by Eben van Tonder
23 November 2022
I updated my review of curing systems by adding a section on the mechanism behind salt-only curing. It just so happens that the South African retailer, Woolworths launched their range of bacon with the claim “contain no nitrites.” In discussing salt-only-curing, I used them as an example and evaluated their claim. Here is the extract from Bacon Curing – a Historical Review.
The Mechanism of Salt-Curing
For years I never seriously looked at salt-only-curing. Yes, its mechanism is well known, or so I thought! The salt reduced the water in the meat which retards the micro activity and meat breakdown (enzymatic) while L-Arginine slowly oxidises to L-citrulline and nitric oxide and nitric oxide cures the meat.
The booklet that Edward De Bruin, my South African friend living in New Zealand sent me (Methods of Meat Curing, 1951, US Dep of Agriculture) reported that in a survey done in the early 1950s, it was found that 37 percent of the farmers used dry curing. The curing agent they used was salt only. The author describes it as follows, “a fine grade of sack salt or table salt applied to hams, shoulders, and bacons. All the salt was applied at one time by about one-half of the farmers, 10 pounds (4.5kg) of dry salt per 100 pounds (45kg) of meat being used. The liquid extracted from the meat during cure was not permitted to accumulate. Curing temperatures ranged from 20° to 50° F. (-6°C to 10°C), the average being about 40°F (4°C). Most hams weighed 20lb (20kg), 25lb (11kg), or 30lb (13.6kg) : shoulders and bacons weighed 20lb (20kg) pounds. The hams were cured for 1½ days per pound : shoulders and bacons, 1¾ days. About 50 percent of the farmers smoked their meat. Prior to smoking 3 to 1 days in hickory smoke, the meat was washed. The meat was stored in a dry, cool room with some air circulation. Consumption began immediately after the meat was cured and smoked, although some meat was stored for 9 months.”
The method was simple and effective. It took around 30 days to cure the meat and this was the problem. All subsequent curing methods from time immemorial, which is the subject of this work, were done to reduce this time. With the 20:20 hindsight we have peering back over aeons of time, we realise that what they were looking for was other ways to speed up the production of Nitric Oxide which is the curing molecule with its reddening effect on the meat and its broad spectrum antimicrobial activity.
The earliest progression from salt-only curing was the addition of nitrate directly through saltpetre and the oxidation of ammonium. This article sets out this progression. Following World War 1, nitrite was added directly and right from the start this was controversial. The motivation for the change from nitrate to nitrite was the availability of nitrate in a war situation and secondly, the speed of curing with nitrite curing being much faster than nitrate curing. Since that time, and especially from the 60s and 70s, the curing industry tried to find a system that does not rely on nitrate or nitrite. I believe this was done based on an inadequate understanding of the role of nitrate and nitrite in human health but it’s a discussion for another time. (The Truth About Meat Curing: What the popular media do NOT want you to know!)
When the industry found this to be impossible (curing without nitrate or nitrite), a trend began where some denied its inclusion in meat or at least tried to hide it. They did this by using an ancient method of curing where plants and fruits are used, naturally high in nitrate and nitrite but label declaration legislation does not necessitate you to declare all the chemical species naturally found in the plant matter. So, it is still nitrate and nitrite added to the meat which produces the nitric oxide which cures the meat, but using this strategy, producers did not have to include nitrate or nitrite on their labels.
Using this method of curing results in a healthier product due to the inclusion of minerals, vitamins, antioxidants and other beneficial plant constituents but to claim no-nitrite/ nitrate curing is false. A contemporary example of this may be the recent launch of Woolworths in South Africa.
Woolworths in South Africa launched a range of bacon recently which they claim to be cured without nitrite. They state on their packaging that their bacon is cured “using a combination of fruit and spice extracts without compromising on flavour, texture or colour, and it contains no nitrites.” The question is what “contains no nitrites?” Is it the bacon that contains no nitrites or the curing brine?
