Dilly Beans - Pickled Green Beans

Category: File - :Appert Nicolas.jpg|thumb|250px|Nicolas Appert, developer of the canning process.

Category: File - :Berthold Weiss Canned Foods.jpg|thumb|250px|One of the first large canned food factories, of the Weiss brothers in Csepel-Budapest. A trade card from 1885

Category: File - :Canned food factory (1898).jpg|thumb|250px|How tinned food was made, a picture from Albert Seigneurie's Grocery Encyclopedia (1898)

Canning is a method of preserving food in which the food is processed and sealed in an airtight container. The process was first developed as a French military discovery by Nicolas Appert. The packaging prevents microorganisms from entering and proliferating inside.

To prevent the food from being spoiled before and during containment, quite a number of methods are used: pasteurization, boiling (and other applications of high temperature over a period of time), refrigeration, freezing, drying, vacuum treatment, antimicrobial agents that are natural to the recipe of the foodstuff being preserved, a sufficient dose of ionizing radiation, submersion in a strongly saline, acid, base, osmotically extreme (for example very sugary) or other microbe-challenging environments.

No such method is perfectly dependable as a preservative. For example, spore forming thermal resistant microorganisms, such as Clostridium botulinum (which causes botulism) can still survive.

From a public safety point of view, foods with low acidity (a pH more than 4.6) need sterilization under high temperature (116-130°C). To achieve temperatures above the boiling point requires the use of a pressure canner. Foods that must be pressure canned include most vegetables, meats, seafood, poultry, and dairy products. The only foods that may be safely canned in an ordinary boiling water bath are highly acidic ones with a pH below 4.6http://www.extension.umn.edu/distribution/nutrition/DJ1097.html, such as fruits, pickled vegetables, or other foods to which acidic additives have been added.