Umm…what exactly is botulism? (Part II)

Botulism: Prevention

After reading last week’s entry you know where botulism comes from and the effects it has on people. But perhaps even more importantly, are you confident that you know how to prevent it?

There are essentially two ways to prevent botulism: 1) thermal destruction (heating) of spores and 2) inhibiting spores from germinating into toxin-producing vegetative cells.

Even in favorable conditions, C. botulinum vegetative cells and toxin should be destroyed when held at the temperature of boiling water (212°F at sea level) for a relatively short period of time. There are some other inactivation heat processes available for different types of food, also.  However, C. botulinum spores are much more heat resistant and need temperatures much higher than boiling to be killed in  reasonable times.  For home canning, we use temperatures of 240°F or above. It is very important to note that, unlike most bacteria, C. botulinum and other spores are NOT destroyed by normal cooking or boiling procedures. The spores require higher temperatures (240°F or above) that properly operated pressure canners create.

dial=gauge pressure canner

To prevent botulism, use approved processing methods and times as recommended by USDA. Carefully follow recommendations for pressure canning low acid foods. If you are still concerned if you did everything right, you can boil home-canned products in a saucepan on the stove for ten minutes before serving (add one minute more for each 1,000 of elevation).

Also remember that C. botulinum spores cannot germinate and then produce the toxin in pH levels of 4.6 or below. Acid foods and properly acidified food products have pH levels equal to or less than 4.6, so the toxin formation is prevented. Examples of acidified foods include pickles to which vinegar is added and salsa to which lemon juice is added.

pickled green beanspeach apple salsa

You can further help prevent botulism and other foodborne illness by practicing general food safety; refrigerate all leftovers within 2 hours after cooking, and after just one hour if temperature is above 90°F. Discard, without tasting, any containers of food that are swollen, bulging, leaking, or cracked. Also immediately discard any product that spurts liquid or foam from a container once opened (unless it’s carbonated and shaken, of course).

Information in the entry comes from the USDA factsheet Clostridium botulinum and So Easy to Preserve.

3 thoughts on “Umm…what exactly is botulism? (Part II)

  1. Hannah

    In your article, you recommend boiling home-canned products for 10 minutes before serving, if one is unsure they have done everything right. I thought that toxins, once they are created by bacteria in food, are not destroyed by heat; only the bacteria are heat-sensitive. I was told this by my instructor in a Safe Food Handling course I took as part of my work in a restaurant. Could you please clarify this point?

    You also mentioned botulism in the foil-wrapped baked potatoes. One of our instructor’s many stories included the case of a man in Ontario who developed botulism from eating a few bites of a baked potato (baked in foil). Apparently, the foil creates an anaerobic environment where the botulinum spores can grow if held too long at the wrong temperature. The instructor called it ‘time/temperature abuse’. I no longer order baked potatoes when eating out, even though I love a good baked potato, not knowing how it’s been handled. But I do bake them at home.

    1. nchfp Post author

      Just as different bacteria and forms of bacteria require different amounts of heat to be destroyed, different types of bacterial toxins also vary in their sensitivity to heat. The bacterial toxins that cause many problems in foodservice are more heat resistant than the botulism toxin.

      Clarification on this point with regard to botulism can be found from the USDA Foodborne Illness & Disease Fact Sheet: Clostridium botulinum. As stated in said publication: “When the jars are stored at room temperature, the spores can germinate and produce the toxin. However, the toxin is sensitive to heat and can be destroyed if the food in question is boiled for 10 minutes (longer at high altitudes).”

      Both C. botulinum bacteria [in the vegetative form, not the spore form] and the toxin produced by the bacteria are sensitive enough to heat to be destroyed by boiling water in reasonable amounts of time. C. botulinum is found naturally in soils, marine environments and on surfaces in the open environment in the spore form, however. Spores of C. botulinum are very heat resistant and will not be destroyed by boiling water temperatures. The spores in home canning are destroyed by processes developed for temperatures of 240°F (at sea level) and higher. A reminder: this higher temperature can be created in pressure canners, but not boiling water canners.

      The Clostridium botulinum Fact Sheet is available at

Comments are closed.