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University of Illinois Extension

Boiling Water Bath Canning versus Pressure Canning

Before doing any canning, it’s essential that you understand the difference between the two methods of canning and that you use the correct method for the product you are preserving. The two methods include boiling water bath canning and pressure canning. Knowing which one to use, and how to use it correctly, will protect the health and safety of those consuming the product. NOTE: if a pressure canner is used in a cottage food operation, it must only be for properly acidified and permitted foods, NOT for low-acid foods.

Boiling water bath canning

Heat is transferred to the food by the boiling water that surrounds the jars. This boiling temperature of 212°F for the time specified in an approved recipe is sufficient to destroy molds, yeasts, enzymes, and some bacteria. Processing times are usually given for altitudes under 1,000 feet above sea level. Illinois' mean elevation is 600 feet above sea level with the highest point of elevation (1,235 feet) at Charles Mound in northern Jo Daviess County. At higher altitudes, water boils at lower temperatures, making it necessary to process foods longer.

What type of foods can be processed in a boiling water bath canner?

Generally, high-acid foods or acidified foods can be safely canned in a boiling water bath canner.

  • Fruits
  • Jams, jellies, preserves, conserves, and marmalades
  • Tomatoes, tomato sauces without meat, tomato juice and salsa. However, they are borderline between high and low acid and need acid added to them (commercial lemon juice or vinegar). All canned tomato recipes must be from an approved recipe (USDA or state cooperative extension service) and followed exactly, or you must submit a recipe to a commercial laboratory to be tested
  • Fermented foods, such as crock/fermented pickles, kimchi, and home canned sauerkraut. It is highly recommended that cottage food producers send their acidified and fermented vegetable recipe samples to a lab for testing.
  • Foods to which a sufficient amount of vinegar is added, such as pickles and pickled products

Pressure canning

The bacterium of greatest concern in home canning is Clostridium Botulinum because it can produce spores that generate a dangerous and potentially deadly toxin that causes food poisoning. Botulism spores thrive on low-acid foods in the absence of air, in the presence of moisture, and at room temperature, which are the conditions inside a jar of home-canned meat or vegetables. Spores of Clostridium Botulinum may survive at boiling water bath temperatures, but they are destroyed when processed in a pressure canner where the temperature reaches 240°F or higher. Where altitudes are 1,000 feet or lower, such as in Illinois, all low-acid foods must be processed in a pressure canner operated at 10 PSIG for weighted gauge pressure canners and 11 PSIG for dial gauge pressure canners for a designated amount of time. PSIG is pounds per square inch of pressure as measured by a gauge. At temperatures of 240° to 250°F, the time needed to destroy bacteria in low-acid canned food ranges from 20 to 100 minutes, as stated in a tested recipe. This time and pressure cannot be altered.

A pressure cooker cannot be used as a pressure canner. (Read the National Center for Home Food Preservation for more information).

Pressure canner dial gauges should be tested for accuracy each year. Contact your local University of Illinois Extension office to determine locations and times for testing. There is usually no charge for testing dial gauges, and it only takes a few minutes.

What type of foods can be processed in a pressure canner?

Low-acid food require processing in a pressure canner. NOTE: These are NOT allowed in a cottage food operation.

  • Meats, including beef, pork, poultry, fish, seafood and wild game
  • Vegetables, other than acidified tomatoes/tomato products, and properly fermented products...pickles/pickled products
  • Soups and stews
  • Meat sauces
  • Other combination foods