Canning With a Pressure Canner
Low acid foods, such as, carrots, green beans, and corn must be processed in a steam pressure canner. A steam pressure canner is a heavy kettle (pot) with a lid which can be clamped down or locked down to make a steam-tight seal. The lid is fitted with a safety value, a petcock (steam vent) and a pressure gauge or regulator. Two types of steam pressure canners are available at stores; those with dial gauges and those with weighted gauges.
In order to destroy all bacteria, their spores and the toxins they produce, low acid foods must be superheated to a temperature of 240 degrees Fahrenheit and held there for the time specified by the recipe. Because the steam inside the canner is pressurized, its temperature exceeds the boiling point of water.