Chapter 12.01.2: Mild-Cured Bacon and the Curers of Wiltshire

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.

* A note on this letter. I searched for this information for almost seven years. I had various clues that such an invention was made, but for years could find no details of it or any information related to its invention.  I knew the system was called “the Danish Method”, but was this the same as tank curing or the live brine system? Was the invention Danish, and if not, who invented it and when? Here I provide all the answers. Mild-Cured bacon is dealt with across two chapters, the previous chapter, William Oake’s Mild-Cured Bacon and this one, Mild-Cured Bacon and the Curers of Wiltshire. The bulk of the information is given in the previous chapter.

Mild-Cured Bacon and the Curers of Wiltshire

December 1990

When I was in Denmark, I wrote a letter to my family back in Cape Town where I told the story of how Uncle Jeppe introduced me to Mild Cured bacon, invented by William Oake in the 1830s. Since I wrote that letter other facts came to light which must be added to the story of Mild-Cured Bacon. When I put the letters together in a book form for my kids in 1990, I added the following additional information.

The Dissemination of knowledge of Chemistry in 1830

In my letter about Mile Curing, I mention that William Oake could have learned about the modern trends in Chemistry at that time from reading rooms in Antrim, Ireland. An example of the dissemination of such knowledge was Liebigs Annalen, his journal on organic chemistry which he started to publish in 1832 with Friederich Wöhler.

It is of course unlikely that Liebig’s Annalen der Chemie was widely available in reading rooms or libraries in Antrim, Ireland in the 1830s. The journal was first published in 1832 and it is unlikely that it would have been widely distributed or easily accessible in a remote location such as Antrim at that time. Additionally, access to scientific journals and publications would have been limited in the 1830s due to the cost and difficulty of distribution. In the 1830s, the most likely places for individuals to study chemistry in Ireland were at universities in the larger cities such as Dublin and Cork. The study of chemistry at universities was still in its infancy, and the curriculum was not yet well developed. A few of the notable figures in chemistry in Ireland during this time period were Robert Kane, who was a professor of chemistry at the Catholic University of Ireland in Dublin and Thomas Thomson, who was a professor of chemistry at Trinity College in Dublin. Kane was known for his work in applied chemistry, particularly in the fields of metallurgy and mining. Thomson was known for his work in analytical chemistry and his textbook “A System of Chemistry” was widely used in universities in the United Kingdom.

Despite the fact that at this time, the discipline of chemistry was undergoing volcanic developments and changes, the knowledge permeated the world slowly which would account for the unfortunate inclusion of Sal Prunella mild cured bacon. The fact that Oake was a trained chemist with access to much of the most recent thinking was enough for him to be aware of the basics of chemistry required to industrialise the process. The industrialisation of other industries based upon a more complete understanding of the underlying chemistry of the processes was happening all over the world at this exact time.

The Wiltshire Cureres and the Use of the Old Brine and Sal Prunella

Pale bacon, most likely resulting from the use of Sal Prunella became the norm by the mid-1800s. It explains the introduction of pale-dried bacon by Harris in the 1890s (Chapter 13.06.00: Harris Bacon – From Pale Dried to Tank Curing) and it probably also becomes a very strong argument that Harris did not fully adopt the Mild-Curing system or the progression by other Wiltshire Curers only till after the last few years in the 1800s or possibly even the opening years of the 1900s.

Even though the practice of reusing old brine was already described in 1830, possibly as early as 1825, it is still a far cry from the complete Mild Curing or the later Wiltshire Process. There can be no doubt that the Wiltshire curers completed the rest of the development that started with the work of William Oake by omitting sal prunella and reverting to the use of saltpetre only in the latter part of the 1800s. The reused old brine itself develops an exceptional preserving power. These curers were able to harness without explaining it, something that a friend of Jeppe, Dr Polenski was the first to observe and explain. I wrote a letter dedicated to the information on dr Polenski. (The Polenski letter)

The reason why the Wiltshire brine becomes a powerful preservative is the fact that it relies on nitrite and not nitrate. Saltpeter is nitrate and is not a very good preservative, but when it changes into nitrite through the process of reduction we described in The Curing Molecule, it becomes a potent preservative. Bacterial reduction of saltpetre (nitrates) to nitrites in the old brine would have caused the curing of subsequent batches to be sped up considerably. This is the reason why boiling the old brine after it was used a few times, as was done in the brine of Catherine the Greats brine was not a good idea as it kills the bacteria. Westphalia hams were famous for their use of the Empress of Russia’s brine from a time before it was introduced in Ireland and the cold smoking process, which was unlike anything being done at the time when “chimney smoking” was the order of the day.

The problem with William Oakes system was his inclusion of Sal Prunella which contained a strong preservative which would have also killed the bacteria resulting in the same thing as one would boil the brine namely the killing of the bacteria which would result in saltpetre remaining nitrate and not converting to nitrite and without nitrite present, nitric oxide could not form to cure the meat (or colour it). Nitric oxide is itself a powerful preservative as is nitrite and something else in Sal Prunella would have been responsible for preserving the meat without proper colour development. Let’s leave the details for a bit later when I deal with Sal Prunella in detail.

