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Atmospheric Steam Canners Can Provide a Safe Alternative to Boiling Water Canning for Acid Foods

carolina canning

Carolina Canning

We’ve heard many questions throughout the 2015 canning season. Some we frequently hear are “What about steam canners? Are they safe? Can I use them with a recommended boiling water process?” Due to the lack of definitive scientific research, we previously have not recommended using steam canners (see Tip #42, April 14, 2014). However, a recent peer-reviewed scientific paper by Willimore, Etzel, Andress and Ingham (May-June 2015 issue; Food Protection Trends vol. 35, no. 3, p. 150-160) investigates atmospheric steam canner processing and describes conditions for using it safely. This Tip summarizes the recommendations from that paper.

Precautions for Safely Using Atmospheric Steam Canners for Processing Acid Foods:

Willimore, Etzel, Andress and Ingham (2015) compared the heat treatment achieved with a boiling water canner and an atmospheric steam canner for various acid foods. Using recommended boiling water processes, they processed applesauce, tomato juice, cranberries and chocolate raspberry sauce in both types of canners. Their results established the effectiveness of the atmospheric steam canner for home processing foods that have a pH equal to or less than 4.6. Observing the following precautions allows for safe processing of food in an atmospheric steam canner at home.

  • Process only food products that are high in acid in an atmospheric steam canner; the food pH must be less than, or equal to pH 4.6. If a tested recipe is used, either a boiling water canner or an atmospheric steam canner can be used to safely preserve high acid foods.

Do not process low acid foods in an atmospheric steam canner; a science-based, research-tested pressure canner process is required to ensure the safety of low acid canned foods such as vegetables, meat, poultry and fish.

  • Use a current, research-tested recipe developed for boiling water canners with atmospheric steam canners. Approved recipes may be found in the USDA Complete Guide to Home Canning, at the National Center for Home Food Processing and Preservation (nchfp.uga.edu) or the Clemson Home and Garden Information Center (hgic.clemson.edu) but not in atmospheric steam canner instruction booklets.

  • Monitor temperature in the atmospheric steam canner to make sure that the process time begins only when the temperature of pure steam is reached (212°F at 0 to 1000 feet). When the steam temperature in the canner dome reaches the boiling point (~212°F), venting is complete, all air is purged from the canner, and heat is transferred most efficiently. Monitor temperature with a calibrated dial-stem or digital thermometer placed in the vent port. Steam vent size or intensity does not accurately indicate the steam temperature. Some atmospheric steam canners are equipped with a built-in temperature sensor in the dome lid and these appear to be accurate.

  • Heat jars prior to filling. Keep jars hot prior to the start of the processing time. Recognize that jars will cool if placed in canners that have not been preheated. To minimize cooling of jars, preheat both atmospheric steam canners and boiling water canners before adding hot jars filled with food.

  • The authors’ research indicates that other operating parameters for an atmospheric steam canner are more flexible: as long as research-tested methods are followed, the canner may be operated full or nearly empty; current, research-tested recipes may be followed for half-pint, pint, and quart-size jars; hot-packed or raw-packed foods may be safely canned by approved recipes.

  • Make altitude adjustments. For elevations above 1,000 feet, the processing times recommended in research-tested recipes for boiling water canners should be followed.

  • Limit processing time to 45 min or less. To prevent the canner boiling dry, only foods with a research-tested process time of less than 45 min should be canned in an atmospheric steam canner. Consumers must not open the canner to add water during the process; doing so will lower the temperature and may result in underprocessed, unsafe food.

  • Cool jars in still, ambient (room) temperature air. Most microbial kill occurs during air cooling; thus the cooling procedure is extremely important. Do not cool jars in water, in the refrigerator, in front of a fan or by hastening the cooling process in any other way.

Consumers who observe these precautions can be assured that they are preparing safe food for their families through use of an atmospheric steam canner.

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