Most domesticated animals produce large quantities of meat at slaughtering time. During the long centuries before refrigeration, preserving that meat for later use was a major preoccupation for farmers and cooks alike. Salt's value as a preservative is well known, bringing the life cycle of most microorganisms to a sudden halt. Over time, it became obvious that the impurities in some salts made them better than others for preserving meats. By the 19th century, scientists were able to identify those impurities as naturally-occurring nitrates and nitrites.

Many common vegetables, such as celery, naturally contain high quantities of potassium nitrate. It's also found in mineral deposits, where it's been known for centuries as saltpetre. In cured meats, hardy bacteria that can survive at high salt levels break down the nitrate into nitrite, which in turn provides protection against botulism and other dangerous forms of foodborne illness. After this discovery, many food manufacturers began using small amounts of refined nitrites, rather than saltpetre. However, the slow breakdown of nitrates into nitrites improves the flavor of many meats, so purified nitrates are still used in many curing mixtures.

Research in the 1970s showed that under certain circumstances, nitrites could be transformed by heat into potentially carcinogenic nitrosamines. The U.S. Food and Drug Administration and the USDA's Food Safety and Inspection Service subsequently laid out strict limits on the use of nitrites and nitrates in cured meats. A report from the American Medical Association's Council on Scientific Affairs released in 2004 concluded that the levels of nitrites permitted in cured meats in the United States posed no health risk.

As part of the curing solution, nitrites permeate your ham just as the salt, sugar and spices do. Boiling won't remove them, but it's still a beneficial cooking method because it reduces the quantity of sodium -- a more immediate health threat -- in your ham. Boiling your ham, or more accurately simmering it, gives wet-cured or "city" hams a firmer, more appealing texture. Dry-cured country hams are much saltier, and usually require soaking and then simmering before they're ready for table use. It also produces a rich ham broth, which can be used for soups or as a flavorful cooking liquid for vegetables.