Home Canning - How to Avoid Botulism

HealthLinkBC File Number: 
Last Updated: 
October 2014

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, on raw fruits and vegetables, on meat and fish, and on many other 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 bacteria.

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?

To avoid botulism, you need to make sure you "home can" properly using extreme care. There are different methods of canning for high-acid and low-acid foods.

High-acid foods

High-acid foods are resistant to bacteria and only need the "boiling water bath" method of canning. Plums or rhubarb are examples of 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

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 increase the temperature of boiling water from 100°C (212°F) 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 300 metres (1,000 feet) above sea level, the pressure and cooking time will have to be adjusted because water boils at a lower temperature as altitude increases. 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.
  • Ensure the rubber seal on the canner lid is not broken or cracked. Replace if necessary.
  • Never open a canner when it is under pressure.
  • Do not cool jars in water, instead allow jars to cool slowly at room temperature.
  • Do not retighten lids.
  • Check seals.

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.

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;
  • foams;
  • develops a bad smell during cooking;
  • has a bulging container lid or is leaching; or
  • 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.

What are important steps to take when canning?

All work surfaces and your hands should be kept clean during all stages of the canning process. Use only good quality produce (fruits, vegetables) that do not have any cuts, bruises, or molds. 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. To sterilize tops, follow the manufacturer’s instructions. Wash your hands before you begin canning and 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 operating instructions, contact the manufacturer for a copy. Use new recipes when canning, as older recipes may not be tested for safety.

For more information, visit the following websites:

Is it an emergency?

If you or someone in your care has chest pains, difficulty breathing, or severe bleeding, it could be a life-threatening emergency. Call 9-1-1 or the local emergency number immediately.
If you are concerned about a possible poisoning or exposure to a toxic substance, call Poison Control now at 1-800-567-8911.

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