Maybe they added these indirectly through plant matter which, in the end, is exactly the same thing as adding it directly with a major difference being that adding it through plant matter makes the process uncontrolled – meaning they can’t control how much they add as opposed to the method of adding nitrate and nitrite directly which enables you to reduce the amount of ingoing nitrate and nitrite to the smallest possible ratio which is the “safest” way of doing it if you believe that nitrates and nitrites are bad for your health (an assumption that I do not subscribe to, see The Truth About Meat Curing: What the popular media do NOT want you to know!) Whatever the consequence of adding it through plant matter, claiming “no nitrites” will be a blatantly false statement and I don’t believe this is what they are doing for one moment.
Of course, the “contain no nitrites” may mean that they took care to remove all residual nitrites from the bacon after it was cured. Residual nitrites are what is left in the bacon after curing. I will argue that nitrates and nitrates is not a big deal (The Truth About Meat Curing: What the popular media do NOT want you to know!) but I understand many consumers still have a negative perception of nitrites and if the products are not formulated right, it poses a problem. Residual nitrites can be reduced dramatically by employing a range of processing techniques and through bacteria. Staphylococcus xylosus and Staphylococcus carnosus have, for example, been shown to be also able to reduce the residual amounts of nitrates and nitrites (Neubauer and Götz, 1996; Gøtterup et al., 2007; Mah and Hwang, 2009; Bosse et al., 2016). Woolworths is a quality-driven company their statement, “contain no nitrites” means that they used nitrates and nitrites but removed any traces of it before its made available for sale, I applaud them for their work! There is a small technical matter related to the chemical generation of nitrate from nitric oxide in a meat system and the fact that nitrite will soon be generated through bacterial action which calls into question if one can call any cured meat system 100% free from nitrites, but that is a question for another forum and it is possible with the right approach.
All this is an example of how the industry is grappling with the fact that nitrates/ nitrites are used. Before any of this became an issue in the world, there was curing with salt only. It would seem to me that at the heart of the entire move away from salt-only-curing was the fact that we fundamentally missed the role of microorganisms with the ability to react with protein and to create nitric oxide which then cures the meat. Well, we “missed” it because it was so hard to see nor did we have the technology to identify and isolate certain bacteria with this ability, nor did we understand what bacteria need to be effective by way of nutrition.
We had glimpses of this from the world of salt-only curing! The mechanisms underpinning salt-only curing are only emerging now as a powerful method to cure meat without the use of nitrate or nitrite, directly or indirectly. Let me say it like this. Now that we are working out the mechanism of salt-only curing, we discover ways to do it as quickly as is done with nitrite curing. Despite many years of intense research into meat curing, it is remarkable that we are only now starting to understand how the oldest form of curing works.
Proteins and lipids or fats in meat tissues are degraded mainly by enzymes which are also present in the meat during the ripening of the hams/ bacon but the breakdown of proteins and fat cells is also achieved through bacteria (Flores and Toldrá, 2011) and they play a direct role in curing in salt-only systems. Morita et al. found that Nitric Oxide formed in salt-only curing systems is achieved from L-arginine due to nitric oxide synthase (NOS) in either Staphylococci or Lactobacilli. (Morita et al., 1998 and quoted by Gasasira, et al, 2013) Another study on the production of cured meat colour in nitrite-free sausages by Lactobacillus fermentum showed that nitrosylmyoglobin (a form of the meat protein, myoglobin, formed during curing) could be generated when the bacteria, Lactobacillus fermentum AS1.1880 was inoculated into the meat batter, and the formation of a characteristic pink colour with an intensity comparable to that in nitrite-cured sausage can be achieved using 108 CFU/g of the culture. In other words, bacteria, in a salt-only curing system can directly achieve what nitrite curing would later accomplish.
