Botulism & Home Canning: Safety Rules

We research products independently. When you buy through links on this page, we may earn a commission from Amazon at no extra cost to you. As an Amazon Associate we earn from qualifying purchases. Learn more.

Botulism in canning comes from one bacterium, Clostridium botulinum, whose spores survive boiling water and can make a deadly toxin inside a sealed jar of low-acid food. The fix is well established. The USDA says low-acid foods must be processed at 240 to 250°F (116 to 121°C), which takes a pressure canner run at 10 to 15 psi, using a tested time for your food, jar size and elevation. The CDC puts it simply: "Pressure canning is the only recommended method for canning low-acid foods."

This guide explains the risk using only CDC and USDA sources, plus the National Center for Home Food Preservation (NCHFP), which maintains the USDA canning guidance. It covers which foods are at risk, why the rules look the way they do, and what to do with a jar you don't trust.

This page is general safety information, not medical advice. If you think someone has botulism, get emergency care now.

What Botulism Is

The CDC describes botulism as a rare but serious illness caused by a toxin that attacks the body's nerves. It can cause difficulty breathing, muscle paralysis and even death. The toxin is made by Clostridium botulinum and, sometimes, two related bacteria.

The CDC lists five main types: foodborne, wound, infant, iatrogenic (from injected toxin) and adult intestinal toxemia. This page is about foodborne botulism, and the CDC names homemade foods that have been "improperly canned, preserved, or fermented" as a common source. Store-bought foods can be a source too, but the CDC calls that uncommon.

About 5% of patients die, according to the CDC's clinical overview. Prompt treatment with antitoxin matters.

How Botulism in Canning Happens

Botulinum spores are on most fresh food surfaces, per the USDA. On fresh food they're harmless, because they only grow without air. The USDA says the spores produce cells that multiply and can make toxin within 3 to 4 days in an environment with:

• a moist, low-acid food,
• a temperature between 40 and 120°F (4 and 49°C),
• less than 2 percent oxygen.

A sealed jar of green beans on a pantry shelf ticks all three boxes. That's why the canning process itself is what has to destroy the spores.

Washing doesn't solve it. The USDA says washing reduces microorganisms only slightly. Peeling root crops and tomatoes helps a lot, and blanching helps, but "the vital controls" are the canning method and the research-based process times.

Low-Acid vs Acid Foods: The Line at pH 4.6

Whether a food goes in a water bath or a pressure canner depends on its acidity.

Tomatoes and figs are borderline. The USDA says some have pH values slightly above 4.6, so tested recipes have you add lemon juice or citric acid. The CDC also lists some tomatoes among low-acid foods. Mixtures of acid and low-acid foods are usually low-acid too, unless a tested recipe adds enough acid.

Our guide to pressure canning vs water bath canning goes deeper on which foods need which method.

Why a Water Bath Isn't Enough for Low-Acid Foods

Botulinum spores are very hard to destroy at boiling-water temperature. The USDA says the higher the canner temperature, the more easily they're destroyed:

• At 240 to 250°F, the time needed to destroy bacteria in low-acid canned food ranges from 20 to 100 minutes, depending on the food, the pack and the jar size.
• In a boiling water canner, the USDA says safe processing of low-acid foods would take 7 to 11 hours.

At sea level, the USDA says a pressure canner at 10.5 psi reaches 240°F inside, in pure steam. Two things lower that temperature: higher elevation and trapped air. That's why every tested process requires venting the canner for 10 minutes and raising the pressure as your elevation rises. Our pressure canning altitude chart has the USDA pressure bands.

The Safety Rules That Prevent Botulism

These come from the CDC's home canning guidance and the USDA Complete Guide to Home Canning.

1. Use only tested recipes. The CDC says to follow the USDA Complete Guide to Home Canning and not to use other recipes, "even if you got them from a trusted friend or family member." Follow each recipe's ingredients, jar size, headspace and time exactly.
2. Pressure can all low-acid foods. Vegetables, meats, poultry, fish and soups go in a pressure canner, never a water bath.
3. Use a real pressure canner. The CDC says electric multi-cookers aren't adequate for canning low-acid foods, even ones with a canning button. The NCHFP says the same about appliances such as the Instant Pot. Our article on pressure cooker canning explains why.
4. Adjust for elevation. The USDA says using sea-level times or pressures at 1,000 feet or more can lead to spoilage.
5. Vent the canner for 10 minutes before pressurizing, so trapped air doesn't lower the temperature.
6. Keep the pressure up for the whole time. If it drops below the target, the USDA says to bring it back up and restart the full process time.
7. Test dial gauges every year. The USDA says a gauge that reads high causes under-processing, and one that's off by more than 2 pounds should be replaced.
8. Acidify tomatoes, even in a pressure canner, as the tested recipes require.
9. Let the canner cool on its own. The USDA says force-cooling can result in unsafe food or spoilage.
10. Store jars properly. The CDC says to label and date jars and keep them in a cool, dark place away from heat and sunlight. The USDA says to store them below 95°F (35°C).

