Preservation

• Canning preserves food in two ways. During the canning process, heat kills off microorganisms in the food. The heat also drives air out of the jar, expelling any microorganisms in the air and creating a vacuum seal that keeps germs out. Without exposure to air, the food inside the jar won't spoil for up to a year. There are two types of canning: water bath canning and pressure canning. Different foods may need different types of canning.
  
  

Pressure Canning

• Pressure canning uses a special type of pressure cooker to heat jars to 240 degrees F or above. This high heat is necessary to destroy Clostridium botulinum spores, the microorganism that causes the dangerous condition botulism. Most types of food need to be canned in a pressure canner, such as meats and vegetables, as these foods don't contain enough acid to naturally kill off Clostridium botulinum spores.
  
  

Water Bath Canning

• Some food contains enough acid to be naturally free of Clostridium botulinum spores. Jellies, jams, pickles, and other preserves usually are high in acid content, as are fruits and tomatoes. These foods can be canned using a water bath, during which jars are immersed in boiling (212 degrees F) water. The water kills off the microorganisms and forms a vacuum seal. Water bath canning is easier than pressure canning as a special machine isn't necessary.