As gardens begin producing tomatoes, green beans, peppers and other summer favorites, many home cooks are preparing to preserve their harvest through canning.
Home canning can be a safe and rewarding way to store food for months or even years. However, food safety experts warn that improper canning techniques can create conditions that allow dangerous bacteria, including Clostridium botulinum, to grow, which produces the toxin responsible for botulism poisoning.
Although botulism is rare, it can cause paralysis, respiratory failure and death. Botulinum toxin cannot be seen, smelled or tasted.
“Home canning is one of those food preservation methods where following tested procedures is critical,” according to guidance from the Centers for Disease Control and Prevention and the U.S. Department of Agriculture.
Why botulism remains a concern
Botulism occurs when Clostridium botulinum grows in oxygen-free environments and produces a potent nerve toxin. Improperly canned foods can provide the ideal conditions for the bacteria to grow.
Symptoms of foodborne botulism can include:
Double or blurred visionDrooping eyelidsSlurred speechDifficulty swallowingDry mouthMuscle weaknessDifficulty breathing
Symptoms can begin hours or days after consuming contaminated food. Anyone experiencing these symptoms after eating home-preserved foods should seek immediate medical attention.
Pressure canning versus water bath canning
One of the most common mistakes in home canning is using the wrong canning method.
High-acid foods, such as many fruits, jams and jellies, can generally be processed using a boiling water bath canner.
Low-acid foods require a pressure canner to reach temperatures high enough to destroy botulism spores.
Low-acid foods include:
Green beansCornBeetsPotatoesAsparagusCarrotsMeatsPoultrySeafood
Many vegetables that come from backyard gardens fall into the low-acid category.
According to the USDA, pressure canning is the only recommended method for safely canning these foods.
Safe home canning tips
Food preservation experts recommend several basic precautions:
Use tested recipes. Follow recipes and processing instructions from trusted sources such as the USDA Complete Guide to Home Canning, the National Center for Home Food Preservation, and university extension programs.
Use the proper equipment — Ensure pressure canners are functioning correctly and follow manufacturer instructions for maintenance and calibration.
Inspect jars and lids — Discard jars with cracks, chips or other damage that could prevent a proper seal.
Follow processing times carefully — Processing times are based on extensive research and should not be shortened.
Adjust for altitude when necessary — Higher elevations often require different processing times or pressures.
Store canned foods properly — Keep jars in a cool, dry location and label them with the date they were canned.
When in doubt, throw it out
Food safety experts emphasize that consumers should never taste food to determine whether it is safe.
Discard home-canned foods if:
The container is leaking, bulging or swollenThe seal is brokenThe jar is cracked or damagedLiquid spurts from the container when openedThe food appears moldy, discolored or has an unusual odor
Even a small amount of the microscopic botulinum toxin can cause severe illness.
Trusted resources for home canners
Consumers looking for canning guidance should rely on science-based resources rather than social media trends or untested family recipes.
Among the most widely recommended resources are:
USDA Complete Guide to Home CanningNational Center for Home Food PreservationState and county cooperative extension programsUniversity food preservation courses and workshops
Many extension services offer free classes, online tutorials and updated guidance tailored to local growing conditions.
As harvest season ramps up across the country, food safety officials say a few extra minutes spent following tested procedures can help ensure that home-preserved foods remain both delicious and safe.