Food Safety Guide

Botulism in Canned Food: Signs, Symptoms, and Why Looking Is Not Enough

You cannot see, smell, or taste botulism in canned food. Whether a jar is safe was decided months earlier. It comes down to the conditions it was canned under, not anything you can check today with your eyes or your nose.

This guide covers what actually decides the risk. It covers the warning signs food scientists do rely on, and what to do with a suspect jar. It also covers when symptoms mean you need emergency care right now.

Last updated: August 28, 2026 · Sourced from the CDC, USDA, USDA FSIS, and the National Center for Home Food Preservation

The One Fact That Matters Most

Botulinum toxin does not change how food looks, smells, or tastes. The CDC states this plainly: “You cannot see, smell, or taste the toxin that causes botulism. But taking even a small taste of food containing the toxin can be deadly.” (CDC)

That fact changes how you have to think about this. You cannot inspect your way to safety. A jar that looks perfect can still be dangerous. A jar with a bulging lid usually is dangerous, and we cover signs like that below. But a normal-looking jar is not proof of anything.

The warning signs later in this guide are real and worth checking. Their presence is always a reason to throw food out. Their absence is never a reason to eat it.

Why Low-Acid Food Needs a Pressure Canner

Clostridium botulinum is a bacterium that lives in soil almost everywhere, including your garden. In open air, it is harmless.

The bacteria protect themselves with spores, a tough coating that can survive for years. Canning creates the exact conditions those spores need to wake up and grow: no oxygen, low acid, some moisture, and a temperature they can tolerate. A sealed jar is airtight by design. That is what makes canning work as food storage. It is also what makes it risky if a step gets skipped.

Plain boiling water reaches 212°F at sea level. That kills most bacteria, but it does not destroy C. botulinum spores. Inside a sealed, low-acid jar, any spore that survives can wake up and grow, and as it grows it produces the toxin. This can happen with no gas, no smell, and nothing visible on the outside of the jar. USDA’s Food Safety and Inspection Service explains the same mechanism. A low-acid food canned without enough heat leaves the bacteria alive as spores. The sealed jar then gives those spores exactly what they need: no oxygen. They wake up and make toxin, right at room temperature. (USDA FSIS)

A pressure canner solves this because it runs hotter. At 10 to 15 pounds of pressure, the water inside reaches 240°F to 250°F. The National Center for Home Food Preservation says destroying those spores takes between 20 and 100 minutes at that heat. The exact time depends on the food, the jar size, and how it is packed. (NCHFP) A boiling water canner cannot reach that temperature no matter how long you run it. That is the entire reason pressure canners exist.

The pH 4.6 Line: Which Foods Need Pressure Canning

Whether a food needs a pressure canner comes down to one number: pH 4.6. Below that line, food is acid enough to stop C. botulinum from growing, even if a spore survives processing. Above it, a boiling water canner is not a safe option, no matter how long you process the jar. (NCHFP)

Food type	pH	Safe canning method	Examples
Acid food	4.6 or lower	Boiling water canner	Most fruits, pickles, sauerkraut, jams, jellies, fruit butters, properly acidified tomatoes and figs
Low-acid food	Above 4.6	Pressure canner only	All fresh vegetables (except most tomatoes), red meat, poultry, seafood, milk, and most mixed foods like soups and chilis

Tomatoes are the food that trips people up. Home canners have treated them as an acid food for generations, and most still qualify. But some modern varieties, bred to taste sweeter, sit at or slightly above the pH 4.6 line, and the same is true of figs. (NCHFP) You cannot test your own tomatoes at home. So USDA guidance calls for adding bottled lemon juice or citric acid to every jar of home-canned tomatoes and tomato products. Do this every time, with every variety, no matter how ripe they are. This is not optional caution. It is the only way to guarantee the acid level lands where it needs to be.

What Raises Your Risk

Most home-canning botulism cases trace back to one of these problems. Any single one is enough to matter.

An untested recipe. The CDC is specific here. Use only recipes and cookbooks that follow the USDA guide. And do not substitute one, “even if you got them from a trusted friend or family member.” (CDC) A recipe that was never lab-tested has no known safe processing time.
Boiling-water canning a low-acid food. Green beans, corn, and meat processed in a boiling water canner never reach a spore-killing temperature. Low-acid vegetables are the most common source of home-canning botulism outbreaks in the United States. (CDC)
A jar that never sealed, or lost its seal. A concave, tight lid means the vacuum seal held. A flat or bulging lid means air got in, and the risk went up with it.
Skipping the altitude adjustment. Water boils at a lower temperature the higher up you are. Above 1,000 feet, both the pressure and the time in a USDA recipe need to go up. The same process that works at sea level will fall short at your house.
Garlic or herbs stored in oil. Oil seals out air the same way a canning jar does. The CDC lists chopped garlic in oil among the newer sources of botulism cases. (CDC) Refrigerate any homemade infused oil, and throw out what is left after four days.
Home fermenting or curing without a tested process. In Alaska, most foodborne botulism cases come from traditionally fermented fish and other aquatic animals. (CDC) The same low-oxygen conditions apply to any home fermentation project that skips a tested method.

