Canning Controversy: What About Steam Canners?

Clemson Extension, the National Center for Home Food Preservation at the University of Georgia, multiple other University Extension Services and the United States Department of Agriculture recommend that steam canners not be used. This recommendation is based on the lack of sufficient research to determine safe processing times for use with current steam canner models.

Information available on steam canners to date is contradictory. In the mid 1980’s Dr. Von Mendenhall at Utah State University did some research for a Salt Lake City steam canner manufacturer. In a personal letter (1986), he wrote that, based on research at Utah State and the University of Massachusetts, steam canning is safe for high acid foods only (fruits, jams and jellies). However, there is no indication that his work was published or that it was reviewed by his peers. Pennsylvania State University’s Dr. Gerald D. Kuhn, who compiled the first edition of the USDA Complete Guide to Home Canning, disagreed and did not recommend the use of home canners.  In March 2005 Dr. George York (University of California-Davis) published a research article in Food Protection Trends entitled, “Home Processing of Tomatoes and Other Acid Foods in Flowing Steam and Hot Water Bath Canners” (by M. Samida, L. Geer, and G. K. York). The authors wanted to determine whether steam canners could be as safe as hot (boiling) water bath canners for home canning of acid foods. They processed four foods – tomato juice, peaches, whole peeled tomatoes and applesauce. First, they measured the time for the water or steam to reach a temperature of 212°F for both types of canners; then, they compared the time to reach the target temperature (180°F) at the center of the product. The products in each type canner required the same or nearly the same time to reach the target temperature. The authors concluded that USDA recommended processing times are adequate for acid foods and that the two types of canners are equally safe to use. Unfortunately, no study confirming their results has been published to date. Dr. Barbara H. Ingham and Paola Flores at the University of Wisconsin-Madison are investigating the efficacy of steam canners. Through their work, they hope to resolve issues surrounding steam canners by developing safe steam canning processes and writing a consumer guide to steam canning. They anticipate publishing by the end of 2014.

Again, due to the lack of definitive research into the safety of steam canning, Clemson Extension program currently agrees with the present USDA and National Center for Home Food Preservation recommendation against using Steam Canners. Utah State University also agrees with this position.

For those consumers who still wish to use steam canners, regardless of recommendations to the contrary, we very strongly advise against steam canning any low acid foods (e.g. vegetables, meat, poultry, fish) or any borderline acid foods (e.g. tomatoes, figs). Steam canning these foods causes underprocessing and is not sufficient to kill spores of Clostridium botulinum. Underprocessing low acid and borderline acid foods can lead to botulism food poisoning.

Those consumers who still wish to use steam canners for processing acid foods (fruits, jams or jellies) should at minimum follow Dr. Mendenhall’s six suggested steps to increase successful operation of a steam canner:

  1. Place appropriate amount of water in the base. Place the perforated cover over the base and bring water to a low boil.
  2. Pack and fill jars. Secure lids firmly, but not over-tight. Set each full jar on the base and allow it to warm up while packing and filling enough jars for one batch.
  3. When the last full jar has warmed up for 1-2 minutes, place the dome on the base and slowly (4-5 minutes) increase temperature setting of the stove until a column of steam 8-10 inches is evident from the small holes at the base of the dome.
  4. Begin timing the process, maintaining the column of steam following the water bath canning recommendations adjusted for your altitude. Do not reduce temperature setting of the stove. The dome should not bounce from the base during processing.
  5. When processing time is complete, turn off the stove and wait 2-3 minutes before removing the dome. Remove the dome by turning it away from your face and body to avoid burns.
  6. Allow jars to cool and seal. Remove metal bands and store the jars in a cool dark place.

Please remember that no recommended steam canner processes for foods are currently available. This Tip will be updated as soon as new science-based recommendations are released.

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