Botulism and Food Poisoning

Botulism is the name of the type of food poisoning we get consuming the toxin produced by active Clostridium botulinium in foods. Botulism was formerly known as “Kerner’s Disease.” It was named after the man who signed the death certificate of people who ate contaminated sausage and died in an outbreak in Germany. In fact, botulism comes from the Latin word, botulus, which means sausage. Botulism is a serious foodborne disease. It can be fatal. There are two different types of botulism poisoning that we need to be concerned with: adult and infant botulism.

How do you know if there is botulism in your home canned foods?

You can’t.  In this news story, Lizann Powers-Hammond, a food safety and preservation expert with Washington State University Extension says: “People always want to know if they can look at a jar of food to know if it’s okay. But I can’t tell by looking. What I need to know is the food’s history. How it was canned.”


In the US, an average of 145 cases are reported each year.  Of these, about 15% are foodborne, 65% are infant botulism, and 20% are due to wounds.  Outbreaks of foodborne botulism involving two or more persons occur most years and usually caused by eating contaminated home-canned foods.

While commercially canned goods are required to undergo a “botulinum cook” at 121 °C (250 °F) for 3 minutes, and so rarely cause botulism (while home pressure canning equipment only can reach 240 °F), there have been notable exceptions such as the 1978 Alaskan salmon outbreak and the 2007 Castleberry’s Food Co. outbreak.

Foodborne botulism has more common from home-canned foods with low acid content, such as green beans, beets, and corn.

Persons who do home canning should follow strict hygienic procedures to reduce contamination of foods. Oils infused with garlic or herbs should be refrigerated. Potatoes which have been baked while wrapped in aluminum foil should be kept hot until served or refrigerated. Because the botulism toxin is destroyed by high temperatures, home-canned foods are best boiled for 20 minutes before eating. Metal cans containing food in which bacteria, possibly botulinum, are growing may bulge outwards due to gas production from bacterial growth; such cans should be discarded. Any container of food which has been heat-treated and then assumed to be airtight which shows signs of not being so, e.g., metal cans with pinprick holes from rust or mechanical damage, should also be discarded.


Normal symptoms of food-borne botulism usually occur between 12–38 hours after consuming the botulinum toxin. However, they can occur as early as 6 hours or as late as 10 days after.

Normal symptoms usually include dry mouth, double and/or blurred vision, difficulty swallowing, muscle weakness, drooping eyelids, difficult breathing, slurred speech, vomiting, urinary incontinence and sometimes diarrhea. These symptoms may continue to cause paralytic ileus with severe constipation, and will lead to body paralysis. The respiratory muscles are affected as well, which may cause death due to respiratory failure. These are all symptoms of the muscle paralysis caused by the bacterial toxin.


C. botulinum is found in soil all over the world. The bacteria have the ability to form a spore (like a tiny, microscopic seed) that is very resistant to heat and chemicals. The bacteria grow best anaerobically; that means it will grow without air. The spores activated in the absence of air (as is present in a jar or can of sealed food) produce a toxin. This toxin is the most deadly known to food scientists.


Clostridium botulinum bacteria exist either as spores or as vegetative cells. The spores, which are dormant and comparable to plant seeds, can survive harmlessly in soil and water for many years. When ideal conditions exist for growth, the spores produce vegetative cells which multiply rapidly and may produce a deadly toxin within three to four days of growth in an environment consisting of:

  • a moist, low-acid food (like meats, almost all vegetables – including peppers, green beans, corn, etc.)
  • a temperature between 40° and 120°F
  • less than 2 percent oxygen (which occurs in any jar of canned food)

Botulism spores are present on most fresh food surfaces. Because they grow only in the absence of air, they are harmless on fresh foods. Most bacteria, yeasts, and molds are difficult to remove from food surfaces. Washing fresh food reduces their numbers only slightly. Peeling root crops, underground stem crops, and tomatoes reduces their numbers greatly. Blanching also helps, but the vital controls are the method of canning and making sure the recommended research-based process times are used.


