If you’ve been planning to can your garden harvest this year, no doubt some well-meaning soul has warned you about botulism. Or maybe not. Botulism rumors seem to fall into one of two categories, either:
1. Doom and Gloom – The “home canning is a dangerous activity that will kill you” approach. Or
2. Ostrich Approach – Otherwise known as the “those botulism stories are just old wives’ tales.”
As with most things, the truth falls somewhere in between. Foodborne botulism is a very real possibility with serious results. But home canning is not inherently dangerous or risky as long as we follow some basic safety rules.
What is botulism?
Botulism is an illness caused by the Clostridium botulinum bacteria, which makes its home in the soil. Unlike most bacteria, C. botulinum can exist in a spore state that, like cockroaches, is resistant to most extermination attempts. In fact, once those spores find a comfortable environment they start growing and produce one of the most deadly toxins known to man. C. botulinum is most at home in moist, low-acid foods, with little oxygen, and between 40 – 120 degrees.
How common is botulism poisoning?
There are anywhere from 20 – 40 cases of foodborne botulism in the United States each year. Most foodborne cases are caused by improperly stored fish and seafood at home, potatoes baked in foil and not refrigerated, and home canned foods. Home canned foods that have recently caused botulism include corn, green beans, asparagus, tuna and other fish, kimchi, beets, and homemade soups and sauces.
Twenty to 40 cases of botulism may not seem like a lot, but botulism can be deadly. Most of us like to share our home canned goods with friends and family. Do you want your food gifts to cause illness in others? No, me neither.
What are the signs and symptoms of botulism?
The signs of botulism in canned goods can vary. If your commercially canned item is bulging, choose to err on the safe side and always throw it away. Home canned goods that are infected may have a rancid odor when opened, but they may also have no signs at all. Any home canned food that was not processed correctly, or that has bubbling in the jar, or that has a foul odor, or that has mold growing in it, or that has popping jar lids (it happens!) should be disposed of immediately.
Botulism poisoning causes stroke-like symptoms. Even if the infection is not fatal, and there are fewer botulism deaths now than in the past due to an available anti-toxin, it may result in permanent nerve damage and or paralysis. The botulism toxin is serious stuff. It is though that one-half pound of the toxin would be enough to kill everyone in the U.S.
Why don’t I get botulism from fresh, cooked vegetables?
Although C. botulinum can be deadly, it’s also very picky about where and how it produces toxin. C. botulinum happily grows in the same soil as our corn and asparagus and other vegetables. But the spores will only produce the poisonous toxin in a low-oxygen environment. Fresh vegetables kept in the refrigerator are in a high oxygen environment. On the other hand, canned goods are low oxygen, since the canning process drives oxygen out of the can.
Other ways to control the toxin growth are:
- Freezing– the spores like a 40 – 120 degree temperature range, freezing falls below this
- Drying – the spores needs moisture to grow and produce toxin
- High-acid foods – high acidity prevents toxin development
- Correct heat – properly canned low-acid foods
How can I avoid botulism in home canned goods?
The threat of botulism can be scary, but it doesn’t have to be. It’s pretty easy to avoid all concerns of botulism poisoning without sticking your head in the sand. Driving a car can be a dangerous endeavor also, but we follow the rules and don’t drive 70mph in a 25mph zone. It’s the same with home canning, we just need to follow a few basic rules.
1. Process low-acid foods in a pressure canner, not a water bath canner.
2. Don’t make up your own recipes. Follow approved recipes.
3. Don’t process jars in the oven, use the pressure canner.
4. Adjust processing times for altitude.
5. If you still want more, join our Home Canning Expert Program and become confident that you are providing your friends and family with wholesome home canned goods, that aren’t going to make anyone sick!
Update: Our Home Canning Expert Program is no longer available, but you will find answers to all your canning questions in The Confident Canner. Download your copy today. It’s like having your grandmother standing by your side giving advice.
Hillers, Val & McCurdy, Sandy (Eds.). (2004). Food Safety Advisor Volunteer Handbook. Pullman, WA: Washington State University Extension.
Labuza, T.P. * Erdman, J.W. Jr. (1984). Food Science and Nutritional Health: An Introduction. St. Paul, MN: West Publishing Co.
Mehas, K. & Rodgers, S. (1989). Food Science and You. Peoria, IL: Glencoe Division, Macmillian/McGraw-Hill.
National Enteric Disease Surveillance: Botulism Annual Summary (2008-2011). Atlanta, GA. Centers for Disease Control and Prevention. Department of Health and Human Services.