Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage while maintaing nutritional value, texture and flavor.
Preservation ususally involves preventing the growth of bacteria, fungi and other micro-organisms, as well as retarding the oxidation of fats which causes rancidity.
Common methods of preserving food include drying, freezing, vacuum-packing, canning, radiation-treatment and adding preservatives. Other methods that not only help to preserve food, but also add flavor, include pickling, salting, smoking and curing.
The oldest method of food preservation is by drying, which removes moisture required for bacterial growth. Smoking is sometimes done in conjuntion with drying. Although not sufficient by itself to permit long term storage of food, smoking adds chemicals that help inhibit microbial growth. Meat is often also cured with salt or sugar, or a combination of the two.
Canning involves cooking fruits or vegetables, sealing them in sterile cans or jars, and boiling the containers to kill or weaken any remaining bacteria. Various foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal fruits such as tomatoes require longer boiling and addition of other acidic elements. Many vegetables require pressure canning.