University of Wisconsin - Extension

Summer finds some pantry shelves stocked with row upon row of home-canned food. Foods that are naturally low in acid, such as meat and vegetables, must be pressure canned to ensure safety. Perhaps the pressure canner that you use was handed down to you from your mother or grandmother, or maybe your pressure canner is brand new. Regardless, pressure canners are often confused with pressure cookers, and it is important to understand the difference, according to Barb Ingham, University of Wisconsin-Madison/Extension food science specialist.

Both pressure canners and pressure cookers work by trapping steam and building up pressure inside a pot. The steam is trapped because the lid, which is fitted with a rubber gasket, forms an airtight seal once it's locked into position. As the contents of the pot heat up, steam gets trapped and pressure builds. At 15 pounds pressure, water boils at 250°F, almost 40°F higher than in conventional pots. The high pressure and temperature destroy microorganisms more rapidly (pressure canning) or cook foods more quickly (pressure cooking).

Pressure canners are used for canning low-acid foods such as meat and vegetables. The high temperatures created in a pressure canner (240°F-250°F) are necessary to destroy spores of the bacterium Clostridium botulinum.

"If the spores of C. botulinum are not destroyed," Ingham says, "they can produce a deadly toxin in any low-acid home canned food."

There are two styles of pressure canners, those with a dial gauge and those with a weighted gauge. Be sure to carefully follow the manufacturer's directions for the type of canner that you have. And remember that a dial gauge canner must be tested annually to ensure that the gauge is reading accurately. Weighted gauge canners do not need to be tested, but it is still a good idea to carefully inspect the canner, and replace worn parts as necessary.

Pressure cookers or pressure saucepans are used to rapidly cook meats, sauces, vegetables and other foods for a family meal. Because they heat food rapidly, and help to tenderize tough cuts of meat, pressure cookers are a fixture of many households. However, it is important to remember that pressure cookers cannot be used to safely pressure can foods because they do not maintain adequate pressure, and they heat and cool too rapidly to ensure a thorough process.

Pressure canners and pressure saucepans come in a wide variety of sizes. Pressure canners may hold up to 22 quarts of canned food, and are able to process food at pressures up to 25 pounds. Some popular brands of pressure canners are Mirro, Presto and All American. Pressure cookers usually hold no more than 6 quarts, and they often cook food at 'high', 'medium' or 'low' settings. While some pressure canners are able to double as pressure cookers, pots sold as pressure cookers cannot be used to can foods.

Both pressure canners and pressure cookers that you'll find in the stores today are a far cry from their predecessors. The new 'second generation' pots are lighter in weight, and they have new built-in safety features that release steam if the pressure gets too high -- features that make them more fun and easy to use. If you are careful to follow the directions that accompany your pressure canner or cooker, you will enjoy using these contemporary pots. For safe home canning recipes using a pressure canner, contact your county UW-Extension office.

UW-Extension has a publication series available on preserving foods from the garden. The Wisconsin Safe Food Preservation Series by Barbara Ingham includes the revised Canning Fruits Safely (B0430), Making Jams, Jellies and Preserves (B2909), Freezing Fruits and Vegetables (B3278), Canning Vegetables Safely (B1159), Canning Salsa Safely (B3570), Tomatoes Tart and Tasty (B2605), Homemade Pickles and Relishes (B2267) and Canning Meat, Wild Game, Poultry and Fish Safely (B3345).

These and other gardening and food preservation publications are available from your county UW-Extension office or from Cooperative Extension Publications (877-947-7827) and online at http://www1.uwex.edu/ces/pubs .

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File: Food safety