Curing refers to various
food preservation and
flavoring processes, especially of
meat or
fish, by the addition of a combination of
salt,
sugar,
nitrates or
nitrite . Many curing processes also involve
smoking.
Chemical actions
The chemical actions of curing are highly complex with slow reactions of proteins and fats through
autolysis and
oxidation. These reactions can be driven by auto-oxidation alone though it is typically accompanied by enzymes in the curing food as well as beneficial fungi and bacteria.
To enable these slow curing reactions and prevent rapid decomposition through rotting, water is extracted from the food and the food is made inhospitable to microorganisms. This is usually done by applying
salt and a combination of other ingredients to cure the food.
Salt
Table salt, which consists primarily of
sodium chloride, is the most important ingredient for curing food and is used in relatively large quantities. Salt kills and inhibits the growth of
microorganisms by drawing water out of the
cells of both microbe and food alike through
osmosis. Concentrations of salt up to 20% are required to kill most species of unwanted bacteria.
Once properly salted, the food's interior contains enough salt to exert osmotic pressures that prevent or retard the growth of many undesirable microbes.
Sugar
Although often used in curing to give a pleasant taste, sugar can also be used to encourage the growth of beneficial bacteria such as those of the
Lactobacillus genus.
Dextrose or
sucrose that is used in this fashion
ferments the food.
As the unwanted bacterial growth is delayed, the salt tolerant lactobacillus outcompetes them and further prevents their growth by generating an acidic environment (around 4.5
pH) through production of
lactic acid. This inhibits the growth of other microbes and accounts for the tangy flavor of some cured products.
Nitrates and nitrites
Nitrates and nitrites not only help kill bacteria, but also produce a characteristic flavor, and give meat a pink or red color.
Nitrate (NO
3−), supplied by e.g.
sodium nitrate or
potassium nitrate, is used as a source for
nitrite (NO
2−). The nitrite further breaks down in the meat into
nitric oxide (NO), which then binds to the iron atom in the center of
myoglobin's heme group, reducing oxidation and causing a reddish-brown color (nitrosomyoglobin) when raw, and the characteristic pink color (nitrosohemochrome) when cooked.
The presence of nitrates and nitrites in food is controversial due to the development of
nitrosamines when the food, primarily bacon, is cooked at high temperatures. The nitrate and nitrite compounds themselves are not harmful, however, and are among the
antioxidants found in fresh vegetables. (National Academy 1981) The usage of either compound is carefully regulated in the production of cured products; in the United States, their concentration in finished products is limited to 200 ppm, and is usually lower. Finally, they are irreplaceable in the prevention of
botulinum poisoning from consumption of dry-cured sausages by preventing spore germination.
A 2007 study by
Columbia University suggests a link between eating cured meats and
chronic obstructive pulmonary disease.
Nitrites were posited as a possible cause.
Smoke
Smoking adds chemical compounds to the surface of an item which affect the ability of bacteria and fungi to grow, inhibit fat oxidation (and thus rancidity), and change flavor.
History
Historically, people around the world have cured meat, in order not to waste valuable food, and to insure against poor harvests or hunting seasons. Although a salt-rich diet is currently implicated in risk for heart disease, in the past food shortage was a greater problem.
Salt cod, which was air-dried in cool northern Europe, was a civilization-changing food product, in that a bountiful but perishable food supply could be converted to a form that allowed for wide travel and thus exploration. Salted meat was widely used as a food source on ships during the
Age of Sail, as it is non-perishable and easily stored.
Eric Newby wrote that salted meats consisted of the majority of shipboard diet even as late as his cruise aboard
Moshulu (which lacked any refrigeration) in 1938.
Salted meat and fish are commonly eaten as a staple of the diet in
North Africa,
Southern China and in the
Arctic.
Some cured food products
- Cured vegetable products:
See also
Notes and references
- McGee, Harold. On Food and Cooking (revised). New York, NY: Scribner, 2004. ISBN 0-684-80001-2
- Bertolli, Paul. Cooking by Hand. New York, NY: Clarkson Potter/Publishers, 2003. ISBN 0-609-60893-2
- National Academy of Sciences - National Research Council Academy of Life Sciences. "The Health Effects of Nitrate, Nitrite and N-Nitroso Compounds". Washington DC: National Academy Press, 1981.
