Steam canning can be just as safe as water bath canning if performed properly to preserve acidic foods. Here are guidelines for operating a steam canner.
Last year, I used a steam canner for preserving produce. I’ve heard that the U.S. Department of Agriculture doesn’t consider steam canners safe, however — is that true?
An atmospheric steam canner is a two-part pot with an inner rack for holding jars and a tall cover that allows a steady stream of steam to flow around the jars. It requires only about 2 quarts of water to process seven 1-quart jars of high-acid foods, whereas a water bath canner requires about 2-1/2 gallons of boiling water to do the same job. A steam canner saves significant time and energy, doesn’t emit as much heat, and requires less heavy lifting compared with using a water bath canner.
For more than a decade, information on the safety of steam canning has remained incomplete. But researchers from the University of Wisconsin, Madison, funded by a grant from the USDA and the National Center for Home Food Preservation (NCHFP), have now concluded that steam canners can be as safe and effective as water bath canners when properly used to preserve acidified or naturally acidic foods. They released the following guidelines for safely operating a steam canner for home food preservation:
- Only steam can foods high in acid, with a pH of 4.6 or below.
- Always use a research-tested recipe developed for a water bath canner. Acquire recipes from university extension programs or from the NCHFP. The booklets that accompany steam canners usually don’t provide safe instructions.
- Heat jars prior to filling them with food, and minimize the amount of cooling time that passes prior to processing. You can use half-pint, pint, or quart jars.
- Process jars only after the temperature reaches pure steam at 212 degrees Fahrenheit. Wait to start the processing time until the canner has vented and a full, steady column of steam appears. Monitor the temperature with a thermometer.
- Modify processing time for elevation — in general, add 5 minutes for each 1,000 feet you’re above sea level in elevation.
- Only use recipes that require 45 minutes of processing time or less, as the amount of water in the canner may not last any longer. Don’t open the canner to refill the water while processing foods.
- Cool the jars in still, ambient air. Cool jars on a rack or towel away from drafts. Don’t place them in the refrigerator to hasten the process.
Steam canners usually have ribbed bottoms, so they shouldn’t be used on glass-topped stoves. Also, don’t use steam canners in place of pressure canners, which seal in pressurized steam to achieve the high temperatures needed to safely can low-acid vegetables and meats.
Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website.