Burning Issue: Using Atmospheric Steam Canners
Can acid foods be processed in steam canners?
The University of Wisconsin, under the leadership of Dr. Barbara Ingham, has conducted research on appropriate use of atmospheric steam canners for home canning in collaboration with the National Center for Home Food Preservation (NCHFP). Atmospheric steam canners are used for processing naturally acid or properly acidified foods with natural or equilibrated pH values of 4.6 or below. They are not pressurized vessels used for processing for low-acid foods.
Sufficient studies and peer review have been completed that we are now able to say that as long as certain critical controls at various steps in the canning process are achieved, USDA and NCHFP process times for canning acid or properly acidified foods (pH of 4.6 or below) at home with properly research based recipes and procedures can be used. The research looked at temperature distribution in the steam environment surrounding the jars in a dome-style steam canner, heating patterns of several different food types during processing in the canner, and the contribution of standardized cooling procedures at the end of the process time.
Some of the key controls in addition to the acidity of the food product are knowing that the canner has had the air vented out of the steam before processing begins, and that the pure steam is at the temperature of boiling water at the start and during processing. Jars must be preheated before filling with food and cooling prior to processing must be minimized. Processing times must be adjusted for altitude, and must also be 45 minutes or less, including any altitude modification. The processing time is limited by the amount of water the canner base will hold, and the canner cannot be opened to add water or for any reason at any time during the process. Finally, cooling of jars must take place in still, ambient air without any forced, more rapid cooling. The slow cooling of processed jars is important to the overall food safety of the whole canning procedure.
Dr. Ingham provides further instructions and details about carrying out canning in an atmospheric steam canner using USDA acid food processing recommendations at her webpage: http://fyi.uwex.edu/safepreserving/2015/06/24/safe-preserving-using-an-atmospheric-steam-canner/ .
Eventually we will integrate this more complete advice into additional offerings on the National Center for Home Food Preservation website.
The results of this research were published in a peer-reviewed scientific journal in May 2015.
Willmore, P, Etzel, M, Andress, E. and Ingham, B. (2015). Home processing of acid foods in atmospheric steam and boiling water canners. Food Protection Trends, Vol 35, No. 3 (May-June), p.150–160.
September 9, 2015
National Center for Home Food Preservation
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