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Botulism is a serious, often fatal form of food poisoning. The poison is produced by "Clostridium botulinum", a bacterium that is found everywhere -- in soil, on raw fruits and vegetables and on meat and fish. Over the years, a number of Canadians have died from botulism, as a direct result of improper home canning.
Botulism spores are resistant to heat -- even from boiling water -- and thrive in a moist, oxygen-free environment. As botulism spores reproduce, they generate one of the most extraordinarily powerful poisons on earth: one teaspoon-worth is sufficient to kill 100,000 people. Improper home canning creates the perfect environment in which to grow the botulism toxin. Because food contaminated by botulism may very well look and smell normal, there is often no warning. That is why home canning must be done properly with extreme care - any short cuts you take could be deadly.
Heat and acid level are the two keys to canning safety. High-acid foods such as plums or rhubarb are quite resistant to bacteria, and only require the "boiling water bath" method of canning. Low-acid foods -- including most vegetables, meats and seafood must be canned at higher temperatures, that only a pressure canner can attain.
The "boiling water bath" is probably what you saw your mother doing. It involves dropping a basket of sealed jars into a large pot of rapidly boiling water.
A pressure canner is a large, cast-aluminum pot with a locking lid and a pressure gauge. By cooking under pressure, you can bring the temperature of boiling water up to 116ºC (240ºF). This is the minimum temperature necessary to destroy botulism spores, and the only way to guarantee safe canning for food items such as vegetables, meats and seafood. Your pressure canner should come with complete instructions. Always follow them carefully. Keep these pointers in mind:
Manufacturers make heavy-duty jars specifically for home canning. Do not use, say, empty peanut butter jars, because commercial jars are not strong enough to be safely used for repeated home cannings. "Mason" jars -- which screw shut with a threaded neck are the most common choice. Do not re-use the lids: after a lid has been pried off once, a perfect fit can no longer be guaranteed. The jars themselves can be used many times, as long as the sealing rims are perfectly smooth and there are no scratches or cracks.
Never eat, or even taste any home-canned food that:
Place any questionable containers and food in a waterproof container and throw it in the garbage. Do not feed the questionable food to your pets or any other animals. After throwing it away, wash your hands well with warm soapy water. Also wash any utensils or surfaces the food or container may have touched.
The other safety factor to keep in mind is cleanliness. All work surfaces should be kept clean during all stages of the canning process. The food being preserved must itself be rinsed clean. It is particularly important to sterilize the jars and seals before use. To sterilize jars, boil them for 10 minutes. If you live at higher elevations (over 1,000 feet) allow one more minute of boiling for each extra 1,000 feet of elevation. To sterilize tops (seals with rubber gaskets) boil them for five minutes.
Home canning is perfectly safe ... but it needs to be done correctly. We recommend that you read up on home canning before you try it. Good books are available on the subject, either at the library or in the stores. Pressure canners almost always come with comprehensive instructions. If you have an older pressure canner and cannot find the instructions, contact the manufacturer to ask for a copy.
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