Canning is a food preservation method that seals food in airtight containers and applies heat to destroy microorganisms that cause spoilage. The heat processing destroys pathogens, including Clostridium botulinum spores, and creates a vacuum seal that prevents recontamination. Canning is the most widely recommended method for preserving low-acid vegetables, meats, and seafood at home.
The canning process was developed by Nicolas Appert in 1809 in response to a French government prize for a method of preserving food for military use. Appert's method used glass jars sealed with cork and wax. In 1810, Peter Durand patented the use of tin-plated steel cans. The home pressure canner was developed in the early 20th century, and the USDA published its first comprehensive canning guide in 1917. Modern canning methods are based on scientific research conducted at the National Center for Home food Preservation.
The safety of canned food depends on the heat treatment. Low-acid foods (pH above 4.6) require Pressure Canning at 115 to 121 degrees Celsius (240 to 250 degrees Fahrenheit) to destroy Clostridium botulinum spores. High-acid foods (pH below 4.6) can be safely processed in a boiling water bath at 100 degrees Celsius (212 degrees Fahrenheit). The processing time depends on the food type, jar size, and altitude. Altitude adjustments are required above 300 meters (1,000 feet).
The basic canning equipment includes jars with two-piece lids (screw band and flat lid), a jar lifter, a canning funnel, a bubble remover, and a lid magnet. A water bath canner is a large pot with a rack that holds jars off the bottom. A pressure canner is a heavy pot with a locking lid, pressure gauge, and safety valve. Dial gauge pressure canners are tested annually for accuracy.