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This spring, the University of Wisconsin-Madison published research showing that atmospheric steam canners may be used to safely can naturally acidic foods such as peaches, pears, and apples, or acidified foods such as salsa or pickles.
But certain criteria must be met for the food to be safe to eat when using these canners, says Barbara Ingham, food science specialist with the University of Wisconsin-Extension.
“Foods must be high in acid, with a pH of 4.6 or below,” says Ingham. “Either a boiling water canner or an atmospheric steam canner can be used to safely preserve foods that are high in acid.”
Ingham offers the following important food safety guidelines for using an atmospheric steam canner.
• Start with a research-tested recipe developed for a boiling water canner. You can find approved recipes in UW-Extension publications available at fyi.uwex.edu/safepreserving/, or from the National Center for Home Food Processing and Preservation at nchfp.uga.edu. Follow the directions in the research-tested recipe, simply using a steam canner rather than a boiling water canner for processing. Do not rely on the booklet that accompanies the canner to provide safe canning instructions.
• Jars must be processed in pure steam at 212°F. Vent the canner prior to starting the processing time until a full column of steam appears. A 6- to 8-inch column of steam should be venting from the hole(s) in the side of the canner during the entire timed process. Ideally, temperature should be monitored with a thermometer placed in the vent port, but the placement of jars in the canner may make this difficult. Some appliances come with a built-in temperature sensor in the dome lid and these appear to be accurate.
• Jars must be heated before they are filled with hot liquid (raw or hot pack), just like you normally would for a boiling water canner. Minimize cooling prior to processing. An atmospheric steam canner may be used with recipes approved for half-pint, pint or quart jars.
• Modify the processing time for elevations over 1,000 feet. Roughly 40% of Wisconsin is higher than 1,000 feet. Adjust the processing time as outlined in a recipe tested for a boiling water canner. The elevation for any address can be checked here: http://www.daftlogic.com/sandbox-google-maps-find-altitude.htm
• To avoid the canner boiling dry, limit processing time to 45 minutes or less, including any modification for elevation. When processing food, the canner should not be opened to add water. Regulate heat so that the canner maintains a temperature of 212°F. A canner that is boiling too vigorously can boil dry within 20 minutes. If a canner boils dry, the food is considered under-processed and therefore potentially unsafe.
• Cool jars in still, ambient air. Cooling is important for safety. Jars should be cooled on a rack or towel away from drafts. Do not place them in the refrigerator to hasten the cooling process.
To learn more, contact the St. Croix County UW-Extension office at 715-651-1930.