August 23, 2001

When Preserving Produce Beware of Botulism, Food Specialist Advises

With home canners moving into their busiest season, a food specialist at North Dakota State University is urging caution to avoid botulism.

"If canning is not done properly, you can actually create conditions that are very favorable to the bacteria that produce the botulism toxin," says Julie Garden-Robinson of the NDSU Extension Service. "Clostridium botulinum require an oxygen-free environment to grow. That’s just what they get in canned foods that haven’t been heat processed properly."

Inactive Clostridium botulinum spores are found in soil and water throughout the world. In spore form, they’re relatively harmless. Under the correct conditions however, the spores germinate into actively growing cells. As they grow, they soon overpopulate and die, producing the deadly neurotoxin that causes botulism.

In the past 75 years most outbreaks of foodborne botulism in the United States have been caused by foods improperly canned at home. Because Clostridium botulinum is sensitive to acid, the problem is most pronounced in low-acid foods, mostly fish and vegetables such as string beans, corn, beets, spinach, asparagus, chili peppers and mixtures of food.

"If you’re canning any foods, be sure to use up-to-date recipes and follow directions for time, temperature and pressure very carefully," Garden-Robinson advises. Although it may be tempting to use family recipes passed down from previous generations, she says that’s could be a dangerous practice. "Even the newer varieties of tomatoes are lower in acid than those grown decades ago. Updated recipes take those changes into account," she says.

Smoked fish can develop the oxygen-free, or anerobic, conditions that favor growth of the bacteria. So can the interior of sausage. Conditions capable of supporting Clostridium botulinum have also developed in other foods like chopped garlic in oil, foil-wrapped baked potatoes, sauteed onions, turkey loaves, meat stews and pot pies. Refrigeration or use of a preservative such as sodium nitrite is a key to preventing growth of the bacteria in these cases, Garden-Robinson says.

Other forms of spoilage in canned foods can lead to growth of Clostridium botulinum. The growth of yeasts, molds and other bacteria can reduce acid levels and create conditions favorable for its growth.

Symptoms of foodborne botulism usually appear within 12 to 72 hours after the contaminated food is eaten. The most significant symptoms are blurred double vision and difficulty in swallowing and speaking. There is no fever early in the disease.

"Unless a victim gets treatment soon after symptoms develop, death may result within three to seven days," Garden-Robinson says. "This is a form of poisoning that has to be taken very seriously." Improved detection methods and the ready availability of antitoxins have reduced the high death rate to around 10 percent in recent years.

Garden-Robinson offers some guidelines for preventing botulism.

• Clean foods well before cooking or processing. This reduces but does not remove all bacteria. Bacteria are still present in nearly every pint or unit of food to be cooked or canned.
• Be sure all home canning methods are up-to-date with current research-based recommendations and are properly adjusted for altitude.
• Process all home-canned meats and vegetables, with the possible exception of tomatoes, in a pressure canner at 240 degrees F for the time recommended in a current USDA research-based publication. At sea level, a pressure of 10 pounds per square inch (psi) is necessary to reach 240 degrees F. With each 1,000 feet rise in altitude an additional 1/2 psi is needed to achieve 240 degrees F. Have your pressure gauge checked on a regular basis
• Acidic foods, such as tomatoes and fruits, if properly selected and processed, do not support the growth of Clostridium botulinum and may be canned in a boiling water bath if current, research-based instructions are followed. Adding acid in the form of lemon juice or citric acid is recommended in all tomato products canned in a boiling water bath as a precautionary measure.
• Before using home-canned food, critically examine the product and container. A bulging lid or leaking jar are signs of spoilage and potentially, the presence of the botulism toxin. When you open the jar, look for other signs of spoilage such as spurting liquid, an off odor or mold.
• As an added precaution, boil all home-canned vegetables and meats without tasting for 10 minutes plus one minute per 1,000 feet above sea level (15 minutes at 5,000 feet). Boil home-canned spinach and corn 20 minutes before tasting. If the food looks spoiled, foams or has an off odor during heating, discard it.
• Dispose of all spoiled food in a place where it will not be eaten by children or pets. One sure way to prevent the spread of toxin is to boil suspect foods 30 minutes before disposing. This will ensure destruction of any toxin that might be present and prevent its spread.

For more information about home food preservation including research-tested recipes, contact your county office of the NDSU Extension Service or visit the NDSU Extension Service Web site at http://www.ag.ndsu.nodak.edu/food.htm .

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Source: Julie Garden-Robinson, (701) 231-7187, jgardenr@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu

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