It’s eaten for breakfast (with a fried egg), put on burgers, in salads, with Brussels sprouts, crispied up, candied, or slothered with maple syrup. What we’re talking about? Bacon! Somehow, many people seem to be obsessed with bacon. About time we dig deeper into bacon. Because, yes, we know bacon comes from pigs (we do know that don’t we?). But then, what happens in between it being a pig and a crispy slice of bacon on your plate?
An important characteristic of bacon is that it has been cured (and oftentimes smoked as well). Thus bacon is no raw meat, it has been processed to a certain extent.
Curing is a way of preserving meat. The most basic cure is by covering a piece of meat in a lot of salt (often containing nitrite, we’ll come back to that later) and leave to rest for several days. During the curing process salt will go into the meat and some moisture will be pulled out through osmosis. This is how most bacon used to be made when it was still made at home in farms. Bacon could also be smoked after this cure, which was common practice as well. Smoking would make bacon even better to preserve by drying it out slightly. The smoke itself probably has a preservative effect as well, however, it still isn’t completely clear how that works.
The flavour of bacon can be improved by adding other ingredients to the salt mix which is used to cure. Often sugar is added as well, or spices.
The reason curing meat actually preserves the meat has several reasons. The salt rub pulls out water from the meat, drying the meat slightly. It also increases the salt concentration. Most micro organisms cannot grow at these increased salt concentrations, thus it prevents the meat from spoiling. At the same time, the salt toughens up the meat, making it firmer through the interaction with proteins.
Commercial processing, brine injection
Nowadays, most bacon isn’t made by rubbing a piece of meat with salt and leaving it to rest for several days. This is a very labour intensive process, thus nowadays, most products are made using a wet cure. In a wet cure salt is dissolved in water, together with sugar and possibly other flavours. The meat is placed in this brine for a couple of days, before being taken out and maturing.
Even this method has been made more efficient again. Nowadays, meat is often injected with the brine. This helps the salt to migrate into the center of the meat a lot faster, greatly shortening the time required to mature. It might be as short as only a few hours instead of days.
Bacon and nitrite
As mentioned above, the salt used for curing meat generally contains nitrite as well. It depends on the country, but in various countries a product may not be legally cured without the use of nitrite in the salt.
Nitrite is a molecule with the following chemical formula: NO2–. It is an ion and is generally used as a salt, for example: NaNO2. Instead of using nitrite, in some cases it it also possible to use nitrate, often present as KNO3. Nitrate can convert into nitrite, but this takes time and has to be done by bacteria present in the meat. Thus, in modern production the direct use of nitrite is preferred, although nitrate can be used if nitrite formation over a longer period of time has to take place for instance.
Nitrite itself is dangerous for humans when consumed in large quantities. This is why nitrite is never sold in its pure form for food applications. Instead, it is always mixed with salt, ready to be used in a brine or in a dry cure. If a manufacturer would overshoot the product would be too salty as well, thus not consumed by the consumer.
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History of use of nitrate
I was curious to know whether the use of such a chemical component as nitrite was known for a long time in history or whether it’s a recent discovery. I found that the use of nitrate (although people didn’t know it was nitrate) is several centuries old, if not more. A common source of nitrate at the time was salpeter which could be found in the earth.
It seems that the existence of nitrite was also known from at least the 19th century. However, it was related to death and danger, thus not used for curing meat. Only in the 20th century manufacturing methods became suited to make nitrite on a large scale for curing meat.
Role of nitrites – safety
Since nitrites can be dangerous for humans, why are they used? There are two main reasons for this: colour and food safety. Yes, using nitrites in a correct way greatly improves food safety of cured meats. When nitrites are used correctly there doesn’t seem to be a danger to health (although they have been linked with causing cancer, but I won’t go into detail of that here).
The main reason for using nitrite is to prevent the growth of Clostridium botulinum. This bacteria can make a component which is highly poisonous for humans. Even very very small amounts can kill humans. Thus food producers want to prevent the presence of the bacteria at all times. However, C. botulinum happens to be very heat resistant, especially its spores. So a simple pasteurization treatment won’t kill it. Spores are a way of bacteria to survive in very harsh situations. Spores can survive in extreme conditions for quite some time. Once the conditions are less harsh again, they’ll start living as bacteria again, in the case of C. botulinum, also making poison again.
Cured meats undergo a mild heat treatment, by far not sufficient to kill off spores. Thus, to keep the meat safe, nitrite is required. When using nitrite and high salt concentrations, practically no bacteria can grow in the meat anymore.
Colour of cured meats
Cured meats have a pinkish colour, pretty different from that of fresh meat. Fresh meat can be dark red, purple and will turn brown when in contact with oxygen. The fact that this doesn’t happen to cured meat can be attributed to the use of nitrite.
As discussed in my post on the colour of meat, the myoglobin protein plays a central role in the colour of meat. Myoglobin can react with oxygen causing it to turn brown. However, nitrites can also interact with myoglobin to form metmyoglobin. Metmyoglobin is a brown component, meat that has been cured but not yet heated still looks brown. Heating the meat will initiate a transformation to a more stable pink colour nitrosomyochromogen. This pink color isn’t stable forever, under the influence of light and oxygen it can slowly convert to a light brown colour again.
Enjoy your (English) breakfast and have a look at your bacon, what type are you eating (and which do you like best)?
I found a great and very interesting deep dive from Bloomberg on the growth and history of bacon. It’s a great read if you’d like to learn more on American bacon. I learned more about the English breakfast and the different bacon types here.
For those reading Dutch, here’s a nice report on the use of nitrites. For the english speaking, there’s also a report from the FAO. And there’s a university website explaining curing meat in more detail.