General Canning Information
Equipment and Methods Not Recommended
Open-kettle canning and the processing of freshly filled jars in conventional ovens, microwave ovens, and dishwashers are not recommended, because these practices do not prevent all risks of spoilage. Steam canners are not recommended because processing times for use with current models have not been adequately researched. Because steam canners do not heat foods in the same manner as boiling-water canners, their use with boiling-water process times may result in spoilage. It is not recommended that pressure processes in excess of 15 PSI be applied when using new pressure canning equipment. So-called canning powders are useless as preservatives and do not replace the need for proper heat processing. Jars with wire bails and glass caps make attractive antiques or storage containers for dry food ingredients but are not recommended for use in canning. One-piece zinc porcelain-lined caps are also no longer recommended. The older glass and zinc caps used flat rubber rings for sealing jars, but too often fail to seal properly.
Note: The above language is in the 2009 USDA Complete Guide to Home Canning. Subsequent research has provided information on methods that can be applied to successfully use atmospheric steam canners for home canning of naturally acid and properly acidified foods. Please read this page for more information.
This document was adapted from the "Complete Guide to Home Canning," Agriculture Information Bulletin No. 539, USDA (Revised 2009). The Note was posted as an addendum on 9/14/2015.
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