Bacon Curing – a historical review.
By Eben van Tonder
31 May 2016
The question came up, what is dry cured bacon? A historical review of the curing process yields interesting perspectives.
The Curing Process
Curing is a fascinating 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 rancidity in fat. It lastly gives meat a unique cured taste.
Discovering the curing process and the mechanics behind it was a slow process that took hundreds of years. The object was the preservation of meat for future consumption. Bacon and other cured products, properly prepared, have, however, always been a delicacy as it remains to this day. Today, taste and a visual appeal probably dominates, but ask any outdoor’s person and they will tell you that preservation for future consumption is still a huge factor in the immense popularity of cured meats.
Before the 1600’s meat preservation was done with salt only. Vegetable dyes were used to bolster colour. The practice of salting meat existed in many cultures including the Far East, the Romans, the Celts and the Gauls. (economist.com)
According to the iconic 1975 review article of Binkerd and Kolari about the history and use of nitrates and nitrites in the curing of meat, “it appears that meat preservation was first practiced in the saline deserts of Hither Asia and in coastal areas. Desert salts contained nitrates and borax as impurities. However, the reddening effect of nitrates was not mentioned until late Roman times.” (Binkerd, E. F. and Kolari O. E.; 1975: 655)
The first recorded specific account of pork curing is probably found in the works of Cato the Elder who wrote in 160 BCE. 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 ham’s are smoked over juniper and beech wood. The process was probably imported by the Roman gourmets from from Germania. (economist.com)
Salt with a little bit of saltpeter
People discovered that certain salt, for example, sea salt or bay salt, had the ability to turn pork meat reddish/ pinkish and prevented it from turning brown.
Dr. Francois Mellett sent me the following very interesting theory about the earliest discovery of the curing process in a private communication between us on the matter. He wrote, “I have a theory that curing started even earlier by early sea farers: when a protein is placed in sea water, 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 sea water barrels and that the whole process of curing was discovered accidentally.”
Salt naturally contains nitrate and in very rear occasions, even a tiny amount of nitrites. Sea salt has all the minerals and chemical elements of the earth washed into it by rain. Some cultures discovered that particular salts, mined from specific locations in dry regions, had far more of this “special power”, endowed with a peculiar bitter taste and a greater ability to bring about this reddish/ pinkish colour.
This salt came to be known as saltpeter. The “change from vegetable dyes to saltpeter for the coloring or color preservation, respectively, of meat, occurred between 1600 and 1750, probably near 1700.” (Lauer K. 1991.)
This same saltpeter had great use in the production of explosives such as gunpowder and had very productive applications as a fertiliser. It became a widely traded commodity and companies were created around the world who specialised in not just mining and shipping it, but later in manufacturing it. (Hui, Y. H., 2012: 540)
The earliest form of dry curing was done with a mixture of salt and saltpeter, 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 saltpeter. 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 contributes to “maintaining acid and reducing conditions favorable” 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 utilization by microorganisms or the enzymatic systems of the meat tissues.” (Kraybill, H. R.. 2009)
Dry-salt-curing in combination with injection
It seems that the basic definition 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 a certain Mr Morgan, in England, who invented the technique of injecting a liquid brine into the meat in the first place. The motivation was to increase the rate of curing in order to reduce the time required for processing. In temperatures above 20 deg C, pork spoils in three days.
It was important for farmers to cure the meat before a warm snap could allow spoilage organisms to work before the cure was properly diffused through the meat. Later, in industrial plants, the drive for a faster curing time would be cost factors. Increased output with limited and expensive equipment and people.
By injecting a liquid brine into the meat at evenly spaced intervals, the brine would diffuse quicker through the meat. It is also important to state that his interest was the preserving of meat generally for example for long sea voyages and not the curing of meat by farmers. The application of his method of injection, however, found its way into many homes and factories around the world.
Edward Smith writes in his book, Foods, in 1873 and account the events of “Mr Morgan [who] 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] presided.” (Smith, E, 1873: 35)
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 observations from the article is the date of 1870. By this date he is referred to as “Dr. Morgan”, cluing us in about the time-line of Morgan’s life.
The second 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, p4)
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 later, in 1871, Yeats reports on a certain “Professor Morgan in Dublin, who has 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 saltpetre, 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 probably the same Morgan that Smith reports on who by 1871 became a professor in Dublin. He has by this time apparently abandoned his arterial injection method for a more general injection into the muscle, even though arterial injection still prevails in certain butcheries.
