Traditionally when a pig was killed, the carcass had to last the family for many months. Raw meat quickly goes off as bacteria from the skin and guts break down the sugars in the meat before attacking the proteins, leading to slime production and a putrid smell. People discovered that by rubbing the carcass with saltpetre and keeping it in an airy place (once the gut, lungs and other soft tissues had been removed, of course) the meat stayed edible for a lot longer, as well as tasting good.

What happened during this process was that the sodium nitrate in the saltpetre became converted to nitrite by the natural flora of microbes present, mainly a type of bacterium called Micrococcus. Nitrite acts as a preservative and inhibits many different bacteria, including food poisoning organisms. Nowadays nitrates have been replaced by nitrites and dry cures are only used for specialist products.

Modern cured ham is usually made by injecting curing brines into whole muscles, or by soaking cut-up meat in a vat of brine. The brines contain sodium nitrite, salt and sometimes other preservatives such as ascorbate. The salt reduces the water activity, which slows down the rate at which microbes grow. Other ingredients include sugar, spices and phosphate which contribute to the flavour and juiciness of the product.

Once the cure is complete the ham might be smoked before it is cooked. Smoking over burning wood chips not only adds flavour to the ham but also helps the product to keep longer due to the antimicrobial activity of components of the smoke. Hams are usually cooked by boiling or by steam under pressure, before being cooled in cold water or in the air and then packaged. Some hams are packed whole, others are sliced first. Such ham is kept refrigerated until the point of sale. Some hams are canned, which means they receive a thorough heat treatment in the container which destroys all microbes including any spores. These can be kept at room temperature provided the seal is unbroken.

Air-cured hams like Prosciutto di Parma from Italy and Serrano from Spain are made by traditional processes and are a speciality of mountain regions. The pigs are often specially bred and even their treatment before slaughter is carefully controlled. The hind legs of the carcass are removed, chilled and trimmed, and then covered in salt for 2-3 weeks. This draws off water to levels at which microbes cannot grow. The salt is then removed and the hams are rested before any remaining salt is washed off and they are hung up to dry in a carefully controlled atmosphere. This pre-curing stage takes about 3 months. For the final maturing or curing period of up to 18 months, the hams are moved to special drying rooms where the characteristic flavours and aromas develop. In Italy the whole process is regulated by law and only the product from a certain area can be sold as Parma ham.

Air-cured hams are either sold whole or are sliced and packaged in hygienically controlled conditions to prevent contamination by micro-organisms.