Growth of the bacterium Clostridium botulinum in canned food may cause botulism, a deadly form of food poisoning. These bacteria exist either as spores or as vegetative cells. The spores, which are dormant and comparable to plant seeds, can survive harmlessly in soil and water for many years. When ideal conditions exist for growth, the spores produce vegetative cells which multiply rapidly and may produce a deadly toxin within three to four days of growth in an environment consisting of:
- a moist, low-acid food
- a temperature between 40° and 120°F
- less than 2 percent oxygen
Botulism spores are on most fresh food surfaces. Because they grow only in the absence of air, they are harmless on fresh foods. Most bacteria, yeasts, and molds are difficult to remove from food surfaces. Washing fresh food reduces their numbers only slightly. Peeling root crops, underground stem crops, and tomatoes reduces their numbers greatly. Blanching also helps, but the vital controls are the method of canning and making sure the recommended research-based process times are used.
The processing times in this publication ensure destruction of the largest expected number of heat-resistant microorganisms in home-canned foods. Properly processed, canned food will be free of spoilage if lids seal and jars are stored below 95°F. Storing jars at 50° to 70°F also enhances retention of quality.
To further reduce the risk of botulism, home canned low-acid and tomato foods should be boiled even if you detect no signs of spoilage. Boil foods for 10 minutes at altitudes below 1,000 feet. Add an additional minute of boiling time for each additional 1,000 feet elevation. In Minnesota, boil food for 11 minutes.