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Atmospheric Steam Canners for Home Food Preservation

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.

Atmospheric steam canners may be used for home canning of naturally acid foods such as peaches, pears, and apples, or acidified-foods such as salsa or pickles, as long as all the following criteria are met:

  • Foods must be high in acid, with a pH of 4.6 or below. Either a boiling water canner or an atmospheric steam canner can be used to safely preserve foods high in acid.
  • A research tested recipe developed for a boiling water canner must be used in conjunction with the steam canner. Approved recipes are available from sources such as the National Center for Home Food Processing and Preservation at http://nchfp.uga.edu/ The booklet accompanying an atmospheric steam canner can’t be relied on to provide safe canning instructions. Consumers follow a tested recipe, simply using a steam canner, instead of a boiling water canner, at the processing step.
  • Standard canning jars with 2-piece metal lids must be used.
  • Jars must be processed in pure steam at 210-212°F. Temperature should be monitored with a thermometer placed in the vent port. Steam has to flow freely from the canner vent(s) during the entire process, or the food is considered under-processed/unsafe. Some of atmospheric steam canners come with a built-in temperature sensor in the dome lid that, in lab testing, appears to be accurate.
  • Jars must be heated prior to filling, and filled with hot liquid (raw or hot pack). Tested recipes that allow half-pint, pint, or quart jars may be followed.
  • Processing time must be modified for elevation as required by a tested recipe.
  • Processing time must be limited to 45 minutes or less, including any modification for elevation. The processing time is limited by the amount of water in the canner base. When processing food, the canner should not be opened to add water. Regulate heat so that the canner maintains a temperature of 210-212°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.
  • Cooling of jars must occur in still, ambient air. Cooling is important or safety. Jars should be cooled on a rack or towel away from drafts. Jars should not be force-cooled.

References:

 

Information provided by Barbara Brown, Food Specialist, Oklahoma Cooperative
Extension Service                                                                               3/18

 

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