Our beginner's guide to using a pressure canner walks through rules 4 to 9 step by step.

Methods That Raise the Botulism Risk

The USDA and NCHFP flag these as not recommended:

• Open-kettle canning (filling hot food into jars and sealing without processing). The USDA says it doesn't reach temperatures high enough to destroy all spoilage and food poisoning organisms.
• Oven, microwave and dishwasher "canning."
• Dry canning raw vegetables without the covering liquid. The NCHFP says it can lead to under-processing and a risk of botulism, and that the toxin can be present without visible changes or odors.
• Canning powders and aspirin. The USDA says canning powders are useless as preservatives, and the NCHFP says aspirin can't be relied on to prevent spoilage.
• Adding vinegar to fresh vegetables to shorten processing. The NCHFP says that doesn't work, outside of tested pickle recipes.
• Untested products such as pumpkin butter, canned butter, bread in a jar and herb-infused oils. The NCHFP has no canning process for any of them.

A Real Outbreak

In June 2024, eight people in Fresno County, California, got botulism after a family gathering. The CDC's report, published in MMWR in July 2025, traced it to a salad made with home-preserved prickly pear cactus pads (nopales).

The jars had been immersed in boiling water while empty, filled with raw chopped nopales and a little salt, sealed with new lids and stored for six weeks in a shed without air conditioning. No pressure canning was used. All eight patients were hospitalized, six in intensive care, and all received antitoxin. All survived.

It's a textbook case: a low-acid food, no tested process, and warm storage.

How to Spot a Suspect Jar

The USDA says to check every jar before you use it:

• The lid: it should be tight and concave. A bulging or unsealed lid is a warning sign.
• The outside of the jar: look for streaks of dried food running down from the top.
• The contents: rising air bubbles or unnatural color.
• When you open it: an unnatural smell, spurting liquid, or cotton-like mold (white, blue, black or green) on the food or under the lid.

The CDC adds jars that leak or are cracked, and food that's discolored, moldy or smells bad. Its rule is short: "If in doubt, throw it out!"

The hard part: the USDA says spoiled low-acid foods, including tomatoes, "may exhibit different kinds of spoilage evidence or very little evidence." A normal-looking jar isn't proof of safety, which is why you never taste food from a jar you suspect.

How to Dispose of Suspect Jars Safely (USDA)

The USDA says to treat every suspect container of low-acid food, including tomatoes, as if it contains botulinum toxin.

If the jar is still sealed: put it in a heavy garbage bag, close it, and place it in a regular trash container or take it to a nearby landfill.

If the jar is unsealed, open or leaking, detoxify it first:

1. Wear disposable rubber or heavy plastic gloves.
2. Carefully lay the jars and lids on their sides in an 8-quart or larger stockpot, pan or boiling water canner.
3. Wash your gloved hands thoroughly.
4. Add water carefully, without splashing, until it covers the containers by at least 1 inch.
5. Cover the pot, bring it to a boil and boil for 30 minutes.
6. Cool, then discard the jars, lids and food in the trash or at a landfill.

Clean up the area: the USDA says contact with botulinum toxin can be fatal whether it's swallowed or enters through the skin. Wearing gloves, treat every surface and tool that touched the food, including can openers and clothing, with a fresh solution of 1 part unscented household chlorine bleach (5 to 6% sodium hypochlorite) to 5 parts water. Let it stand 30 minutes, wipe it up with paper towels and bag them. Apply the bleach solution again, let it stand another 30 minutes and rinse. Then wash everything thoroughly and throw away the gloves. Don't breathe the bleach or let it touch your skin.

Boil Before You Eat

As an extra layer of protection, the CDC recommends boiling home-canned low-acid foods and home-canned tomatoes before eating:

This is a backup, not a replacement for proper processing. Never taste a jar first to decide.

Symptoms and What to Do

The CDC lists these botulism symptoms:

• Difficulty swallowing
• Muscle weakness
• Double vision or blurry vision
• Drooping eyelids
• Slurred speech
• Difficulty breathing
• Difficulty moving the eyes

Foodborne botulism may also cause vomiting, nausea, stomach pain or diarrhea. The CDC notes people may not have all the symptoms at the same time.

The CDC calls botulism a medical emergency: see a doctor or go to the emergency room immediately, and don't wait. Tell the doctor what home-canned food was eaten. Treatment is an antitoxin. The CDC's guidance for clinicians is to call the state health department right away for a consultation and, if it supports botulism, to request antitoxin immediately.

Get the Right References and Equipment

The USDA Complete Guide to Home Canning is free from the NCHFP website, and Purdue Extension sells the official printed edition. Our guide to the best canning books explains which books follow tested methods. For the canner itself, our best pressure canner guide compares models that meet the USDA's four-quart-jar minimum.

FAQ