Shannon Carter, left, demonstrates proper use of a pressure canner during one of 10 home food preservation classes she offered this summer. (photo: Ken Chamberlain, CFAES)

OSU Extension Provides Home Food Preservation Tips

It was from potato salad, made with improperly home-canned potatoes.

Foodborne botulism is rare, but the April 2015 incident was a somber reminder of the importance of strictly following home food preservation guidelines, said Shannon Carter, family and consumer sciences educator in Fairfield County for Ohio State University Extension. OSU Extension is the outreach arm of The Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

Last year, Carter offered two home-food preservation classes to county residents. This year, she offered 10. And those were just a few of the classes offered by OSU Extension across the state. See the upcoming class list, along with links to how-to videos and other resources.

“Foodborne botulism can be caused by using the wrong canning method,” Carter said. A pressure canner, rather than a simple boiling water bath, is necessary to kill botulism spores in low-acid canned foods such as meat, potatoes and other vegetables.

“But people still water-bath their green beans and other foods,” Carter said. “And if they’ve done it that way successfully for years, why would they change?”

Even if canning jars are properly sealed, botulism spores can grow. In fact, such spores can grow only in a sealed environment without oxygen, Carter said, along with high-moisture and low-acid conditions.

“Water boils at 212 degrees,” she said. “If you have a boiling water canner, you can boil something for three, five, even 25 hours, and it will still only get to 212 degrees.

“To kill Clostridium botulinum spores in low-acid foods, you need to get the temperature up to 250 degrees, and the only way to do that is to use a pressure canner.”

Official home food preservation guidelines, available online at the National Center for Home Food Preservation, are periodically updated, Carter said. So if you are following old guidelines, you aren’t getting the most accurate information.

For example, tomatoes used to be considered a high-acid food, but today’s varieties are often right on the line between high-acid and low-acid, so citric acid or vinegar must be added to them before being canned.

Also, standard household vinegar is now often a lower strength than it used to be, Carter said, so following old recipes, possibly passed down for generations, that call for vinegar to acidify a food for water bath canning may not provide the margin of safety necessary.

Many people, Carter said who have canned for years — even decades — are unaware of new recommendations. And, surprisingly, she added, canning methods portrayed on televised food shows, websites and even in some cookbooks are often improper.

“People don’t know what they don’t know,” Carter said. “So we’ve been trying to get information out to people. It’s important.”