How to Tell When Your Canned Foods Become Spoiled?

C. Davis
By C. Davis February 16, 2015 12:34

How to Tell When Your Canned Foods Become Spoiled?

Have you ever opened a can you made a year before, and you didn’t know whether it was spoiled or not? Whether to throw it away or just remove – for example the mold – and consume the rest? I can’t even remember the number of times when I found myself in this situation.

For those of you who don’t know: Eating spoiled canned foods can result in death!!!

Especially bsmd_tr7y a bacterium called Clostridium Botulinum which in canned foods produces a toxin which causes botulism – a deadly form of food poisoning. In fact it is the most acutely lethal toxin known: only one teaspoonful is enough to kill 100,000 people. Improper home canning creates the perfect environment to grow botulism bacteria. Even if the chances are slim, the consequences are deadly. Please, feel free to share this information. You may save a life without even knowing it.

The botulism spores are heat-resistant and can survive in foods that are incorrectly processed, and are difficult to destroy. While high cooking temperatures will kill the bacteria, it takes even higher temperatures to kill the spores. That’s why the canning of low-acid foods is done with a pressure canner. If the spores are not killed in the canning process, they can become normal cells again and produce the deadly toxin.

Testing Jar Seals

test jarsMost two-piece lids will seal with a “pop” sound while they’re cooling, as the lid gets sucked down by the vacuum created by the contents cooling and contracting inside the jar. Usually spoilage produces gasses that cause the lids to swell and/or break the seal. So this is the first thing to check:

1. Press the middle of the lid with a finger or thumb. If the lid springs up when you release your finger, the lid is unsealed.

2. You can also tap the lid with the bottom of a teaspoon. A clear ringing sound means a good seal. If it makes a dull sound, the lid is not properly sealed. If food is in contact with the underside of the lid, it will also cause a dull sound (that is neither a problem nor a sign of spoilage).

3. Hold the jar at eye level and look across the lid. The lid should be concave (curved down slightly in the center). If center of the lid is either flat or bulging, it may not be sealed.

You should never eat food from a can with bulging ends. Bulging is one of several clues that might indicate contamination of food packaged in cans and jars.

Inspecting the Jar or Can (before opening it)

Bulges, dents near the ends of the can, a leak from anywhere in the can, a crack in the glass of the jar and RUST (for jars – rust on the margins of the lid) are reasons to toss out cans automatically. These can let air in and start bacteria to grow. Certain bacteria can cause what’s called “flat-sour” spoilage; basically the bacteria causes the food to become spoiled without creating any gas. So on the outside the can looks perfectly fine but inside, the food is spoiled.

Cloudiness – Dilemma (throw or eat?)

Cloudiness does not necessarily mean that the food has been spoiled. Cloudiness often accompanies flat sour spoilage, but you can detect a bad odor as well. Boil food 10 minutes before you taste it if the liquid is cloudy, or if you are unsure how the food was canned. If the food does not smell normal during boiling, throw it away without tasting. In spoiled foods, the cloudiness will usually be very obvious.

In certain foods, cloudiness may not indicate spoilage. For example, the starch content in over-mature peas and many kinds of dry beans can cause cloudiness. Uneven sizing of products can also cause cloudiness. For example, small tender peas will cook to pieces during heat processing, while more mature peas in the same can will keep their shape. The liquid will be somewhat cloudy under these circumstances.

In home-canned foods, hard water or salt containing impurities or additives, may cause cloudiness. In fruits, over-ripe fruit may make the syrup cloudy. Fermentation causes the liquid on brined dill pickles to become cloudy. In all of these examples, the cloudiness is normal and not harmful.

After and while Opening the Lid or the Can

For glass jars – a pop-top that does not pop when opened (loss of the vacuum) = a damaged seal – Throw away!

Mold – Dilemma (Scrape the moldy parts and eat what isn’t moldy? OR throw away everything?)

My mother always scraped the moldy parts that were over the jams and we ate the content. I had never had a problem. And I’m still doing that (with jams only).

BUT my mind tells me that the mold must’ve gotten in somehow, since all molds die in the boiling process.

And together with the mold it might have gotten in some serious bacteria that you simply cannot detect. So my advice to whoever asks is: Throw away!

