Michigan State University Extension
Preserving Food Safely - 01600937
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 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 3 to 4 days of growth in an environment consisting of:
* a moist, low-acid food. * a temperature between 40 and 120 degrees Fahrenheit. * less than 2 percent oxygen.
Botulinum 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 recommended processing times ensure destruction of the largest expected number of heat-resistant microorganisms in home-canned foods. Properly sterilized canned food will be free of spoilage if lids seal and jars are stored below 95 degrees Fahrenheit. Storing jars at 50 to 70 degrees Fahrenheit enhances retention of quality.