Food preservation

Main food preservation methods

Method	Effect on microbial growth or survival
Refrigeration or chilling	Low temperature to retard growth
Freezing	Low temperature and reduction of water activity to prevent growth
Drying, curing and conserving	Reduction in water activity sufficient to delay or prevent growth
Vacuum and oxygen free modified atmosphere packaging	Low oxygen tension in inhibit strict aerobes and delay growth of facultive anaerobes
Carbon dioxide enriched modified atmosphere packaging	Specific inhibition of some micro-organisms by carbon dioxide
Addition of acids	Reduction of pH value and sometimes additional inhibition by the particular acid
Lactic fermentation	Reduction of pH value in situ by microbial action and sometimes additional inhibition by the lactic and acetic acids formed and by other microbial products ''e.g. ethanol, bacteriocins
Emulsification	Compartmentalisation and nutrient limitation within the aqueous droplets in water-in-oil emulsion foods
Addition of preservatives	Inhibition of specific groups of micro-organisms
Pasteurization and appertization	Delivery of heat sufficient to inactivate target micro-organisms to the desired extent
Radurization, radicidation and radappertization	Delivery of ionising radiation
Application of high hydrostatic pressure Pascalization	Pressure-inactivation of vegetative bacteria, yeasts and moulds

Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage to prevent foodborne illness while maintaining nutritional value, texture and flavor.

Preservation usually 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 reduces water activity sufficient to delay or prevent bacterial growth. Smoking is sometimes done in conjunction with drying. Although not sufficient by itself to permit long term storage of food, smoking adds chemicals that help inhibit the growth of micro-organisms. Meat is often also cured with salt or sugar, or a combination of the two.

Curing draws moisture from the meat through a process of osmosis. Nitrates and nitrites are also often used to cure meat.

Pickling is a method of preserving food by placing it in either a brine (high in salt), or a solution of vinegar which is too acidic to permit bacterial growth.

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.

A 1950s issue of Popular Mechanics details the impending arrival of "food irradiation". However, at the present time, the implications surrounding the irradiation of food are still not fully understood, and the technology is therefore still not in widespread use. However, irradiation of potatoes, strawberries, and meat is common in many countries where refrigerated facilities and trucks are not common. In 2002, the FDA permitted irradiation of meat and poultry to reduce the spread of E. coli and Salmonella. In the US and most of Europe irradiation of spices is common, as the only alternative (treatment with gas) has been shown to be potentially carcinogenic. The process is incorrectly called "pasteurization" to avoid the reduced sales that arise from the correct term of "irradiation".