Clostridium botulinum is a foodborne illness-causing microorganism that is the main reason why low-acid foods (foods with a pH greater than 4.6), must be pressure-canned for food safety.
Clostridium botulinum is commonly found in soil and when conditions are favorable, it produces a very deadly toxin. Botulinum spores are found on most fresh produce, but because they grow only in oxygen-free environments, they are harmless on fresh foods.
Why is it a concern for food safety?
Clostridium botulinum grows in oxygen-free environments with a pH above 4.6. When conditions are unfavorable, it forms spores, a dormant state that allows it to survive extreme conditions, including temperatures up to 250 degrees F. Once conditions become favorable again, the spores transform back into a vegetative (active) microorganism, capable of producing botulinum toxin.
Symptoms
The botulinum toxin is a neurotoxin, meaning it can impact your nervous system. Symptoms of botulism include:
- Vomiting
- Diarrhea
- Vision problems
- Difficulty swallowing
- Respiratory failure.
Symptoms require medical treatment, and if left untreated, symptoms can become very serious.
How to reduce your risk
Canning poses a particular risk because the process removes oxygen and seals the food in an airtight container. To prevent Clostridium botulinum, it is important to use the correct canning method. When canning, it’s important to always follow a science-backed recipe.
Always prepare ingredients as described in the recipe and do not add ingredients that are not in the recipe; this may result in an unsafe product. Spices and herbs may be added in small amounts.
Canning acidic and acidified foods
Acidic and acidified foods have a pH of 4.6 or less and can be safely canned using a water bath or atmospheric steam canner.
The low pH of the foods helps inhibit the growth of Clostridium botulinum. While this canning method does not destroy the spores, the acidic environment prevents them from transforming into vegetative (active) microorganisms.
Acidic foods
Because acidic or high-acid foods naturally have a pH of 4.6 or less, these foods generally do not require the addition of acidic ingredients for safe canning. They include:
- Strawberries
- Blueberries
- Oranges
- Blueberries
Acidified foods
Acidified foods have had their pH lowered to 4.6 or less by the addition of acidic ingredients (lemon/ lime juice, citric acid and vinegar). For example, carrots have a pH above 4.6; however, when pickled with vinegar, they become an acidified food that can be safely canned in a water bath canner.
Canning low-acid foods
Low-acid foods have a pH above 4.6 and must be canned using a pressure canner.
Pressure canners can reach 250 degrees F, which is hot enough to destroy Clostridium botulinum spores. A water-bath or atmospheric steam canner can only reach 212 degrees F and will not eliminate Clostridium botulinum spores. Low-acidic foods include:
- Red meats
- Fish
- Poultry
- All vegetables
When to report a foodborne illness in Minnesota
If you believe that you became sick from eating any food or beverage, alert the Minnesota Department of Health:
- Call 1-877-FOOD-ILL (1-877-366-3455)
- Submit your report using the confidential Foodborne and Waterborne Illness Report
- Or, email [email protected]
Reviewed in 2025