I personally scrap the moldy parts only for jams – because it is not possible for jams to form Botulinum bacteria (almost all FRUITS have sufficient natural acidity to safeguard us against the risk of botulism).

In fact jams usually are so safe that June Taylor, who is a very distinguished preserver (in Berkeley, Calif.), says: “The only way that you can hurt someone with a jar of jam is if you crack them in the head with it.”

Smelling Dilemma

I’m sure there are a few people out there who – even seeing that the jar has mold – still smell it to see if it went bad. That is not a good idea because all the air surrounding the mold is full of spores; spores which inhaled may cause allergies and even some serious stuff in your lungs.

If the food doesn’t have any molds on the surface, smell it. If it’s spoiled … you’ll know it. I can’t tell you exactly the smell of a spoiled canned food, because it’s different from one jar to another – but it’s really bad.

Botulinum bacteria is one of the few which has no odor and can’t be seen, you can’t always tell which jars are tainted. The only things that you can check is proper sealing and swollen signs. If you suspect that a jar or can of food is spoiled, never, never taste it.

It’s really not much to say about the taste: if it has the taste it should: eat it. If not, throw it away.

simple 2Sometimes it’s tempting to take shortcuts, but when canning it’s not worth the risk. If spoilage microorganisms are not destroyed, canned goods are unsafe, and the consequences can be serious.


Is it safe to use jars or cans that have frozen accidentally?

Cans or jars that freeze accidentally, such as those left in a car or basement in sub-zero temperatures, can present health problems.

Because the food inside expands when frozen, the pressure inside the jar will rise. When this happens the lid might get air inside. Not very safe to eat!


Do crystals in canned goods mean the food is not safe?

Canned food (usually seafood) occasionally contains small fragments of a glass-like substance. According to the U.S. Food and Drug Administration (FDA), these crystals pose no danger to consumers. Known chemically as magnesium ammonium phosphate, commonly called “struvite,” the crystals can form from certain natural constituents of the fish or shellfish after they are commercially canned.


Can Pickles have Botulimia Bacteria?

Pickles are somewhat different because pickles work with vegetables, and vegetables are low-acid – which means they may develop Botulimia. But a pickle is a vegetable that has been covered with acidified brine, and that acid can either come from vinegar, that’s what we call a vinegar pickle or a quick pickle, or the acidity can be achieved through fermentation. That is to say, thanks to the wonderful processes of this micro-environment in which official lactobacillus bacteria are doing their thing, the fermentation process creates sufficient acidity to prevent the risk of botulism.


If I’m not sure about one… What if I boil the jar or the can before eating it, just to make sure?

No. That may help get rid of most harmful things, but not the worse one (botulimia). You can cook it out to kill the bacteria, but it’s not the bacteria that will kill you. It’s the toxin that it leaves behind.


What jars are best for canning?

It is important that you use heavy-duty jars made specifically for home canning.

“Mason” type jars, which screw shut with a threaded neck, are the most common choice. Do not re-use the lids, after a lid has been pried off once a perfect fit can no longer be guaranteed. The jars themselves can be used many times, as long as the rims are perfectly smooth and there are no scratches or cracks that would prevent a perfect seal.

Do not use commercial jars, such as empty peanut butter jars for home canning. Commercial jars are not strong enough to be safely used. Although most of the times – it works.


Is it safe to eat canned foods that went through a flooding?

Contaminated jars may be a problem following contact with water. Floodwater may contain sewage and animal wastes, oil, and other pollutants such as agricultural and industrial chemicals. After a flood, the Food and Drug Administration (FDA) recommends throwing away anything not stored in a waterproof container if there was a chance of contact.

BL_001_620x1002Resources and articles you may like:

How to Prepare for the Coming Food Crisis

What’s the #1 Killer In Any Crisis?

Do You Make These Fatal Mistakes In A Crisis?

30 Lost Ways of Survival from 1880 We Should all Learn

How To Prepare Medicinal Pickled Garlic

5 Home Remedies for Diarrhea

Home Food Safety Information

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C. Davis
By C. Davis February 16, 2015 12:34
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26 Comments

  1. Stardust February 20, 19:47

    Thanks for the warnings. They came in useful for me.

