Beat botulism with safe home food preservation

Sarah Francis
Iowa State University Extension and Outreach

AMES, Iowa — Interest in home food preservation boomed this summer and fall due to the pandemic.

With so many people preserving food at home for the first time, there is concern about botulism outbreaks. Improperly home-canned, preserved or fermented foods can provide the right conditions for botulinum, the bacteria that causes botulism, to grow. In November, five people in Colorado became sick with botulism after consuming home canned foods. This is an important reminder to follow safe food handling and research-based food preservation recipes, said Sarah Francis, associate professor and nutrition and wellness state specialist with Iowa State University Extension and Outreach.

Botulism is a rare, but very serious condition that is caused by very poisonous toxins, Francis said. Clostridium botulinum spores — “botulism spores” — are very hard to destroy at boiling-water temperatures. These dangerous bacteria are responsible for causing botulism. The higher the canner temperature, the more easily the spores are destroyed.

Botulism symptoms usually start with weakness of the muscles that control the face, mouth, eyes, and throat. This weakness may spread to the neck, arms, torso and legs. Botulism also can weaken the muscles involved in breathing, which can lead to difficulty breathing and even death, Francis said.

“If you have home canned foods, do not open, smell, touch or eat any food from jars that are damaged, leaking or swollen, that squirt liquid or foam when opened, or containing food that looks or smells bad. If you are ever unsure whether food is safe, throw it away. Also, boil home-processed, low acid foods, like tomato sauces, meats, soups and vegetables, for 10 minutes in a saucepan before serving even if there is no sign of spoilage,” Francis said.

To ensure the safety of your future home preserved foods, follow these tips to lower the risk of botulism in the future.

Use only research-based recipes and instructions: These recipes have been tested to ensure spores are killed when heated long enough at a specific temperature. The acidity level of foods determines the type of canning method needed to destroy these spores. Francis recommends the following research-based resources for recipes:

ISU Extension and Outreach,

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  • National Center for Home Food Preservation So Easy to Preserve (Sixth Edition),
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  • USDA Complete Guide to Home Canning (2015),
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Use the correct canner for the recipe — Water bath canner for high acid foods, pressure canner for low acid foods.

Follow the research-based, tested recipes exactly, making sure to adjust the processing times for altitude as needed.

To learn more about safe home food preservation, visit ISU Extension and Outreach’s Preserve the Taste of Summer website at You can also call AnswerLine with any immediate questions, Monday through Friday, 9 a.m. to noon and 1 to 4 p.m. at 1-800-262-3804.

Canned green beans in glass jars.