Botulism and Home Canning: What the CDC and USDA Say, and What to Do With a Suspect Jar

Reading about botulism can feel heavy when your shelves hold jars you're proud of. This page is not meant to scare you. Home canning has clear rules, and the CDC says you can prevent botulism by following safe canning instructions and using the right equipment. This page reports what the CDC, the USDA and the National Center for Home Food Preservation (the US canning experts at the University of Georgia, "the National Center" from here on) say. It is no substitute for medical advice. We add nothing of our own about symptoms or treatment.

What is botulism?

The USDA calls botulism a deadly kind of food poisoning. It comes from a germ, Clostridium botulinum, growing in canned food. The CDC says its toxin attacks the nerves. That can make breathing hard and cause paralysis. All types of botulism can be fatal.

The germ lives as spores on most fresh food, and the USDA says they're harmless there. Under the right conditions they grow and may make a deadly toxin within 3 to 4 days. The USDA names those conditions:

• a moist, low-acid food
• a temperature between 40°F and 120°F
• very little oxygen (less than 2 percent)

A sealed jar of low-acid food kept at room temperature can give them all three. That's why the USDA calls the canning method and the tested times the vital controls.

Why do low-acid foods need a pressure canner?

The USDA says low-acid foods must be canned in a pressure canner to be free of botulism risks. Low-acid foods (vegetables, meat, chicken, fish) include red meats, seafood, poultry, milk and all fresh vegetables except most tomatoes.

The USDA says the spores are very hard to kill at boiling-water temperatures. Low-acid foods should be heated to 240°F to 250°F, which takes a pressure canner. The CDC agrees. Pressure canning is the only recommended method for low-acid foods, and a boiling water canner does not protect against botulism in them.

The USDA adds that some tomatoes and figs have a pH just above 4.6, the low-acid line. To can them as high-acid foods, you must add acid, and a tested recipe tells you how. Our low-acid foods page has the list.

The CDC also names the machines it doesn't want used: electric multi-cookers, even with a canning button. See canning in an Instant Pot. The CDC describes a canner that holds at least four quart jars upright and has an accurate gauge. Whether a plug-in canner made just for canning fits that is an open question among the experts. See are electric pressure canners safe.

Why might a bad jar look fine?

The CDC says the toxin can't be seen, smelled or tasted, and even a small taste can be deadly. The National Center says low-acid foods may show little or no spoilage, and suspect jars should be treated as if they hold the toxin. A jar that looks normal has not passed a test. Your senses are not a safety check here.

A seal is not a test either. A seal does not show that the food got the heat it needed. Never taste a suspect jar.

The CDC does list signs that mean the food goes out, for home-canned and store-bought food alike:

• the container is leaking, bulging, swollen, cracked or damaged
• it spurts liquid or foam when opened
• the food is discolored, moldy or smells bad

The National Center adds dried food streaks on the outside of the jar, rising bubbles, and cotton-like mold on the food or under the lid. And the CDC's last word covers everything else: if you don't know whether safe canning steps were followed, throw the food out.

What should you do with a suspect jar?

Do not taste it. The National Center says the toxin can be fatal if swallowed or if it gets in through openings in the skin. Avoid contact with the contents. Its steps depend on the state of the jar. Please follow the National Center's page on spoiled canned food directly, because the details matter.

1. Check the state of the jar

   The National Center treats jars that are still sealed differently from jars that are unsealed, open or leaking.

2. Still sealed

   Put the jar in a heavy garbage bag, close it, and place it in the trash or a nearby landfill.

3. Unsealed, open or leaking

   These need to be made harmless before disposal, and you wear gloves. Its page gives the steps.

4. Clean up anything it touched

   The National Center gives a bleach-solution cleanup for counters, equipment and clothing, with gloves on. It also warns about the bleach itself.

Can boiling food make it safe to eat?

The CDC also recommends boiling home-canned tomatoes, foods made with them, and all low-acid home-canned foods before eating, as a safeguard. The boiling time depends on your altitude, and its page gives it. The CDC says high heat can destroy the toxin. This does not rescue a suspect jar. For those, the CDC's rule is to throw them out. And it doesn't replace correct canning.

What are the symptoms, and how is it treated?

The CDC lists trouble swallowing, muscle weakness, double or blurry vision, drooping eyelids, slurred speech, trouble breathing and trouble moving the eyes. Foodborne botulism may also bring vomiting, nausea, stomach pain and diarrhea. A person may not have all of these at once.

The CDC says botulism is treated with antitoxin. It stops further harm but can't undo damage already done. It works best early, which is why the CDC says to get care right away. Many patients are hospitalized, some need a breathing machine, and recovery can take weeks or months.

How common is it?

The CDC calls botulism uncommon but dangerous. It says home-canned vegetables are the most common cause of botulism outbreaks in the US. We didn't find a rate for home canning, so we give no number.

What keeps your jars safe?

• Match the method to the food. Low-acid food goes in a pressure canner, says the USDA.
• Use a tested recipe, exactly. Sources are the USDA Complete Guide, the National Center and your state's university extension office (free local food-safety advice), together with your machine's manual.
• Check your equipment. The CDC names an accurate gauge, clean lid gaskets, letting air out before pressurizing, and current processing times.
• Adjust for your altitude. See canning at altitude.

We publish no times or recipes, because those numbers already have an owner. A lid that failed is a separate question. See jars not sealing. If a canning question worries you, call your county extension office. For symptoms, the CDC says to see a doctor or go to the emergency room.