Warning Signs, and What They Do Not Prove

These are the signs the CDC and USDA say to check for, before you open a jar and again as you open it.

The lid or container is bulging, swollen, or leaking
The container looks cracked, damaged, or just not right
Liquid or foam spurts out when you open it
The food is discolored, or has mold on top or on the underside of the lid
It smells wrong in any way

(CDC) Any single one of these means the food gets thrown out. Do not taste it first, not even a small amount, to check.

Now the harder part. The National Center for Home Food Preservation is direct about this. Spoiled low-acid food, tomatoes included, “may exhibit different kinds of spoilage evidence or very little evidence” at all. (NCHFP) That is why extension offices give the same advice every time. Treat any suspect low-acid jar as contaminated. It does not matter whether it shows a single sign on this list. An untested recipe does not get cleared just because the jar looked, smelled, and felt normal. Neither does a missed altitude adjustment. Neither does the wrong canner used on the wrong food.

If You Find a Suspect Jar: Detox and Disposal

Do not just pour a suspect jar down the sink or toss it in the trash as it is. The food and the container can carry enough toxin to hurt a person or an animal handling the trash later. That is why USDA’s Complete Guide to Home Canning lays out a specific process. (NCHFP)

First, check whether the container is still sealed shut.

Still sealed, just swollen or bulging

Double-bag the can or jar in a heavy trash bag. Put it straight into the regular trash, or dispose of it at a landfill.

Unsealed, already open, or leaking

It needs to be detoxified before it goes anywhere near the trash. Use the steps below.

The detoxification process

Put on disposable rubber or heavy plastic gloves before you touch anything.
Lay the containers and lids on their sides in a large pot, at least 8 quarts, such as a stockpot or your boiling water canner.
Cover them completely with water, with at least 1 inch of water above the containers.
Put a lid on the pot, bring it to a full boil, and boil for 30 minutes straight. This step is what destroys the toxin.
Let everything cool, then throw the containers, lids, and food away in the regular trash or at a landfill.

Botulinum toxin can be dangerous through a cut or opening in the skin, not just by mouth. So treat any surface the food or its liquid touched the same way you treat the food itself. Mix 1 part unscented household chlorine bleach with 5 parts water. Spray or wipe it on counters, tools, can openers, anything that made contact, and let it sit for 30 minutes. Wipe it up with paper towels, and bag those before they go in the trash. Apply the bleach solution a second time, let it sit another 30 minutes, and rinse. Wash your hands and any reusable items afterward, and only then take the gloves off. (NCHFP)

Symptoms and When to Get Help

Foodborne botulism does not usually show up right away. USDA’s Food Safety and Inspection Service says symptoms typically start 12 to 36 hours after eating contaminated food. Documented cases range from 4 hours to 8 days. The sooner symptoms start, the more serious the case tends to be. (USDA FSIS)

Watch for:

Trouble swallowing
Muscle weakness
Double or blurry vision
Drooping eyelids
Slurred speech
Trouble breathing
Trouble moving your eyes

Foodborne botulism often adds nausea, vomiting, or stomach pain early on, before these nerve symptoms start. Not everyone gets every symptom at the same time. (CDC)

Botulism is a medical emergency. If you or your child has any of these symptoms, especially after eating home-canned food, go to the emergency room right away. Do not wait to see if it passes. (CDC)

Doctors treat botulism with an antitoxin. It works best when given early. It stops toxin still in the blood from doing more harm, but it cannot undo damage the toxin already caused. Some patients need a ventilator while their breathing muscles recover, and recovery can take weeks or months. With modern antitoxin and hospital care, fewer than 5 out of every 100 people with botulism die. (CDC) That number depends on getting care fast.

Infant Botulism and Honey

Infant botulism works differently from the foodborne kind, and it looks different too. Instead of eating toxin directly, a baby swallows spores, and the spores grow inside the baby’s gut. Watch for constipation, poor feeding, a weak or different cry, drooping eyelids, and a face with less movement than normal. (CDC) These signs are a reason to see a doctor right away, the same as the adult symptoms above.

