Botulism
Botulism is a rare but serious illness caused by a toxin that grows in low-acid, airless food, such as badly home-canned vegetables or garlic in oil.
Botulism is a rare but serious illness caused by a toxin made by the bacterium Clostridium botulinum. Its spores are common in soil and on fresh produce and are harmless in themselves. In food that is moist, low in acid and cut off from air, and kept at room temperature, the spores can grow and make toxin. You cannot see, smell or taste the toxin.
Botulism is a medical emergency. Symptoms include blurred or double vision, drooping eyelids, slurred speech, trouble swallowing and muscle weakness. If you or someone else has these symptoms, get emergency medical help at once.
How to do it
These habits prevent botulism in a home kitchen:
- Can low-acid foods, such as vegetables, beans, meat, fish and stock, only by pressure canning, following a tested recipe.
- Add acid to tomatoes before water bath canning, as tested recipes tell you.
- Keep homemade garlic, herb or chili oils in the fridge and use them within 4 days, or freeze them.
- Keep vacuum-sealed and other airtight food in the fridge or freezer, just as you would without the seal.
- Keep baked potatoes wrapped in foil hot, or refrigerate them promptly. Do not leave them out at room temperature.
- Never give honey to babies under 12 months old. Their gut cannot yet stop spores from growing.
Why it works
Boiling water at 100°C (212°F) does not destroy the spores. Pressure canning reaches about 116°C (240°F), which does, when the processing time is long enough. Acid stops surviving spores from growing, which is why high-acid foods can be water-bath canned. Cold slows growth, and freezing stops it.
How to store it
Store canned food in a cool, dry place and check it before you open it. You cannot tell by tasting, so never taste food you are unsure of. Throw home-canned or commercial food away without tasting it if:
- The lid or can bulges or is swollen
- The jar or can leaks, or is cracked or deeply dented
- Liquid spurts out when you open it
- The food is foamy, moldy, cloudy or smells bad
Put it in a sealed bag in the trash, and wash any surface or hands it touched.
Common mistakes
- Canning low-acid food in a water bath, an oven or a slow cooker.
- Using an untested recipe, or cutting the acid in a tested one.
- Storing garlic in oil at room temperature.
- Trusting that food is fine because it smells fine.
Related terms
- Pressure canningPressure canning heats sealed jars to about 116°C (240°F) under steam pressure. It is the only safe home method for low-acid foods such as vegetables.
- Water bath canningWater bath canning preserves high-acid foods like jam, pickles and acidified tomatoes by boiling sealed jars. It is not safe for low-acid foods.
- HeadspaceHeadspace is the empty gap between the food and the lid of a jar or container. The right amount helps canning jars seal and stops frozen jars cracking.
- Vacuum sealVacuum sealing removes air from a plastic bag and seals it shut. It slows freezer burn and spoilage but does not make food safe at room temperature.
- Shelf-stableShelf-stable food can be stored unopened at room temperature, like canned goods, dried pasta and UHT milk. Many of them need the fridge once opened.
- Danger zoneThe danger zone is the temperature range where bacteria grow fastest, 4 to 60°C (40 to 140°F) in USDA guidance. Keep food out of it as much as you can.