What Are the Signs of Botulism in Canned Food?

Botulism is a word that often sends people running to the hills in fear — so much so that many people steer clear of canning altogether because they’re afraid of poisoning themselves or their families. But a little knowledge can go a long way toward relieving those fears. 

The Botulism Myth

Most people don’t realize that Clostridium botulinum is a bacteria that’s all around us every day. It’s in the soil, in the water, and on the fruits and vegetables you eat. In its natural form, botulinum is pretty harmless, but it can produce a poisonous toxin under certain conditions:

  • Low acidity
  • Low oxygen
  • Moisture
  • Temperatures between 40°F and 120°F

It just so happens that these are all conditions home-canning provides. However, foodborne botulism is still quite rare

It’s understandable why home canning shoulders a lot of the blame for botulism, but the truth is that, on average, home canning is responsible for less than 10% of all botulism cases each year. It’s just that the few notable exceptions over the last 40 years have given home canning a reputation.

What most people don’t realize is that you can also get botulism poisoning from commercially canned foods.

Signs of Botulism in Canned Food

Proper canning techniques and knowing what to watch out for are your best defense against botulism. It’s one of the reasons you should remove the rings from your canning jars once they’re done processing. It’s also why you shouldn’t stack your jars. 

Should toxic spores remain in your home-canned goods, pressure will build and eventually pop the hermetic seal — the telltale sign that your food is no longer any good. If you see any kind of broken seal or bulging lid, toss your food. This goes for your commercially canned goods also. If you see any bulging in your store-bought cans, don’t risk it.

Before you open one of your home-canned jars, inspect the seal carefully to ensure the lid is securely fixed in place. If you can lift the entire jar by the lid, your seal is safely intact. If it slides or pops off, your seal is not secure, and you should dispose of your canned goods appropriately

As you begin to open your jar, if there is any hissing or release of air pressure, discard it. If the contents of your jar reveal any rising bubbles, if it appears cloudy or milky, if it is abnormally discolored, or if it appears foamy, toss it. 

Lastly, the nose knows. Smell the contents of your jar. If it has any foul odors or chemical smells, don’t eat it. 

Botulism spores are extremely resilient and can survive for years without revealing themselves, but they can produce a deadly toxin within a few short days in the right environment. You can’t see it or smell it, and you certainly can’t taste it. Although extremely rare, it is deadly. So, never taste-test your canned food as a way to check it’s still good.

In the vast majority of home-canning incidents, botulism occurs as a result of improper canning techniques, which is why it’s so important to stick with tested practices and recipes. 

How to Avoid Botulism

The best way to avoid botulism is to follow guidelines from the USDA or ag extensions. While botulism most often occurs with low acidic foods and pressure canning, using untested recipes with water bath canning also places you at risk.

Apply these best practices to avoid botulism:

  • Never alter the recipe ingredients or amounts since this could alter the pH levels of your food. 
  • Always use appropriate jars and lids.
  • Remove air bubbles before placing lids on jars.
  • Always maintain proper PSI and processing time.

While the fear of botulism associated with canning can be intimidating, as long as you’re following best practices, you really don’t have much to worry about.

Symptoms of Foodborne Botulism

Because botulism spores are toxic, they directly impact the nervous system. Symptoms can occur anywhere from four hours to eight days after consumption.

The first symptoms usually appear as vertigo mixed with fatigue and weakness, followed by blurred vision and difficulty speaking and swallowing. Sometimes abdominal swelling, constipation, diarrhea, and vomiting may occur, but not always. Gradually, symptoms progress to weakness in the neck, arms, and lower body, followed by the respiratory muscles.  

It’s absolutely essential that you know the signs of botulism in canned food and that if you suspect you’ve been infected with botulism, you seek emergency medical care right away. 

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