Curing is the addition of ingredients such as sugar, salt, spices, sodium nitrate, and sodium nitrite to preserve a food. One of the oldest methods, it is widely used in the production of ham, pork, corned beef, and some other meats. Salt slows the growth of microorganisms by making water less available to them. Sugar counters the hardening effect of the salt. Sodium nitrate and sodium nitrite help meat keep its red colour. Spices are added primarily for flavour. There are many ways in which food can be cured. In some cases substances are rubbed onto the food; soaking or injecting a solution into the food, or by mixing the ingredients with the food are two other methods. Some meat and fish can also be cured by smoking. Wood smoke contains chemicals that slow the growth of microorganisms. Some studies show that curing agents can be harmful; too much salt in a diet can lead to high blood pressure, and sodium nitrite can mix with other chemicals to form nitrosamines, which cause cancer.
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Canning, which is the most common form of preservation, is the sealing of foods into airtight containers, which are then heated to destroy any lingering microorganisms. Before canning, the food must be thoroughly cleaned, and often cut, sliced, or peeled. The process follows five basic steps: filling, exhausting, sealing, processing, and then cooling. One drawback to canning is the heat used in the canning process changes the food's texture, colour, and flavour. Some nutrients are also lost during this process.

The process of freezing removes the heat from food through the use of low temperatures. It slows down the growth of microorganisms and the breakdown of nutrients. Enzymes are not destroyed or inactivated during freezing, so some foods, such as vegetables must be blanched prior to the process. Food may be cleaned, peeled, or cooked before freezing. The most common commercial freezing devices used today are: plate freezers, continuous-conveyor freezers, air-blast freezers, and cryogenic freezers.

Freeze-drying, on the other hand, removes water from the food while it is still frozen. The process is called sublimation. Frozen food is placed on tray in a large vacuum chamber, heated to just below its melting point, causing the food to become sponge-like. Freeze-drying is an expensive process, so despite the fact that it retains flavour and nutrients better than most processes, it is only used on a few foods.

In contrast to freezing, drying uses heat and/or reduced pressure to remove moisture from food. Because microorganisms require moisture to survive, when the moisture is removed they cease to survive, removing the threat of spoilage. The main techniques used in drying include: sun drying, tray drying, tunnel drying, spray drying, pulse-combustion drying, and drum drying.

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Food processed by aseptic packaging sterilizes the food, and then packages it into a sterile container. This process allows food to keep indefinitely without refrigeration. The containers used in aseptic packaging cost less than traditional materials like metal cans or glass bottles, and this method helps to preserve flavour better.

Irradiation is another one of the major preservation methods. Food is treated with ionizing radiation (radiation that produces electrically charged particles). Low doses of radiation kill bacteria and inactivate enzymes, and cause little change otherwise to the food. It can also kill insects, prevent the sprouting of some vegetables, and eliminate some poisonous microorganisms like salmonella and trichinae, which can cause illness. This process also allows for food to have less person-to-food contact, which decreases the possibility of contamination and a need for chemical preservatives. Irradiation is approved by the FDA to help kill/control the insects or microorganisms in different foods, and to slow the ripening process of fruits and vegetables.

Other methods of preservation include: pasteurization (named for Louis Pasteur), fermentation, fumigation, and controlled atmosphere storage. Pasteurization is a rapid heat treatment that destroys harmful bacteria and causes little nutrient damage. Fermentation chemically changes foods to preserve them with the conversion of sugar to alcohol using yeast under anaerobic conditions. Fumigation is the spraying of foods with toxic gases to prevent infestations of insects or other pests. Controlled-atmosphere storage helps to extend storage life of food; most often with the conditions of 92-95% nitrogen, 3% oxygen, and 2-5% carbon dioxide. [2]