While the incidence is fairly rare, the death rate is high if not treated immediately. Prevention is obviously extremely important. Home canning should follow strict hygienic recommendations to reduce risks. Pressure canners should be used for all low-acid foods, but home pressure canners only reach 240 F, not 250 like commercial equipment, and are not hot enough to kill ALL of the spores. It is the destruction of the active bacteria, and destruction or substantial reduction in numbers of spores along with the creation of an environment that is less conducive to the growth of the remaining spores, that ensures safety.

The botulism spores can only be killed by the high heat which can be obtained in a pressure canner. Water bath canners cannot do this. The toxin (that is produced in anaerobic conditions) can only be destroyed by boiling; so if there is any doubt, boiling the food for 20 minutes after opening the jars adds an additional measure of safety, although this is not always practical.



Botulism spores are very heat resistant. They may be destroyed at boiling water temperatures, but extremely long times are required. The higher the canner temperature, the more easily and quickly they are destroyed.

Low acid foods

Therefore, all low-acid foods should be sanitized at temperatures of 240° to 250°F, attainable with pressure canners operated at 10 to 15 PSI. PSI means pounds per square inch of pressure as measured by a gauge. At these temperatures, the time needed to destroy bacteria in low-acid canned food ranges from 20 to 100 minutes. The exact time depends on the kind of food being canned, the way it is packed into jars, and the size of jars.

Acid foods

The time needed to safely process low-acid foods in a boiling water canner ranges from 7 to 11 hours. Such long processing times are not researched and are not recommended. Losses in nutrients and quality would be unacceptable. The time needed to process acid foods in boiling water varies from 5 to 85 minutes.


How would you know it was safe?  How long should you process it? In what type of canner?  How could you be sure the botulism spores were destroyed (you can’t see them with the naked eye)?

The many factors involved make it impossible to estimate the correct processing conditions for any food product. This is especially true for items which are mixtures of food with differing water content, piece size, fat content, or acidity as well as types and numbers of microorganisms present. The establishment of a correct, safe process requires laboratory research by trained scientists. It is best to have a great Canning Recipe Book as a resource before attempting to develop custom recipes.



  • Discard all raw or canned food that shows any sign of being spoiled.
  • Discard all bulging or swollen cans of food and food from glass jars with bulging lids.
  • Use only tested approved recipes (Ball Blue Book, USDA, University Extension service, etc).
  • Do not deviate substantially from the approved recipes.  Adding another teaspoon of spice or substituting one spice is usually fine, but changing base ingredients or substantially changing proportions or steps is dangerous, particularly with regard to acidifiers (lemon juice, vinegar, citric acid, etc.)
  • Do NOT invent your own recipe; unless you have access to a food science laboratory to culture and test it.
  • DO NOT TASTE food from swollen containers or food that is foamy or has a bad odor.
  • Process low-acid foods at temperatures above boiling (which can only occur under pressure) and for the recommended time for the size of can or jar you are using.
  • Do not assume that the pressure canners renders all low acid foods safe. Home pressure canners are not as hot as commercial equipment, so some food simply cannot be safely canned at home.  Pureed pumpkin and foods made from pumpkin puree, like pumpkin butter is a clear example of a food that is unsafe to can at home.
  • Do not assume that adding vinegar, lemon juice, citric acid, or other acids will make low acid foods safe to can in a water bath canner.
  • DO can low-acid foods in a pressure canner, following an approved recipe. Do not can low-acid foods in the oven, in water-bath, open kettle or vegetable cooker.
  • Clean all surfaces with chlorine/water solution (one tablespoon of bleach per gallon of water) that leaky containers may have contaminated . Then discard any sponges or cloths used for cleanup.
  • Do not give honey or foods with honey to infants under one year of age.

Prepare Your Family for Emergencies

Signup Now to Get Our Exclusive Newsletter with DIY tips, guides, and quizzes!!