Home-canned foods are responsible for over 90% of all cases of foodborne botulism.
What could be more delicious than a wintertime meal prepared with vegetables from your summer garden? Unfortunately, if not processed properly in a pressure canner, low-acid foods can support the production of the deadly botulism toxin.
A deadly toxin found on the surface of most fresh food
Clostridium botulinum bacteria are the main reason why low-acid foods must be pressure-canned to be safe. Clostridium botulinum is a common soil microorganism that produces a very deadly toxin or poison. Botulinum spores are on most fresh food surfaces, but because they grow only in the absence of air, they are harmless on fresh foods.
The conditions that favor the germination of these spores are low acidity (such as in vegetables and meats) and the absence of air (such as in a sealed canning jar). Clostridium botulinum spores can be destroyed by pressure canning the food at a temperature of 240 degrees Fahrenheit or above for a specific period.
Use a pressure canner for low-acid foods
- Red meats
- Fish
- Poultry
- All vegetables (except for most tomatoes)
Do not use water bath canning methods
A boiling water bath canner heats food to boiling temperature (212 degrees Fahrenheit), which is not high enough to ensure safety for canning vegetables and other low-acid foods. Water bath canning can be used for canning pickles or fruit.
If you find timetables on recipes for processing low-acid foods in a boiling water bath canner, do not use them. Research has shown that these timetables present a very real risk of botulism.
Use a pressure canner to prevent botulism
A pressure canner heats food to high temperatures (240-250 degrees F or higher) and destroys the spores that produce the botulism toxin. All vegetables to be canned must be washed thoroughly and peeled, trimmed or chopped as directed.
- Pickling or canning salt can be added for flavor but does not prevent spoilage.
- Spices and herbs may be added in small amounts.
- Never add butter, fat, flour, rice, barley or pasta unless the tested recipe directs you to do so.
- Adding ingredients that are not called for in the recipe may result in an unsafe product.
5 steps for preventing botulism in low-acid foods
Successful processing in a pressure canner requires attention to several details:
- Vent pressure canners for 10 minutes at the start of processing. Venting drives air from the canner. If air remains trapped in the canner, the canner will not reach pressure or pressurization will take a long time and a poor, unsafe product will be the result.
- Adjust for elevation. When pressure canning meats and vegetables, it is important to adjust processing pressure for elevation. The highest altitude in Minnesota is 2,000 feet.
- Keep an eye on pressure. Start counting processing time when the correct pressure is reached and regulate heat to maintain steady pressure. Bring the pressure back up and retime the entire process if at any time the pressure drops below the processing level. Fluctuating pressures can cause jars to lose liquid and damage seals or lead to under-processing and unsafe food.
- Do not force-cool the canner. Allow the canner to depressurize when the timed process is completed.
- Reprocess within 24 hours, if necessary. If jars fail to seal, remove the lid and check the jar-sealing surface for tiny nicks. If necessary, change the jar, add a new, properly prepared lid and reprocess within 24 hours using the same processing time. Otherwise, refrigerate the jars and use them within 2 to 3 days or freeze the jars for later use.
Reviewed in 2025