Home canning tip -- heat processing.
Heat processing -- heating filled jars of food to a specified temperature for a specified time -- is essential for the food safety of all home canned foods.
Processing destroys micro-organisms that enter the jar upon filling. These micro-organisms can cause food spoilage during storage at room temperature. Processing also exhausts air from the jars so that when they cool and the food inside contracts, a strong vacuum will be created inside the jar. This vacuum sucks the lid down onto the mouth of the jar, creating an airtight seal.
High acid foods, like jams, jellies, fruits, tomatoes and pickles, may be safely processed in a boiling water canner. A large pot, with a close-fitting lid and rack to lift jars off the bottom, may be used if a boiling water canner is unavailable. Just be sure the pot is deep enough to allow jars to be covered with at least 2.5 cm of water, and provides room for a full, rolling boil.
Low acid foods, like vegetables, meats, seafoods, and tomatoes combined with other vegetables, must be processed at a temperature of at least 240F (116C) to eliminate the risk of botulism. The only way to achieve this temperature is in a pressure canner.