How do you know if a jar has botulism? (5 unmistakable signs)

In this article, we answer the following question: How do you know if a jar has botulism? We give you 5 unmistakable signs that something is wrong with the food that you are about to consume. We explain how botulism is produced and how to ensure the safety of your food.

How do you know if a jar has botulism?

There are five unmistakable signs that your jar has been potentially contaminated with Clostridium botulinum – the bacterium that produces botulism:

1.       Swollen/Bulging lid: If you realize that the lid of your jar is bulging or swollen, it may be a clear signal that there is contamination with Clostridium botulinum – one of the ten most dangerous foodborne pathogens (1) – or other anaerobic bacteria (spoilage organism) that is producing gas inside the jar. It is normal for a small depressurizing sound to be produced when you open canned food, but if it goes further, there may be a problem!

2.       Unusual texture: If you realize that there is a usual texture in your jar, such as being slimy, stringy, foamy or with bubbles, this could be a signal of the presence of bacteria inside (2). Bubbles generally indicate some type of fermentation, a bacterial process that is fine if intentional, but not if this process is not controlled!

3.       Foam presence and Cloudy liquid: foam is an indicator of bacterial activity (3). Clostridium botulinum and other harmful bacteria can survive, even spread, in environments with very little oxygen, such as canned foods (1). If you find that the liquid in your jar is cloudy or murky, this might indicate that it is contaminated with botulism.

4.       Strange odor: You should always check the odor of your jar to detect any strange odor that differs from its usual smell. If your jar smells sour, musty, or off in any way, it may be contaminated, and you should throw it away!

5.       Taste: The taste of your jar will change if it is contaminated with botulism. Check if the taste is strange, bitter, or metallic, those are clear signals or bacterial contamination (2, 4).

It is very important that you throw your jar away once you notice any of these signs.

Do not consume it! Botulism is a serious disease!

Take it seriously: The paralyzing botulinum neurotoxins that can be deadly (1), as will be explained in the next section.

What is botulism and what are the common causes of botulism in jars?

Botulism is a serious disease produced by the bacteria Clostridium botulinum (1). This microorganism can produce a potent neurotoxin (i.e., botulinum toxin) that can paralyze your muscles and can be fatal in severe cases (1).

If your jars were not properly canned or preserved, C. botulinum could grow and produce its neurotoxin as canned foods are ideal environments (low-acid, and low oxygen) for its proliferation (5).

Even if you canned your food by boiling or in a water bath at higher temperatures, the spores of the C.  botulinum can survive and begin to grow inside the jar, thus producing the fatal neurotoxin (6).

Botulism can develop in jars during the process of home canning. You must be careful when sterilizing your jars and during the food processing! Always keep an eye on the temperature and time during the processing to avoid bacterial contaminations (7-8).

Be sure that you are using the proper equipment to reduce the risk of botulism when preparing your jars. You should sterilize jars and lids and store them after preparation in a cool and dry place to avoid microbial growth. 

What are the dangers and symptoms of consuming jars contaminated with botulism?

The health risks of eating a jar contaminated with botulism are serious and it can be fatal (1)!

The neurotoxin produced by C. botulinum can cause paralysis of the muscles, especially those that control breathing, which can lead you to respiratory failure and even death (1).

Here you can find six clear symptoms of botulism (1). If you experience any of them after eating your food, you should seek medical attention immediately!

1.       Muscle weakness: As mentioned, the botulinum toxin can cause muscle weakness, starting in the face and spreading to the arms and legs.

2.       Fatigue: Botulism can also cause fatigue, dizziness, and general weakness.

3.       Difficulty swallowing: if you feel that there is something stuck in your throat, this could also be attributed to botulism as it can cause difficulty swallowing.

4.       Dry mouth: Botulism also affects your ability to produce saliva and can cause dry mouth.

5.       Blurred vision: A blurred vision, drooping eyelids, and double vision together with some of the previous symptoms is a clear sign for alertness.

6.       Paralysis: The botulinum toxin can (in severe cases) cause paralysis of your body muscles leading to respiratory failure and death.

It is important to keep an eye on the symptoms and seek prompt medical attention as treatment with antitoxin can greatly improve your chance of recovery (4).

What should you do if you suspect a jar of food has botulism??

You should take direct action if you suspect that one of your jars has botulism to reduce the risk of illness and to avoid spreading the toxin to other foods.

You should not consume the food inside the jar! Not even tasting it – it is now worth taking the risk– it could be fatal (1)!

You should isolate the jar and label it as contaminated. Also, you should check other jars that could also be contaminated, especially if you processed them at the same time or using the same method. Once you find one jar contaminated, it is possible that others are as well- be careful!

You should throw the contaminated jar away and especially the content in sealed and labeled bags. Do not reuse the jar for canning, some spores could still resist the cleaning process (6). If you are not sure how to proceed you can always ask your local health department for getting the proper handling instructions.

Remember botulism is a serious disease and you should take it seriously! 

How to eliminate Clostridium bacteria, their spores, and their toxins?

Bacteria and toxins are easy to eliminate following the proper sterilizing conditions (7,9). The problem is the spores, which are heat resistant, for that reason cooking or boiling food is not enough (6).

  • To be sure that food does not contain spores, it must be sterilized (subjected to temperatures of at least 116ºC, which is achieved in a pressure cooker or through industrial pasteurizations), subjected to high pressure, or irradiated. In most cases you will require special devices for this.

Be aware of disposing any contaminated jar, lid and its content in the proper way to avoid cross contamination!

Inform the local health authorities to be sure about the proper disposal protocols and ask for additional advice.

As always, the safety of the food we eat depends on the hygiene with which we handle it and that we apply good manufacturing practices.


In this article, we answered the following question: How do you know if a jar has botulism? We gave you 5 unmistakable signs that something is wrong with the food that you are about to consume. We explained how botulism is produced and how to ensure the safety of your food.


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