Home Canning, Food Safety, and Botulism

Home canning, food safety, and botulism—don’t freak out, but do process safely

By Diane Wright Hirsch


cold pack green beansAs an Extension educator, I have been teaching folks how to can for more than thirty years. And still, what worries folks the most is botulism poisoning. While it continues to be very rare, when it does occur, it is often associated with improperly home canned food. So, it makes sense to keep the possibility of this deadly toxin in the back of your head when canning.

In April of this year, a deadly botulism outbreak reminded us of how important it is to use methods for home canning that are tested for safety and recommended by science based resources. At a pot luck event at a church in Ohio, patrons were served potato salad that had been made from home canned potatoes. It turns out that the home cook had used a water bath process—which is inappropriate for low acid foods like potatoes. Twenty-nine cases of botulism were identified out of the 77 attendees. Twenty-five met the case definition and were given botulinum anti-toxin. One person died.

Botulism is caused by Clostridium botulinum bacteria. These bacteria live in the soil where we grow fruits and vegetables. In order to produce toxin, the bacterium needs an environment that is low in acid, moist, and free of oxygen. Therefore, this is not a hazard to foods that are safely canned in a water bath canner. Most fruits, pickles, and other properly acidified foods with a pH of less than 4.6 do not provide the environment conducive to toxin formation—they are too acidic. That is why these foods ARE safely canned in a water bath canner that reaches 212 degrees F during processing (or the boiling point of water).

Low acid or high pH foods (4.6 or greater) are another story. C. botulinum is a spore former. This means that when it is confronted with a hostile environment (heating in a canner), it forms a spore or coat to protect itself. This spore cannot be destroyed by temperatures at the boiling point of water associated with a water bath canner. If a water bath canner is used to can low acid foods, the spores will survive the heating, then they will germinate once the jar is placed on the shelf. These bacteria will then produce the deadly neurotoxin in the moist, oxygen free canning jar environment. Only a pressure canner can provide enough heat to destroy the spores—temperatures at 240 degrees F.

Home food processors need also to be reminded that they are not commercial processors. They do not have access to commercial equipment, additives and other processes that can render some food products safe from the botulism toxin. In addition, commercial processors must adhere to strict US Food and Drug Administration (FDA) rules and follow science based recipes and processes that they have proved-in advance of production-to be safe. So think twice before developing your own recipes for canning low acid or acidified foods at home.

Follow these basic rules for safe canning and there is no reason to fear botulism, home canning, or, for that matter, the use of a (preferably) newer model pressure canner, which has all sorts of safety mechanisms built in.

  • Jams, jellies and preserves are safely canned in a water bath canner. These products generally have a low water activity that contributes to safety and shelf life.
  • Fruits are generally acidic and safely canned in a water bath canner.
  • Spoilage organisms such as yeasts and molds can still be a problem in water bathed foods if not canned using methods tested for safety.
  • Tomatoes are a special case. They are often borderline in pH—sometimes exceeding 4.6. It is recommended that you add 1 tablespoon of bottled, commercial lemon juice or ¼ teaspoon of citric acid to pint jars or 2 tablespoons of lemon juice and ½ teaspoon of citric acid to quart jars as an “insurance policy” to ensure that the pH is low enough to process in a water bath canner. Current recommendations for water bath canners range from a 45-minute process (water added) to an 85-minute process (straight-up tomatoes)! It actually makes more sense to process tomatoes in a pressure canner—times are just about half that in a water bath.
  • Acidified foods such as pickles, pickled vegetables or fermented foods rely on the acidifying process to bring the pH to the range for safe canning in a water bath canner. (The addition of vinegar or the process of fermentation that creates lactic acid are examples of acidifying processes.) Be sure in this case to only use tested recipes. Never add a few more cucumbers or a bit less vinegar. You are risking raising the pH to levels that botulinum may find attractive.
  • ALL other foods MUST be canned in a pressure canner. Carrots, green beans, corn, and yes, potatoes; meats, fish, poultry; mixtures that might include tomatoes and low acid ingredients such as a meat sauce or spaghetti sauce with onions and peppers; and any foods made from these foods—soups, stews, etc.

Finally, keep in mind that home canned foods should never find their way into a commercial operation, retail store or restaurant. You cannot sell them in Connecticut, unless you are a farmer who can make and sell jams, jellies, and acidified foods such as pickles. And, it would be wise to ban them from church suppers, potlucks, bake sales and other similar volunteer food events. You just never know if a well-meaning home canner has followed the right directions.

For more information about safe home canning, visit the National Center for Home Food Preservation at www.uga.edu/nchfp or the University of Connecticut Food Safety web page at www.foodsafety.uconn.edu.