Curing is essentially the addition of sodium nitrite or sodium nitrate to a food. The salts can be mixed in, brined, or injected into meats. Nitrite salts have preservative effects against Clostridium botulinum. They have been used since the early 20th century. These same salts change both meat color and can change meat texture.
Curing meats, poultry, or seafood is permitted under the US FDA model Food Code as a specialized process (3-502.11) with a variance approved food safety plan. The act alone of adding the curing salt (nitrite or nitrate) to a food is a possible hazard. In addition, some processes use curing salts to limit the hazard of C. botulinum while the food is further processed in the temperature danger zone (41-135F) such as smoking. There are other considerations as well. Bacon has USDA limits on the amount of residual nitrite to minimize the potential for any formations of toxic nitrosamines.
I would like to introduce a new term: “culinary curing“. This term describes the addition of curing salts for culinary reasons only. The food item containing the curing salts is held refrigerated (frozen) or immediately cooked. The curing salts are not needed for any antimicrobial or anti-Clostridial properties. The suggested culinary use level is 75 ppm for all uses (direct addition, brine, or dry rub).
There are “natural” cures available. These are various mixtures of celery powder and sea salt that naturally contain nitrate. One manufacturer uses bacterial cultures to microbially convert nitrate into nitrite. This is then packaged and sold as “Vegstable 504™” (no endorsement implied). Some have commented this product caused unacceptable off flavors (not personally tested). The USDA’s position on this product is that it cannot be used as a “curing” salt for food preservation (protection from Clostridium). They list it as a flavor. Using that interpretation, the FDA may also agree its a flavor meaning its addition to a food would NOT require a HACCP plan or specialized process documentation under the US FDA model Food Code.