Most cases of infant botulism have no clear, preventable cause. The spores live in soil and dust, and they turn up on floors and counters even in clean homes. (CDC) But there is one real exception, and it matters for a homesteading kitchen: honey can carry these spores. The CDC is clear that no child under 1 year old should have honey in any form, including honey pacifiers and foods baked with honey. (CDC) After a baby turns 1, an adult gut handles the spores without a problem. Before that, it is a real risk with a simple fix: no honey.

The Boiling Step, and What It Does Not Do

The CDC recommends boiling home canned vegetables and other low acid foods for 10 minutes before you eat them, adding one minute for every 1,000 feet you live above 1,000 feet. (CDC) Boiling destroys the toxin. It is worth doing.

This is not a way to rescue a jar you doubt. Boiling breaks down the toxin, but it does not destroy the spores that made it, and it does not fix a jar that was canned the wrong way. It is a last layer of protection on food you already believe was processed correctly. A jar you have any doubt about does not get boiled and eaten. It gets the disposal steps above.

Think of it the way you think of a seatbelt. You wear one expecting not to need it. You do not use one as a reason to drive badly.

What Not to Do

Do not taste, smell, or otherwise test food to decide if it is safe. The toxin does not announce itself, and a small taste can be fatal.
Do not assume a normal-looking jar is safe just because nothing seems wrong. As covered above, spoiled low-acid food can look completely normal.
Do not try to fix a suspect jar by reboiling it, reprocessing it, or re-canning the food. There is no home step that makes contaminated food safe to eat. Discard it using the process above instead.
Do not feed a suspect jar to a dog, chickens, or any other animal instead of throwing it away. The toxin is dangerous to animals too, not only people.
Do not use a boiling water canner for a low-acid food because a recipe looks similar to one that calls for it. Looking similar is not the same as being tested.
Do not can from a family recipe, a blog post, or an old recipe card unless it matches a tested USDA or extension source. “It has always worked before” is not the same as “it was tested.”

Where This Fits

If pressure canning is new to you, start with our guide to choosing a pressure canner, which walks through size, material, and gauge type. Deciding between the two most common models? Our All American vs Presto comparison covers price and long-term durability.

High-acid foods like pickles and jam do not need any of this. Our best water bath canner guide covers the right equipment for that side of canning. Building a full setup from nothing? Our canning supplies guide lists jars, lids, and tools in one place.

For every guide we publish on canning, dehydrating, and other food preservation methods, see our food preservation hub.

Common questions

Can I taste a small bit of canned food to check if it is safe?

No. Never taste food to test it. Botulinum toxin does not change how food tastes, and a small amount can be deadly. If you have any doubt about a jar, throw it out using the disposal steps in this guide instead of tasting it.

Can I use a boiling water canner for green beans or other vegetables?

No. Vegetables are a low-acid food. A boiling water canner only reaches 212°F, and that is not hot enough to destroy Clostridium botulinum spores. Only a pressure canner reaches the 240°F to 250°F needed. Using a boiling water canner on a low-acid food is one of the most common causes of home-canning botulism in the United States.

Do I really need to add lemon juice to home-canned tomatoes?

Yes, every time. Many modern tomato varieties sit close to, or just above, the pH 4.6 safety line. You cannot judge this by taste or by variety name. USDA guidance calls for adding bottled lemon juice or citric acid to every jar of home-canned tomatoes, no exceptions.

My jar has no bulge and smells normal. Is it safe?

Not automatically. Spoiled low-acid food can show little or no visible sign of a problem, according to the National Center for Home Food Preservation. A normal-looking jar is not proof of safety if you have doubts about how it was canned, such as an untested recipe or a skipped altitude adjustment.

Is it safe to feed a suspect jar to my dog or chickens instead of throwing it away?

No. Botulinum toxin is dangerous to animals, not just people. Treat a suspect jar the same way no matter who might eat it. Dispose of it using the detoxification process in this guide, not the compost pile and not the pet bowl.

Can honey cause botulism in my baby?

Yes. Honey can carry the spores that cause infant botulism, including in baked goods and honey pacifiers. The CDC says no honey in any form for a child younger than 1 year old. After age 1, it is not a concern.

How soon do botulism symptoms show up after eating contaminated food?

Typically 12 to 36 hours, though documented cases range from 4 hours to 8 days, according to USDA’s Food Safety and Inspection Service. Watch for trouble swallowing, blurred or double vision, drooping eyelids, slurred speech, and trouble breathing. This is a medical emergency. Get care right away. Do not wait to see if it passes.