Home food preservers are always looking for ways to make their job easier, simpler, and to relieve the hot temperatures of the kitchen in the summer. Researchers Dr. Elizabeth Andress, of the National Center for Home Food Preservation, and Drs. Paola Willmore, Mark Etzel and Barbara Ingham of the University of Wisconsin-Madison have published their findings on the atmospheric steam canner versus the boiling water bath canner technique. The food products used in the testing of the atmospheric steam canner were apple sauce, chocolate raspberry sauce, cranberries in heavy syrup, and tomato juice. The researchers used standardized half-pint glass jars, pint glass jars, and quart size glass jars. The researchers have made the following recommendations for home preservers, who choose to use an atmospheric steam canner:

1. The food product to be canned must have a pH level less than or equal to 4.6 meaning the product must be high in acid content.
2.  A research-tested recipe must be used with the atmospheric steam canner. The home preserver cannot use just any recipe. Michigan State University Extension recommends using research-tested recipes. United States Department of Agriculture Complete Guide to Home Canning or the National Center for Home Food Processing and Preservation are two resources that are available for research-tested recipes. The researchers do not consider the instruction booklet that comes with the atmospheric steam canner to research-tested.          
3. The temperature of the steam inside the atmospheric steam canner must be monitored to make sure that it reaches the 212 degrees Fahrenheit. When the temperature of boiling water(212°F.) is reached inside the atmospheric steam canner, the venting process is complete and all of the air has been purged from the canner. It is at this point that the process of heat transfer to the food product is at its highest value. The consumer needs to use either a bimetallic stem thermometer or a digital thermometer put in the vent port of the atmospheric steam canner to monitor the temperature.
4. The jars must be hot when filled with hot food to be processed in the atmospheric steam canner. The hot jars filled with hot food will begin to cool if not placed immediately in a preheated atmospheric steam canner or boiling water technique canner. The time the jars are cooling must minimize as much as possible.
5. Recipes must be adjusted for altitudes above 1,000 feet above sea level. Use a research-tested recipe for the boiling water bath technique to make the adjustments for the altitude changes for the atmospheric steam canner.
6. The processing time for the food product to be canned in the atmospheric steam canner must be less than 45 minutes or there is the risk that the canner will run dry of water. Consumers must avoid opening the atmospheric steam canner to add water during processing because to do will cause a drop in temperature, resulting in the food being underprocessed and potentially being unsafe to eat.
7. The cooling of the canned food product should be done at room temperature. During this cooling process, most of the killing of the food borne illness bacteria takes place. Therefore, there should be no shortcuts to the cooling process.

It is vital that consumers follow these critical processing recommendations when they use the atmospheric steam canner to process food for their families.

Reference:

Willmore, Paola, Etzel, Mark, Andress, Elizabeth, Ingham, “Home Processing of Acid Foods in Atmospheric Steam and Boiling Water Canners,” Food Protection Trends, Vol.35. No. 3, p.150-160