Canning involves placing foods in jars or similar containers and heating them to a temperature that destroys harmful spoil-causing micro-organisms. During the heating process, air is driven out of the jar and as it cools, a vacuum seal is formed. This vacuum seal prevents air from getting back into the product and bringing with it contaminating micro-organisms. There are two types of canning, which use different types of canners:
Boiling Water Canning
Boiling water canning is used for high acid foods, such as fruits and fruit juices, tomatoes and tomato sauces, jams and jellies. Boiling water canning utilizes aluminum or porcelain-covered steel pots with removable perforated racks and fitted lids. The canner must be deep enough to allow for one inch of briskly boiling water to cover the tops of jars during processing.
Pressure canning is used for low acid foods, such as vegetables, meats and poultry. Modern pressure canners are lightweight, thin-walled kettles typically having turn-on lids. They include a jar rack, gasket, dial or weighted gauge, automatic vent/cover lock, vent port or steam vent with a counterweight or weighted gauge and a safety fuse.