What Is Botulism?

Quick Answer

Botulism is a rare but serious illness caused by a toxin produced by the bacteria Clostridium botulinum. Improperly canned food contains this toxin, even if it looks and smells fine. To lower the risk, use tested recipes and follow every step of the canning process, including any adjustments needed for your elevation.

How Common Is Botulism?

Botulism is a rare but serious foodborne illness that can occur if you eat improperly canned food. The bacterium Clostridium botulinum forms spores, survival units that allow it to resist treatments such as boiling water. In improperly processed low-acid canned food, these spores can germinate, allowing the bacteria to grow and produce the toxin.

How Can I Prevent Botulism When Canning?

When canning, keep these rules in mind to help ensure you are canning your food safely:

Use a current, scientifically tested recipe.
Use the canning method listed in the recipe. Do not skip steps or change the canning method.
Use the correct processing time.
Use the correct pressure for your elevation (altitude) and type of pressure canner.
Do not make up your own canning recipe.
Do not add extra vegetables or thickeners to recipes unless the tested recipe allows it.
Add the correct amount of acid called for in tested tomato recipes.
Use the correct canning equipment.

Low-acid foods need pressure canning to destroy botulism spores. This includes meat and most vegetables. Use the full processing time and the pressure listed for your elevation. Let the steam vent for 10 minutes before pressurizing the pressure canner, and let the canner depressurize naturally after the processing time is completed.

Does the Age of a Filled Jar Tell Me Whether It Is Safe?

No. Safe canning and storage matter from the start. For the best quality, plan to use most home-canned food within a year. Follow any shorter storage limit in the tested recipe. Keep jars in a cool, dark, dry place.

Food can lose flavor, color, and texture over time. A jar does not become unsafe just because it has been in storage for longer than one year. But age and a sealed lid cannot ensure that food is safe to eat.

Label jars with the food and canning date, and use older jars first. Protect jars from freezing and from large temperature changes. USU's Storing Canned Goods guide explains storage conditions in more detail.

Is My Home-Canned Food Still Safe to Eat?

Do not taste food to find out whether it is safe. You cannot see, smell, or taste botulism toxin. If you are unsure whether the food was safely canned, do not eat it.

Before consuming a food that has been home-canned, check the following items, including:

The jar is properly sealed.
The jar is not cracked or damaged.
The food was processed using the correct method.
The correct processing time and pressure were used.
The proper altitude adjustment was made.
The jar was stored correctly.

Discard food if the jar leaks, bulges, has a broken seal, or shows mold or other signs of spoilage. Food can also be unsafe without these signs. Follow the National Center for Home Food Preservation's guide to handling spoiled canned food. Do not open a suspect jar just to smell or taste it.

How Does Adding Acid to Tomatoes Help Prevent Botulism?

Some tomatoes do not have enough acid for safe canning on their own. Adding the specified acid helps prevent the botulism bacteria from growing. For whole, crushed, or juiced tomatoes, add 1 tablespoon of bottled lemon juice or ¼ teaspoon of citric acid per pint. For quarts, use 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid. It is recommended to add the acid to the jar before filling it. Use bottled lemon juice, not fresh juice. Follow the fully tested tomato recipe, even when using a pressure canner. These amounts do not replace the acid instructions in salsa or other mixed-food recipes.