What is botulism and where does it come from?
Botulism is an illness caused by a toxin made by a bacterium that lives naturally in soil and on raw produce. The organism itself is common and usually harmless while it sits in dirt. The trouble starts when it ends up sealed in a place with no oxygen, a low-acid food and a temperature where it can grow.
That is why home canning is the usual setting for concern. A sealed jar of low-acid food is exactly the environment the organism wants, unless the processing step destroyed it first. The toxin cannot be seen, smelled or tasted, so a jar can look perfectly normal.
Infant botulism is a separate form tied to swallowing spores, and health agencies advise against giving honey to babies under one year. If you have questions about feeding infants, ask your pediatrician or public health office.
Which foods carry the highest risk?
Low-acid foods are the main worry. Think green beans, corn, beets, potatoes, meats, fish, soups and most mixed vegetable dishes. Fruits and properly acidified tomato products are less risky because acid holds the organism back, but only when the tested recipe is followed exactly.
Risk also shows up outside the jar. Oil infused with garlic or herbs, foil-wrapped baked potatoes left out, and homemade fermented fish are examples where low oxygen and low acid appear together without any canning at all.
- Home-canned low-acid vegetables and meats
- Garlic or herb oils kept at room temperature
- Cooked potatoes held warm in foil
- Soups and stews canned without a tested method
How do tested recipes prevent botulism?
Tested recipes are built from laboratory work that measured how heat moves through a specific food in a specific jar. They set the method, the ingredients, the headspace and the processing needed for that exact combination. Change one piece and the result is no longer tested.
For that reason this guide does not list times or pressures. Use a current recipe from the National Center for Home Food Preservation, the USDA Complete Guide to Home Canning or your county extension office. Low-acid foods need a pressure canner, which reaches heat a boiling water bath cannot.
A tested recipe also tells you what not to do. It will name the jar types, the headspace and the cooling steps. Treat these as part of the safety system, because each one supports the heat treatment that makes the food safe.
What mistakes cause most home botulism cases?
The pattern is consistent: an old family recipe, a shortcut on processing, an altered ingredient ratio, or a boiling water bath used for a food that required a pressure canner. Good intentions and years of past success do not change the science.
Another common error is trusting a jar because it sealed. A sealed lid shows that air was driven out. It does not show that the food was heated enough to be safe.
- Using a recipe from a decades-old book or a family card
- Adding extra onions, peppers or thickeners to a tested recipe
- Skipping the pressure canner for low-acid food
- Reusing jars with chips, or lids that failed
What should I check before eating home-canned food?
Inspect every jar before opening. Throw out anything with a bulging or leaking lid, spurting liquid when opened, cloudy or foamy contents, an off smell, or a lid that moves or lacks a firm seal. Do not taste to test.
Bad jars need careful handling because the toxin can be harmful in tiny amounts. Do not pour contents where pets, poultry or wildlife can reach them, and keep the jar away from skin and splashes. Your extension office can explain the disposal steps they recommend for your area.
What are the symptoms and what should I do?
Symptoms can include blurred or double vision, drooping eyelids, slurred speech, trouble swallowing, muscle weakness and difficulty breathing. They can begin hours to days after eating contaminated food.
This is a medical emergency. Call emergency services or poison control right away, and tell them what was eaten. Keep the remaining food and the jar so the health department can test it, and let them know so others who ate it can be reached. A doctor or your local public health office is the authority here, not a guide like this one.
Key takeaways
- Botulism toxin cannot be seen, smelled or tasted, so a normal-looking jar proves nothing.
- Low-acid foods must be pressure canned using a current tested recipe.
- Never alter ingredients, jar sizes or methods in a tested recipe.
- When a jar looks or smells wrong, discard it safely without tasting.
- Seek emergency care immediately if symptoms appear after eating home-preserved food.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.