Organisms that cause food spoilage–moulds, yeasts and bacteria–are present everywhere in the air, soil and water. Enzymes that may cause undesirable changes in flavour, colour and texture are present in raw vegetables.
When vegetables are canned, they are heated hot enough and long enough to destroy spoilage organisms. This heating (or processing) also stops the action of enzymes.
Pressure canning is the only safe method of canning all vegetables (except tomatoes). Jars of food are placed in a pressure canner which is heated to a temperature of at least 240°F (116°C). This temperature can be reached only in a pressure canner.
Pressure Canning Meats