four or five days; hams, intended for drying, will be cured in four or five weeks, unless they are very large. This pickle may be used again and again, if it is fresh boiled up each time with a small addition to the ingredients. Before, however, putting the meat into the brine, it must be washed in water, the blood pressed out, and the whole wiped clean.”

Another interesting fact emerges from Youatt. In England, at this time, they had no idea of why the re-use of old brine worked so well is clear from the following comment he makes in the publication just mentioned. He writes under the heading, “Poisonous Properties of Brine” the following. “It is a fact worthy of notice that the brine in which pork or bacon has been pickled is poisonous to pigs. Several cases are on record in which these animals have died in consequence of a small quantity of brine having been mingled with the wash, under the mistaken impression that it would answer the same purpose and be equally as beneficial as in the admixture of a small quantity of salt.”

It means that Oake in his Mild Cured system relied on existing technology, albeit it is new and cutting edge in the 1830s. He may or may not have been personally responsible for progressing the ideas such as re-using the old brine a second time to re-using it continually. It seems clear that his single biggest contribution is that he put known components together in one complete system.

Wet-curing in combination with injection (brine cure – with pumping)

stitch injection elmswell-bacon-factory

The first cooperative bacon curing company was started in Denmark in 1887. It was seven years after the visit to Waterford in Ireland in 1880 “taking advantage of a strike among the pork butchers of that city, used the opportunity to bring those experts to their own country to teach and give practical and technical lessons in the curing of bacon, and from that date begins the commencement of the downfall of the Irish bacon industry. . . ” (Tank Curing was invented in Ireland)

It means that the Danes had the technology and when the impetus was there, they used the technology. The impetus, as we already said, was the outbreak of swine flu which saw a ban on Danish pork. They had no choice but to change their export from live pigs to bacon. The detailed description of Oakes invention and his process came to me through an Australian publication from 1889. It means that Ireland not only exported the mild cure or tank curing technology to Denmark but also to Australia, probably through Irish immigrants during the 1850s and 1860s gold rush, between 20 and 30 years before it came to Denmark. Many of these immigrants came from Limerick in Ireland where William Oake had a very successful bacon curing business. Many came from Waterford. A report is given in The Journal of Agriculture and Industry of South Australia, edited by Molineux, General Secretary of Agriculture, South Australia, Volume 1 covering August 1897 – July 1898 and printed in Adelaide by C. E. Bristow, Government Printer in 1898. Apart from giving the complete system as invented by Oake and crediting him for the invention, it also sites one company who used the same brine for 16 years by 1897/ 1898 which takes tank curing in Australia to well before 1880 which correlates with the theory that immigrants brought the technology to Australia in the 1850s or 1860s.

One further note about the invention of tank curing by Oake from Ireland. He was a chemist and his invention had as much to do with the brine makeup as it had to do with the fact that tanks were used. Morgan’s work, already cited in great detail here, shows clearly that curing brine was a priority in Ireland in the mid-1800s. The possibility that Oake and Morgan interacted and possibly influenced each other is a tantalizing likelihood that emerges from the data.

It was Denmark, however, who continued to expand on the tank curing system or mild cured system, as it was called, using a combination of stitch pumping and curing the meat in curing tanks with a cover brine.  (Wilson, W, 2005:  219) Brine consisting of nitrate, salt and sugar were injected into the meat with a single needle attached to a hand pump (stitch pumping). Stitch pumping was either developed by Morgan, whom we looked at earlier or became the forerunner of arterial injection which is solely credited to Morgan.

The meat was then placed in a mother brine mix consisting of old, used brine and new brine. The old brine contained the nitrate which was reduced through bacterial action into nitrite. It was the nitrite that was responsible for the quick curing of the meat. 

The Auto Cure System and the legendary Oak Wood & Co. Ltd. Bacon Curer

The auto cure system is an excellent example of the fact that the power of the used brine was known and who else to have invented it than the son of the man who pioneered the live brine system, namely Willaim Oake! 

William Horwood Oake set his curing operation up in Gillingham, Dorset with partners. It eventually became the famous Oak’ Woods & Co Ltd. Oake invented the system in which was eventually in use in England, Sweden, Denmark, and Canada. William Harwood Oake passed away on 28 September 1889 in his late 40s and Evan R Down took over the running of the company. There is a report that they exported their technology to New Zealand and South Africa also. They patented it around the world and licenced its use to companies in different countries. Down became the driving force for the international expansion on the back of solid patents. The Danes paid a £4,000 annual royalty for the use of the system which was probably applied in many factories across Denmark. They became the premium representation of Wiltshire bacon meaning the curing of whole bacon sides.

The process is as follows. The pig is slaughtered in the usual way and the sides trimmed and chilled. After chilling, it is laid out in rows on a sort of truck that exactly fits into a large cylinder of steel 32 feet long, 6 feet in diameter and which will hold altogether 210 sides. When the cylinder is filled, the lid, weighing 3 ½ tons (7000lb. Danish) is closed and hermetically sealed by means of hydraulic pumps at a pressure of 3 tons to the square inch.

