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Nitrates and nitrites are chemical compounds containing nitrogen and oxygen that are commonly used in curing meat. For thousands of years, salt was used to preserve food and meat products, but today sodium nitrate, potassium nitrate, and sodium nitrite are the most common preservatives used in processed meats. They are typically added in the first step of the curing process to inhibit bacterial growth; they do this by removing the moisture bacteria could live on and by killing bacteria through dehydration. Sodium nitrate is particularly effective in food preservation and is widely used because it contributes to a longer aging process.
Many recipes that have been handed down through the years call for saltpeter, or potassium nitrate. Most sausage supply companies no longer sell saltpeter, but you may find other commercial products that will achieve similar results, such as Morton Salt’s Tender Quick® mix. It is a fast cure containing 0.5 percent sodium nitrate and 0.5 percent sodium nitrite and is used in some recipes at the ratio of 1 teaspoon per pound of meat or .17 ounces (7 grams).
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When sodium nitrate and potassium nitrate are added, they alter meat products in three ways: produce a lasting red or pink color; leave a salty flavor; and subtly alter the meat’s texture.
When nitrates or nitrites are combined with fresh meat, a series of reactions occur and nitrite is converted to nitric oxide. Nitric oxide combines with myoglobin, the pigment responsible for the natural red color in uncured meat. Together, they form nitric oxide myoglobin, which is a deep red color. This will change to a bright pink normally associated with cured and smoked meat when heated during the smoking process.
As nitrite compounds convert to nitrous oxygen gas, it kills bacteria such as those causing botulism. Just as nitrous oxide gas reacts with hemoglobin in meat, it can react with human blood hemoglobin with toxic effect if the concentrations are too high. Nitrous oxide converts human hemoglobin into methemoglobin, which does not carry oxygen in red blood cells as well as normal hemoglobin does. With less oxygen available for body tissues to function, a condition called cyanosis can occur. The symptoms include a discoloration of the lips and skin, which typically develop a purple or bluish color.
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Some people have sensitivities to nitrates and nitrites — they get migraine headaches or allergic reactions when consuming these substances. In addition, protein amines can combine with nitrates to produce nitrosamines, which may be carcinogenic. This may be influenced by the amine concentration, length of storage, amount of nitrite added during processing, storage temperatures, and cooking methods or the degree of doneness after cooking.
A fatal dose of potassium nitrate for an adult is 30 to 35 grams ingested in a single dose. Sodium nitrite is lethal at about 22 milligrams per kilogram of adult body weight, or about the same amount as potassium nitrate. To reach a lethal toxicity level, an adult weighing 150 pounds would have to consume about 20 pounds of brine-cured meat containing 200 parts per million (ppm) nitrite in one meal. Unless that person’s diet consists entirely of cured meats, it would take extraordinary stamina to eat enough to reach a lethal level. Even if a person could eat the amount of cured meat containing those levels at one sitting, it is likely the salt level, not the nitrite, would be the toxic factor.
Interestingly, a person with a normal American diet consumes more nitrates from leafy vegetables such as celery, spinach, radishes, cabbage, beets, and lettuce than from cured meats with nitrates and nitrites, because these plants readily absorb nitrogen fertilizers used in food production from the soil in which they are grown.
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Considering all this, a 200 ppm level has been set to preserve the antimicrobial power of these compounds while preventing the development of high nitrosamine, or carcinogenic, concentrations. The USDA limits nitrate and nitrite levels in commercial meat products to 200 ppm. This is the grams of nitrate or nitrite times one million divided by the grams of cured meat that it treats. For example, 200 ppm of nitrate for 50 grams of cured meat is equal to 0.01 grams of nitrate (0.01 x 1 million ÷ 50 = 200).
It is difficult to remove nitrates or nitrites from the meat-curing process without increasing the risk of harmful bacteria, particularly botulism, and a thorough discussion of alternatives is beyond the scope of this book. Some sources recommend cooking the product at a high temperature for a short amount of time (since slow cooking at a low temperature can encourage bacterial growth) and then keeping it refrigerated until you eat it. If you decide that you want to avoid nitrates and nitrites when making your own cured meat products, be sure to research your options thoroughly.