Despite the fact that even in the 1950s salt-only-curing was the biggest single way that bacon was produced on farms in the USA, I am going to look at two important salt-only-cured hams that have been the subject of research which elucidated the mechanisms underpinning salt-only-curing and to illustrate that the key, understanding the mechanism behind salt-only-curing, is bacteria. Microorganisms drive the process!
Parma ham is traditionally produced using only sodium chloride without the addition of nitrate or nitrite and develops a deep red colour, which is stable also on exposure to air. It has been shown that bacteria are responsible for the creation of nitric oxide without nitrate or nitrite which then cures the hams. Fascinatingly, despite the fact that we know that bacteria are responsible for the creation of nitric oxide which leads to nitrosylated heme pigments, the identity of the pigment of Parma ham has not been established. In one study, the stability of the pigment isolated from two different types of dry-cured ham (made with or without nitrite) was compared to that of the NO derivative of myoglobin formed by bacterial activity. Heme pigment from Parma ham made without nitrite was more stable against oxidation than the pigment from dry-cured ham with added nitrite.” (Møller and Skibsted, 2001) This is a most fascinating discovery! Further, heme pigments extracted from Parma ham and a bacterial (Staphylococcus xylosus) formed NO-heme derivative and have similar spectral characteristics (UV/ vis spectra and ESR).” (Møller and Skibsted, 2001)
In China, Nuodeng ham is a dry-cured ham, traditionally made by Bai ethnic people in the Nuodeng village, Dali, Yunnan Province. As part of the production process, they use mineral-rich local salt reserves, and distilled corn liquor and rely on the favourable climate. From these hams, Kocuria rhizophila was isolated (Shi, 2021) and is probably responsible for the formation of the cured colour.
I can give many more examples. Dry-cured, long-cured or salt-only systems are in part enabled by bacterial action where the meat itself is fermented, nitric oxide is generated and the meat is cured. I return to this subject in the very last section of this article under the heading Bacterial Fermentation Curing. Woolworths in South Africa may very well rely on this mechanism of curing their bacon which is the only system where they can make the claim that nitrite is not present. If one would test their cure or their bacon at any time immediately following curing and in the time that it spends on the retail shelf or in the consumer’s refrigerator and nitrite is found, it will make their claim that no nitrites are present, false.
Besides the option of using plant matter that contains nitrate or nitrite, they could of course create the cured colour with proteins outside the meat environment and infuse these into the meat, which I doubt is what they are doing. They could use nitrite to cure the meat directly or indirectly and add bacteria that eliminates all nitrites post curing which is possible, but I would think improbable. The last option is that they could use nitrites at a level below 10 parts per million which will still cure the meat but is undetected in certain methods of testing for nitrites. The challenge will be that at those low levels the nitrite offers little protection against dangerous microorganisms but I notice that they add rosemary extract which could bolster this protecting mechanism. If this is what they are doing, it would unfortunately again make their claim of “contain no nitrites“, false. If, and I am by no means suggesting they are doing this, a clue would be if they are very sensitive to environmental exposure to nitrites during production as this could push the levels of nitrite in the bacon into the levels which are “detectable”.
The last option would be “underhanded” and with a company like Woolworths, there is no chance that they employ such a strategy. Friends of mine work in their meat department both in the compliance as well as operational departments and they would never be a party to anything not completely truthful. Well done to Woolworths then on your product which can only be using some form of fermentation.
Bacterial fermentation of meat is probably the closest one will ever get to a no-nitrite system which is a spectacular return to salt-only curing. Working out how to do it is, as the saying goes, the million-dollar question and if Woolworths found the way, I salute you! As far as our consideration of curing systems goes, our first consideration of curing, namely salt-only, will also be our final consideration under Bacterial Fermentation Curing. In between these two is the most fascinating story never told!
As far as Woolworths’ “contain no nitrites-bacon” is concerned, maybe they can be more specific about which one of the options they refer to when they make that claim.
Extract from Bacon Curing – a Historical Review.
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