Safe Temperatures for Canning
At sea level, water boils at 212 °F. This is the processing temperature for all high-acid and pickled foods. It is the temperature at which molds, yeasts, and some bacteria are destroyed.
Low-acid, non-pickled foods are processed in a pressure canner at 250 °F. It is the temperature at which bacterial spores (botulinum) are destroyed. Botulism is odorless, colorless, and tasteless. In the case of an otherwise healthy adult, it mimics flu symptoms. In the case of a small child, an elderly adult, or a person with an impaired immune system, it may be fatal.
What is botulism?
Botulism is a rare but serious paralytic illness caused by a nerve toxin that is produced by the bacterium Clostridium botulinum. Food-borne botulism is caused by eating foods that contain the botulism toxin. Contracting botulism is a potentially fatal medical emergency.
The classic symptoms of botulism include double vision, blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth, and muscle weakness. Infants with botulism appear lethargic, feed poorly, are constipated, and have a weak cry and poor muscle tone. These are all symptoms of the muscle paralysis caused by the bacterial toxin.
If untreated, these symptoms may progress to cause paralysis of the arms, legs, trunk, and respiratory muscles. In food-borne botulism, symptoms generally begin 18 to 36 hours after eating a contaminated food, but they can occur in as soon as six hours or as late as ten days.
How common is botulism?
In the United States, an average of 110 cases of botulism are reported each year. Of these, approximately 25 percent are food-borne, 72 percent are infant botulism, and the rest are wound botulism. Outbreaks of food-borne botulism involving two or more persons occur in most years and are usually caused by eating contaminated home-canned foods.
Botulism can be prevented. Food-borne botulism has often been contracted from home-canned foods with low acid content, such as asparagus, green beans, beets, and corn. You should follow strict hygienic procedures to reduce the risk of contamination. Oils infused with garlic or herbs should be refrigerated. Potatoes that have been baked while wrapped in aluminum foil should be kept hot until served or refrigerated.
Also pay close attention to the canning instructions given in this or any canning guide. Extensive instructions on safe home canning can be obtained from county extension services or from the USDA.