A vacuum pump now pumps all the air out which creates a vacuum of 28 inches. It takes about an hour to pump all the air out. The brine channel which leads to the brine reservoir, holding around 6000 gallons of brine is now opened. The brine rush into the chamber and as soon as the bit of air that also entered has been extracted again, the curing starts.  It happens as follows.

The brine enters the cylinder at a pressure of 120 lbs. per square inch. It now takes between 4 and 5 hours for the brine to enter the meat completely through the pores which have been opened under an immense vacuum. When it’s done, the brine runs back into the reservoir. It is filtered and strengthened and used again.

An advantage of the system is given that the bacon can then be shipped overseas immediately. The time for the total process is around three days. On day 1 the pig can be killed, salted on day 2 and packed and shipped on day 3.

There are two brine reservoirs. The one is used with a stitch pump to inject brine into the sides as usual before they are placed in the cylinder and the second tank is used. The largest benefit of this system is the speed of curing and many people report that the keeping quality of the bacon and the taste is not the same as bacon cured in the traditional way.

For a full discussion on the father-son due of William and William Horwood Oake and their inventions, see William and William Horwood Oake.

autoclave-2

Tank Curing

Denmark was, as it is to this day, one of the largest exporters of pork and bacon to England. The wholesale involvement of the Danes in the English market made it inevitable that a bacon curer from Denmark must have found his way to Calne in Wiltshire and the Harris bacon factories. The tank-cured method, as it became known, was adopted by C & T Harris (Calne). The fact was that it was already in Wiltshire in the company Oake’ Woods & Co. Ltd.. Why it took C & T Harris till the second half of the 1800s to incorporate it into their processes is a good question to which I don’t have the answer yet.

A major advantage of tank curing, as it became known in England, is the speed with which curing is done compared with the dry salt process previously practised. Wet tank-curing is more suited for the industrialisation of bacon curing with the added cost advantage of re-using some of the brine. It allows for the use of even less salt compared to older curing methods. One of the biggest advantages was, however, the increased curing speed as nitrites were used which was already converted from nitrates through bacterial fermentation.

wiltshire injection

The question comes up if we have corroborating evidence that Denmark imported the Irish technology in 1880? Clues to the date of the Danish adaption come to us from newspaper reports about the only independent farmer-owned Pig Factory in Britain of that time, the St. Edmunds Bacon Factory Ltd. in Elmswell. The factory was set up in 1911. According to an article from the East Anglia Life, April 1964, they learned and practised what at first was known as the Danish method of curing bacon and later became known as tank-curing.

A person was sent from the UK to Denmark in 1910 to learn the new Danish Method. (elmswell-history.org.uk) The Danish method involved the Danish cooperative method of pork production founded by Peter Bojsen on 14 July 1887 in Horsens. (Horsensleksikon.dk. Horsens Andelssvineslagteri)

The East Anglia Life report from April 1964, talked about a “new Danish” method. The “new” aspect in 1910 and 1911 was undoubtedly the tank curing method. Another account from England puts the Danish invention of tank curing early in the 1900s. 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, late in the 1800s or early in the 1900’s the Danes imported the Irish system and practised tank-curing which was brought to England around 1911. The 1880 date fits this picture well.

It only stands to reason that the power of “old brine” must have been known from early after wet curing and needle injection of brine into meat was invented around the 1850s by Morgan. Before the bacterial mechanism behind the reduction was understood, butchers must have noted that the meat juices coming out of the meat during dry curing had special “curing power.” It was, however, the Irish who took this practical knowledge, undoubtedly combined it with the scientific knowledge of the time and created the commercial process of tank-curing which later became known as Wiltshire cure.

Why the system was brought over from Denmark when William Harwood Oake’s dad invented the system in Ireland remains a very good question. It is almost impossible to speculate on what exactly was happening in the Harris, Oake ‘ Wood & Co Ltd and in the St. Edmunds Bacon Factory Ltd., but I have a suspicion that Oake Wood was completely focused on their auto cure system in the 1890s and early 1900s and other companies were looking for a less expensive and equally efficient system which the Danish tank curing offered them. I can on the one hand understand why competitors were reluctant to buy into the Oake Wood system of auto curing and on the other hand, why Oake ‘ Woods was reluctant to sell it to strong opposition.

What we know for certain is that tank curing undoubtedly developed from the Oake Woods factory in Gillingham, Dorset and “diffused” into Wiltshire. It was probably independently incorporated into the Harris operation as was the case with the St. Edmunds Bacon Factory Ltd who both claim to have received the technology from Denmark.

