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It’s not your Grandma’s canning


Linda Geist
University of Missouri Extension
Phone: 573-882-9185

Published: Friday, Aug. 9, 2013

Story source:

Vera L. Massey, 573-445-9792

COLUMBIA, Mo. – The joy of canning fresh fruits and vegetables is the same as when Grandma ‘put up’ the season’s bounty. But some home canning methods have been improved over the years to reduce the risk of botulism, says an MU Extension nutrition and health education specialist.

Vera Massey of the Boone County Extension office is seeing an increasing number of people who are canning for the first time or returning to it after many years away.

What was good enough for Grandma may not be good enough today, she says.

“That doesn’t mean everything Grandma did is wrong,” she says, “but there are safer ways to do things based upon scientific research.”

USDA guidelines have been revised over the past 20 years. If you follow these simple guidelines, Massey said, you can avoid botulism.

She likens it to having surgery. “If I’m going in for surgery, I don’t want the techniques they used 30 years ago I want the techniques that will reduce risk. It’s the same when we can foods,” she says.

Canning tomatoes is different than it was years ago because most of today’s varieties of tomatoes are low-acid. Tomatoes must contain sufficient acid to can safely, and bottled (not fresh) lemon juice or citric acid must be added to produce sufficient acid levels, whether you are using a boiling water canner or pressure canner.  

All jellied products must be processed in a boiling water canner to prevent mold growth. Don’t use paraffin to seal jars of jellies or jams, she says. When the wax topper is used, toxic yeast or molds can grow.  If mold is present on jellies or jams, do not scrape the mold away. Discard the entire contents to prevent poisoning.

Massey also cautions canners against using Internet advice unless it is from USDA or university extension sources. One of her favorite resources for safe methods and tested recipes is the National Center for Home Food Preservation, University of Georgia, at

One of the most popular Internet-suggested methods is oven canning. This is not safe because ovens don’t provide sufficient heating to destroy harmful bacteria and produce a proper seal. There is also a risk of jars exploding. 

“Canning is not cooking,” Massey reminds students in a six-week food preservation series offered annually by nutrition specialists across the state. “Canning is a science. As long as you use recommended guidelines, you will reduce your risk of botulism.”

One thing that has not changed is the availability of pressure canner dial gauge checks at the local extension office.

Dial gauges should be checked annually for accuracy before use. Check with your local MU Extension office for information on this service.

Numerous low-cost or free guidesheets are available for download on the MU Extension website. A free self-study course is available at