Sal Prunella

Despite Oake’s invention, progressions were still being made, and from the name it would ultimately bear, Wiltshire Cure, one can deduce that these further developments and refinements probably happened in Wiltshire. The mistake that Oake made was his use of Sal Prunella, but it was an understandable mistake since it was the latest and most modern addition to curing at the time. Sal Prunella also contains sulphate. A more complete description of the manufacturing of Sal Prunella comes to us from the work of Wootton (1910). “Sal Prunella was at one time in high esteem, as it was believed that by the process adopted for making it, the nitre was specially purified. Purified nitre was melted in an iron pot, and a little flowers of sulphur (1 oz. to 2 lb.) was sprinkled on it, a little at a time. The sulphur deflagrating was supposed to exercise the purifying influence on the nitre. The actual effect was to convert a small part of the nitrate of potash into sulphate. It was first called Sal Prunella in Germany from the belief that it was a specific against a certain plum-coloured quinsy of an epidemic character. Boerhaave advised the omission of the sulphur but believed that melting the pure nitre and moulding it was of medicinal value by evaporating aqueous moisture.” (Wootton, 1910; also see Sal Prunella)

Vecht is very clear in his 1894 interview that mild cured bacon is pale (Interview with Aron Vecht 1894). In this interview, Vecht explains that mild cured bacon, despite being far less salty than the old technique, was pale. He recalls, as a young boy in London, how ongoing work was done to incorporate the new curing system into England. The reason for the pale appearance of the bacon produced with this system is, of course, the presence of sulphite would have had an anti-microbial effect. The Wiltshire curers would later remove this from their brine and rely on the bacteria cultures to thrive in the brine, which would convert the nitrate (saltpetre) to nitrite and ensure proper colour formation as well as preservation. With the microbes being retarded or killed by the sulphites, the conversion to nitrites would not take place inside the meat. It is, therefore, entirely possible that the main “keeping” principle in the original Mild Cured system is related to sulphites.

I suspect that sal prunella was often not produced in the way it was described by Wootton (1910). Possibly not in the amount of sulphur added and definitely not in terms of the fact that it had to be heated to the point of the saltpetre becoming a liquid. If they did, it would have converted the nitrate into nitrite, a conversion step that can normally only be done through bacteria unless extreme heat is used, as would be the case if it was heated to the melting point. It means that despite Oake’s invention, progressions were still being made, and from the name, it would ultimately bear the name Wiltshire Cure, one can deduce that these further developments and refinements probably happened in Wiltshire.

I, therefore, doubt that sal prunella was always melted saltpetre. If it had been, the bacon would not have been pale! The resultant product would have been nitrite which does not require bacteria for nitric oxide to form, which in turn, cures the meat. The reaction can be completely based on chemical reactions apart from bacteria. Irrespective of the presence of sulphites, if the nitrates change into nitrites, the meat would have been cured with the characteristic pinkish-cured colour. An entry in the Encyclopedia Britannica, seventh edition from 1911, describes the reaction. “Saltpeter fuses at 339° to a colourless liquid, which solidifies on cooling to a white fibrous mass, known in pharmacy as sal prunella. It is an energetic oxidizing agent, and on this property its most important applications depend. At a red heat, it evolves oxygen with the formation of potassium nitrite, which, in turn, decomposes at a higher temperature.” This fact, along with the fact that the mild cured bacon was pale as described by Aron Vecht (Interview with Aron Vecht 1894) makes me question if the 339° temperature was reached in the production of most of the sal prunella at the time.


Further Reading

The Mother Brine

Chapter 14.04: Wiltshire Cured or Tank Cured Bacon.

Tank Curing Came From Ireland

Westphalia Bacon and Ham & the Empress of Russia’s Brine: Pre-cursers to Mild Cured Bacon


(c) eben van tonder

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Attfield, John (1871) Chemistry, general, medical, and pharmaceutical.

Bacon Curing – a historical review

Belfast News-Letter (Belfast, Antrim, Northern Ireland), 26 Oct 1841, Tue

Blondel-Mégrelis, M. (2007) Liebig or How to Popularize Chemistry. HYLE–International Journal for Philosophy of Chemistry, Vol. 13, No.1 (2007), pp. 43-54. Copyright © 2007 by HYLE and Marika Blondel-Mégrelis

Chemist and Druggist of 1859

Fereira, J..  Treatise of Food and Diet.  Fowler & Wells.  1843.  P 109, Sodium of Chloride

The Mother Brine

Molineux, (editor).  1898.  The Journal of Agriculture and Industry of South Australia, Molineux was the 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.

Tank Curing Came from Ireland

Wootton, A. C.. (1910) Chronicles of pharmacy, Vol. I. Macmillan and Co., Limited, ST. Martin’s Street, London, Richard Clay and Sons, Limited, Bread Street Hill, E.C., and Bungary, Suffolk.


Image Credits:

Robert Goodrich and members of the Salt Cured Pig

Photos of Minette and I taken by myself