    I use the small plastic peanut butter jars for freezing leftover jams when I have no more glass jars. I clean them with hot soapy water first. Leaving a 1/2 inch at the top allows it to freeze and move without exploding the lid. I often have to do this when I under estimate making jelly and jam recipes. When my friends and family want all that I have canned, I can reap my reward by thawing out my freezer jelly leftovers,

    Reply to this comment
  2. Grandma March 7, 16:02

    You lost me in your opening paragraph:
    ” Have you ever opened a can you made a year before, and you didn’t know whether it was spoiled or not? Whether to throw it away or just remove – for example the mold – and consume the rest? I can’t even remember the number of times when I found myself in this situation.”
    Why would I follow the advice of anyone whose canned food has ever been moldy even once, let alone one who can’t even count the number of times it was moldy?

    Reply to this comment
    • C. Davis Author March 9, 16:52

      Congratulation for your “unspoilable” cans. You should read this advice EXACTLY because my cans go bad from time to time. I’m alive and well.

      Reply to this comment
  3. Mom of Elizabeth March 24, 14:07

    I took a microbiology class at my jr. college. My teacher always had a story to open the lecture. One story she told was the time she had to figure out why a whole family was dead sitting around the dinner table. Found out that they ate the pickles that were canned and they died of botulism. So yes pickles can kill if not canned properly.

    Reply to this comment
    • Bear June 18, 03:01

      Sorry, but it would NOT affect them THAT quickly!!!
      “The symptoms of botulism depend upon the age of the person exposed. In adults this may include difficulty in swallowing, speech, and breathing, and double vision. The onset of botulism is usually 18 to 36 hours after eating the contaminated food, although it can be as soon as four hours and as long as eight days. In infants, signs of botulism include constipation, muscle weakness, and loss of head control, also called “the floppy baby.””

      Reply to this comment
  4. suzie queue June 9, 18:25

    Want to share my experience of canning and putting up for the last 45 years.

    1. If you can have only one canner – get a pressure canner. You can use it as a water bath any time by not using the weight.

    2. You CAN use certain commercial jars for reuse in home canning. I learned this in the 1970’s from either Mother Earth News or Organic Gardening and Farming magazines. I have been doing it ever since and have not had any issues of spoilage. You can ONLY use the jars that come with a lid with the rubber seal inside the lid. You boil the lid to soften the seal then tighten both before and after canning. That is the ONLY time you re-tighten a jar lid. The glass jars in other types of canned goods, such as mayonnaise jars are not suitable even with a mason-type canning lid. The glass is too thin to survive the pressure canner. I reuse glass pickle jars and spaghetti jars the most. They are the best.

    3. Also, regarding the canning of fats. I use a pressure canner to can meat drippings, just as if I were canning meat. I don’t take any chances. Also, I have bottled butter the same way. When you can or bottle butter, you melt it first then dip the melted butter in the jars with a ladle. When the canning process is over, as the jars are lukewarm and the butter is thickening back up you will need to turn the jars several times to remix the butter with residual milk that separates out during the canning process. All my canned butter has a little bit of milk in the bottom where not all the milk will reassemble. It won’t change the taste or hurt anything. The texture of the butter is a little different, but tastes great.

    4. Canning Safety: Do not turn HOT jars, fresh out of the canner EVER. The sudden shift of hot air which is between the food and the lid will expand and the jar will BLOW UP. When I first learned to can, I was told by someone to turn the jars upside down to “sterilize the inside of the lid”. WRONG!!! Everything gets sterilized during the canning process. So, I turned a hot jar upside down and BOOM, jar exploded and hot food scaled me everywhere. DON”T DO IT.

    Reply to this comment
    • Lou September 9, 04:26

      I remember that my grandmother canned chicken and pork by seasoning and flouring it, then frying before she put it into jars. She did not cover it with water she just canned it in a pressure canner for what seemed like forever to a young child. I can close my eyes and see those wonderful meats sitting on the pantry shelf with about an inch of fat in the bottom of the jar. They were so good and oh so tender. Does anyone know how meat like that was canned about 65 and earlier years ago. I am now 75 but still remember her pantry clearly. I would like to be able to copy what ladies did then. Can anyone help? She lived in the Florida Panhandle as I do.

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