In food preparation, curing refers to various preservation and flavoring processes, especially of meat or fish, by the addition of a combination of salt, sugar and nitrate and/or nitrite. Many curing processes also involve smoking. The etymology of the term is unclear, but it is thought to derive from the same Latin cura, -ae, from which the other English meanings are also derived.
Salt inhibits the growth of spoilage-causing microorganisms by drawing water out of microbial cells through osmosis. As the unwanted bacterial population decreases, other beneficial bacteria, primarily of the Lactobacillus genus, come to the fore and generate an acidic environment (around 4.5 pH). The sugar included in the cure is used as food by the lactobacilli; generally dextrose is preferred over sucrose, or table sugar, because it seems to be more thoroughly consumed by the bacteria. This process is in fact a form of fermentation, and, in addition to reducing further the ability of the spoilage bacteria to grow, accounts for the tangy flavor of some cured products. Concentrations of salt up to 20% are required to kill most species of unwanted bacteria.
Smoking adds chemicals to the surface of an item which affect the ability of bacteria to grow, inhibit oxidation (and thus rancidity), and improve flavor.
Nitrate and Nitrite Compounds Nitrates and nitrites not only help kill bacteria, but also produce a characteristic flavor, and give meat a pink or red color. Nitrate (NO3), in the form of either sodium nitrate or potassium nitrate, is used as a source for nitrite (NO2). 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, preventing oxidation.
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.
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. Historically, peoples 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 and fish are commonly eaten as a staple of the diet in North Africa, Southern China and in the Arctic where they are associated with nasopharyngeal cancer. One study hypothesizes that the actual vector is anaerobic bacteria found in salted fish. (The Scientist 1999)