Botulism and Food Poisoning in Home Canned Foods - Causes and Prevention
What is Botulism?
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 rare but 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 can you tell if there is botulism in your home canned foods, like green beans?
The answer is, unless you have access to a food science laboratory, 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 United States, an average of 145 cases are reported each year. Of these, approximately 15% are foodborne, 65% are infant botulism, and 20% are wound. Adult intestinal colonization and iatrogenic botulism also occur, but rarely. Outbreaks of foodborne botulism involving two or more persons occur most years and usually caused by eating contaminated home-canned foods. The number of cases of foodborne and infant botulism has changed little in recent years, but wound botulism has increased because of the use of black-tar heroin, especially in California.
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 frequently been from home-canned foods with low acid content, such as carrot juice, asparagus, green beans, beets, and corn.
However, outbreaks of botulism have resulted from more unusual sources. In July, 2002, fourteen Alaskans ate muktuk (whale meat) from a beached whale, and eight of them developed symptoms of botulism, two of them requiring mechanical ventilation . Other sources of infection include garlic or herbs stored covered in oil without acidification, chili peppers, improperly handled baked potatoes wrapped in aluminum foil, and home-canned or fermented fish. 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. a potato should be COOKED at the given time.
What are the Symptoms of Botulism Poisoning?
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.
In all cases illness is caused by the toxin made by C. botulinum, not by the bacterium itself. The pattern of damage occurs because the toxin affects nerves that are firing more often.
Where does botulism come from?
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.
Why is botulism a concern in home canning? My kitchen is clean and everything gets sanitized!
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.
How can botulism be prevented?
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. Colorado State University says:
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.
The processing times in recipes in PickYourOwn.org are from the USDA and Ball Blue Book, and ensure destruction of the largest expected number of heat-resistant microorganisms in home-canned foods. Properly processed, home canned food will be free of spoilage if lids seal and jars are stored below 95°F. Storing jars at 50° to 70°F also enhances retention of quality.
See this page for why and how to choose a canner and see this page for canning recipes that are based on the USDA recommendations.
Can't I simply heat the jars in a water bath canner for a very long time or add acid (vinegar or lemon juice)?
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.
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.
Why can't I use my own recipe?
How would you know it was safe? How ling should you process it? What type of canner? How could you be sure the botulism spores were destroyed (you can't see them with the naked eye)?
In addition to the acidity of the food and the heat resistance of the microorganism, the time required for sufficient heat to penetrate all parts of the food in the jar must be considered. Heat is transferred from the outside of the jar through the food and thus is affected by:
- The size and shape of the container. Smaller jars heat faster than wider or taller jars. The USDA no longer recommends jars larger than a half gallon, and typically jars must be 1 quart or smaller.
- Amount of liquid. Food containing a large amount of free liquid heats much more quickly than a more solid product.
- Piece size. Smaller pieces of food (corn, peas) heat much more quickly than large chunks.
- Amount of fat. Fat insulates the food and slows heat transfer. Most canning recipes require little or no added fats or oils.
- The type of heating medium being used. Wet steam heats faster than dry air.
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.
Are home-canned foods the only concern?
Infant botulism is a concern for children under one year of age. It is possible for bees to pick up the botulism spores from flowers or soil. These spores are not destroyed during the processing for honey. The botulism spores grow in the baby's intestinal tract and then produce the toxin. After the age of one year, this no longer happens because of higher acid levels in the baby's tummy. This is why you should not give babies (under 1 year old) any honey!
Flavored oils can be a special concern if not prepared correctly. When herbs, garlic, or tomatoes are placed in oils, the botulism spores on the plant material can start to produce the toxin in this anaerobic (oxygenless) mixture. To be safe, keep these flavored oils refrigerated and make only the amount of herbal oils and butters that will be used in a few days. Using dried herbs and vegetables will also reduce the risk.
Baked potatoes wrapped in foil and kept at room temperature can also form the anaerobic conditions the botulism spores need to produce their toxin. For this reason, leftover potatoes should be refrigerated. Potato salad made from leftover baked potatoes has been implicated in botulism poisoning.
What precautions should I take?
- 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. (All recipes on PickYourOwn are from these, unless specifically noted)
- 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.
- National Center for Disease Control, Center for Disease Control and Prevention (CDC)
- U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Foodborne Pathogenic Microorganisms and Natural Toxins Handbook, The Bad Bug Book.
- Clemson University Extension.
- Ohio State university Extension
- Oil Infusions and the Risk of Botulism, Colorado State University Cooperative Extension, Safefood new - Summer 1998 - Vol 2 / No. 4
- "Botulism Linked to Baked Potatoes".
- " Safe Home Canning of Fruits, Vegetables and Meats" - University of Minnesota
For more information on food borne illness, contact your local county Extension Agent (click here to find your county ext agent).
Examples in the news:
Botulism blamed on improper home-canning
February 27, 2009 - The Spokesman-Review, John
Stucke - "A serious case of botulism in Spokane has prompted warnings
from food preservation experts and health officials to follow strict
safety rules when canning vegetables at home. A nurse in her 30s,
along with two children younger than 10, were stricken with the nerve
toxin after eating improperly canned green beans from a backyard
garden. All three were given an antitoxin that was flown to Spokane
from a special storage facility in Seattle. Special precautions must
be taken when canning low-acid foods such as green beans and
asparagus. Since most vegetables don’t have enough natural acidity to
kill the bacteria, they must be canned using a pressure canner that
can reach high temperatures. Or, vegetables may be pickled with
enough vinegar to inhibit growth of the bacteria. As a safety
precaution, canned vegetables should be boiled for 11 minutes at
Spokane’s elevation before eating. Foods that were not canned
following U.S. Department of Agriculture standards should be thrown
away before opening."
Click here for the full story.
Botulism in garlic with oil / refrigerated without heat processing first
Three people were hospitalized with botulism after eating a chopped garlic-in-oil mix that had been used in a spread for garlic bread in Kingston, New York. The bottled chopped garlic spread relied solely on refrigeration to ensure safety. The FDA has ordered companies to stop making the product. Most of the 10 to 30 outbreaks reported annually in the United States are associated with home canned foods. Occasionally, commercially produced foods have been involved in outbreaks. Source: The Bad Bug Book (US Government publication)