Multi-Needle Injection and Vacuum Tumbling and The Direct Addison of Nitrites to Curing Brine

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Multi-needle injector, C & T Harris (Calne) Ltd. C 1960

The composition of the brine changed around 1915 by the direct addition of sodium nitrite. For a thorough discussion on this revolutionary development, see,

Where tank curing used the fermented brine which after fermentation contained nitrites, despite the fact that only nitrates were added to the brine to begin with, along with salt and sugar, nitrites became widely available through pharmacies at this time as it was used in treating certain heart related ailments. Nitrites were now being included directly into curing brines, bypassing the fermentation step.

Multi-needle injectors and vacuum tumblers became commonplace in any met curing operation. It is generally accepted that these developments took place in the mid to late 1900s, but an interesting US patent (number 23,141) was awarded to L. M. Schlarb from Allegheny, Pennsylvania on 3 June 1901 directly related to injection and vacuum machines for meat curing.  (Journal of the Society of Chemical Industry; 1902: 269)

The process is described as “injecting brine and carbon dioxide under pressure into the meat by means of suitable needles connected to a tank containing the brine and carbon dioxide, the pressure in the tank being about 2 atmospheres.” The nozzles it talks about maybe the three-needle injectors that were used until the middle of the 1900s and the unique aspect of the patent was the use of brine in conjunction with carbon dioxide. (Journal of the Society of Chemical Industry; 1902: 269)

The next bit is fascinating as it is possibly the earliest recorded date of the use of a vacuum machine in meat processing. The patent is described in a journal article that “the meat is now placed in a vessel from which the air is exhausted, and brine is then allowed to flow in. The meat is allowed to remain in the brine for about 10 hours, and may then be subjected to the action of carbon dioxide under pressure.” If one removes the presence of carbon dioxide, it is then reasonable to assume that a vacuum machine has been in use in one shape or another to facilitate the diffusion of brine into meat, as early as 1901. (Journal of the Society of Chemical Industry; 1902: 269) The process was, however, not new as auto curing was already in use in the second half of the 1800s in many countries across Europe.

Over the next 60 years, the multi-needle injector became bigger, with more needles until the present machines were being produced from the mid-1900s. Tumbling machines, as we know it today has been in use since the early 1970s.

Current Developments

Two major developments are currently taking root across the globe. One is a return to fermented brines where a natural carrier of nitrates are used as the start of brine preparations. A starter culture is then added to this “carrier” which will be something like celery powder or beetroot, high in nitrates and specially grown with high nitrate content in the soil. Salt and phosphates, where permitted, are added along with reducing and non-reducing sugar to complete the modern curing brines.

The second important development in commercial curing plants of the last decade is undoubtedly the introduction of what we call the grid system. According to this method, grids or bacon moulds are used to give the bacon a regular shape. The meat is normally wrapped in banking paper or some film before it is placed in the moulds and in one form or the other, an enzyme, Transglutaminase, is added to the product. The main purpose of this is to achieve higher slicing yields, but in reality, it also accounts for lower smoking losses. A detailed treatment of this method can be found at The Best Bacon System on Earth. I am inviting producers who are interested to interact with me on the process as long as developments will be used for our mutual benefit.

A host of brines has recently seen the light which claims to be natural and nitrite-free. I remain very sceptical about these and refer you to my articles, The Quest for Nitrite Free Curing and an older article, Nitrite Free Bacon: Barriers against Clostridium botulinum

Finally

This review is done from the perspective of a commercial high throughput bacon plant. It, however, paints a rich picture and most of what is regarded as “artisan” today has been the way that large throughput factories of yesteryear have done it. In years to come, how bacon was cured even when we embarked on our current bacon project in 2008 will be regarded as “artisan curing” as we have seen the transition to moulds or grid curing over the last 10 years.

Consumer demands, perceptions and technology will remain the driving force behind this industry.  Many aspects will have to be added to this review article such as changes to health concerns which altered brining technology. I addressed most of these matters in this complete work.

I think back over the many years I have been engaged in this most glorious art and I realise that I am a fortunate man!  My deal La’tjie!  My prayer for you is that you too will find something insanely exciting to build your life around! The question still remains if the curing of bacon taught me the real secret of life? Through my quest, I am living a fulfilled and productive life, yes! That subject I have explored in great detail, but what about the link with what is fixed and eternal? Will meat curing allow me to touch the face of God? There is the most interesting answer to that question but its late and this letter is already very long, The answer to that question must remain till next time!

Just a few more days and both you and Tristan are with us!

Lots and lots of love from Cape Town,

Dad and Minette


Further Reading

Reaction Sequence: From nitrite (NO2-) to nitric oxide (NO) and the cooked cured colour.


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Images

Figure 1:  Founders of bacon plant:  http://www.elmswell-history.org.uk/arch/firms/baconfactory/article2.html

Figure 2:  Stitch pumping, http://www.suffolkheritagedirect.org.uk/resources/tours/made-in-suffolk.html


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