HealthLink BC File #22, May 2012
Home Canning - How to Avoid Botulism
- What is botulism and how is it caused?
- What steps can I take to avoid botulism?
- What do I need to know about pressure canning?
- What jars are best for canning?
- What should you do if the home-canned food does not seem right?
- The importance of cleanliness
- For more information
What is botulism and how is it caused?
Botulism is a serious form of food poisoning that can cause death. The poison is produced by Clostridium botulinum, a bacterium that is commonly found in soil, or on raw fruits and vegetables, on meat and fish and many others foods and surfaces.
Botulism spores are tough, and cannot be killed with boiling water or heat without including canning pressures.
Botulism bacteria (the bacteria that grow out of germinated spores) can multiply quickly in a moist, oxygen-free environment and create a very powerful poison. One teaspoonful is enough to kill 100,000 people.
Improper home canning creates the perfect environment to grow botulism.
Because food contaminated by botulism may look and smell normal, you cannot tell by looking at the food whether it is poisoned by botulism bacteria.
What steps can I take to avoid botulism?
Home can properly using extreme care to avoid botulism. Do not take any short cuts.
High-acid foods are resistant to bacteria and only need the "boiling water bath" method of canning. Plums or rhubarb are high acid foods. The "boiling water bath" is a food preservation method commonly used in making jams. It involves dropping a basket of sealed jars into a large pot of rapidly boiling water. Low-acid foods such as most vegetables, meats and seafood must be canned at a higher temperature using a pressure canner.
What do I need to know about pressure canning?
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 116°C (240°F). 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 points in mind:
- Foods can be processed at 5, 10 and 15 pounds pressure. Consult a chart provided in the instructions to determine what pressure is safe for the food you are canning.
- Processing time will vary depending on the type of food being preserved and the size of the jar. Never shorten the cooking time that is recommended in the instructions.
- If you live more than 1,000 feet above sea level, the pressure and cooking time will have to be adjusted. Consult a chart.
- Once the right pressure level is reached during cooking, it must be kept constant throughout the cooking step.
- Both weighted gauges and dial gauges should be checked for accuracy. Read the manufacturer's directions carefully for recommended testing and frequency procedures, to make sure your canner is being operated safely and correctly.
What jars are best for canning?
It is important that you use heavy-duty jars made specifically for home canning.
"Mason" type 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 rims are perfectly smooth and there are no scratches or cracks that would prevent a perfect seal.
It is important that you do not use commercial jars, such as empty peanut butter jars for home canning. Commercial jars are not strong enough to be safely used.
What should you do if the home-canned food does not seem right?
Never eat, or even taste any home-canned food that:
- Appears to be spoiled;
- Develops a bad smell during cooking;
- Has a bulging container lid or is leaching;
- You are not sure if the food was properly canned or not.
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, container, or your hands may have touched.
The importance of cleanliness
All work surfaces and your hands should be kept clean during all stages of the canning process. The food being preserved must be rinsed clean. It is very 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 1 extra minute of boiling for each extra 1,000 feet of elevation. To sterilize tops, follow the manufacturer's instructions. Wash your hands often with warm soapy water.
For more information
Home canning is perfectly safe but needs to be done correctly. It is a good idea to read about home canning before you try it. Books are available on the subject, either at the library or in the stores. Pressure canners almost always come with instructions. If you have an older pressure canner and cannot find the instructions, contact the manufacturer for a copy.
An excellent source of information on home canning is the Utah State Canning Guide at extension.usu.edu/utah/htm/fcs/food-preservation-canning/usda_home_canning and at EatRight Ontario – Home Canning www.eatrightontario.ca/en/Articles/Cooking-Food-Preparation/Home-Canning.aspx
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