How does the home-canning of food work and what is the effect for shelf life?

Germany

Canning is good method of food preservation if practiced properly. The canning process consists of placing foods in jars and heating them to a temperature that destroys viruses, bacteria, yeast and moulds, that could be a health hazard or cause the food to spoil.

The reduced numbers of microorganisms, and also the fact, that canned food don’t come in contact with oxygen or light (as long as it is not canned in glass containers) extend the shelf life 3-5 times versus conventional storage methods (time depending on the food, the packaging material and the heat treatment applied). There are two important differences in canning, based on the acidity of the product.

• Low pH foods like fruits, tomatoes, pickles as well as jam and jellies (pH of 4.6 or lower) can be safely canned at boiling temperatures (e.g. boiling water bath at about 75°-100°C)
• High pH foods like meat and vegetables (pH of higher than 4.6) need undergo a canning in a pressure cooker to get a temperature of 115 °C or above in order to kill the thermo-resistant bacterial spores.