Notice, as a matter of interest that he used the same basic brine mix of salt, water, saltpeter, sugar, monophosphoric acid and spices. This, together with the similarity in surname makes me quite certain that Mr. Morgan and Prof. Morgan is the same person. In itself, this is an example of perseverance! In 1854 his arterial injection was met with skepticism where Yeats reports in 1871 that the Admiralty viewed his improved method with great interest.
It is reported today by some bacon curers that they use 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 the famous Harris from Calne in the United Kingdom used injection with their dry cured bacon from 1843.
After it has been dry-cured, the meat is 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. Care should also 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)
Brine-soaking followed dry-salt-curing. Again, note that dry or wet curing is defined by what the meat if left in to cure and not what is injected into the meat. The process is also relatively slow and meat pieces are placed in a mixture of salt, saltpeter 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)
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 down-side 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)
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 Denmark. Before we get to that, we have to first look at 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 also had the benefit of being stored in the cure and being safe from flies and other insects.
In the 1800’s, 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. Afterward, 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 salt-petre. 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, saltpeter, sugar mixed in water. The role of the sugar was to break the hard salt taste.
Barrel pork would remain an important curing method throughout the 1700’s and would make a spectacular return almost a 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 act as a cover brine. It would remain in the cover brine the prescribed time before it is removed and smoked.
Boiling of the brine
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 are 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. (The Complete Grazier, 1830: 304)
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)
Remember that wet-cure is more expensive than dry cure unless the brine is re-used. Our farmer states that brine is re-used “with advantage”. Before it is re-used, the old brine must be boiled first and water and the other ingredients must be added proportionately. (The Complete Grazier, 1830: 304)
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 Danes use wet curing and injection together. They inject a mixture of salt and saltpeter into the muscle and leave the injected muscle in a mother-brine as the cover brine. This actually gives them the best of both worlds.
The nitrite which they get from the mother brine would immediately go to work and start curing the meat while the nitrate injected as saltpeter (potassium nitrate) would, over time, be reduced to nitrite and continue to do the curing work even long after is has been removed from the cover-brine.
The method is simply ingenious and the only thing more effective would be if we directly add sodium nitrite to the brine in a fixed proportion. At this point sodium nitrite is however very expensive and regarded with great skepticism by the general public who sees it as a drug for heart conditions and as a specialty product used in the dye industry.
Wet curing is not only if a brine (a salt and water mixture) is used, for example, as injection-brine and dry-curing is not when salt only is used. The history of curing techniques paints a rich picture of salt-only dry-curing, brine injected dry-curing, wet curing with no brine injection, wet curing with brine-injection, barrel pork curing, tank curing and finally multi-needle injectors and vacuum tumblers in use today. There are overlaps in the terminology and the practices used so that an exact definition is probably not possible.
Binkerd, E. F. and Kolari O. E.. 1975. The history and use of nitrate and nitrite in the curing of meat. Fd Cosmet. ToxicoL Vol. 13. pp. 655–661. Pergamon Press 1975. Printed in Great Britain
The Complete Grazier. 1830. Fifth edition. paternoster Row. Baldwin and Cradock
Holland, LZ. 2003. Feasting and Fasting with Lewis & Clark: A Food and Social History of the early 1800’s. Old Yellowstone Publishing, Inc.
Hui, Y. H.. 2012. Handbook of meat and meat processing. Second edition. CRC Press.
Kraybill, H. R.. 2009. Sugar and Other Carbohydrates in Meat Processing. American Meat Institute Foundation, and Department of Biochemistry, The University of Chicago, Chicago, Ill. USE OF SUGARS AND OTHER CARBOHYDRATES IN THE FOOD INDUSTRY. Chapter 11, pp 83–88. Advances in Chemistry, Vol. 12. Publication Date (Print): July 22, 2009 . 1955
Lauer K. 1991. The history of nitrite in human nutrition: a contribution from German cookery books. Journal of clinical epidemiology. 1991;44(3):261-4.
Smith, Edwards. 1873. Foods. Henry S King and Co.
Sydney Morning Herald, 1 March 1870, p4
Yeats, J. 1871. The technical history of commerce; or, Skilled labour applied to production. Cassell, Petter, and Galpin
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