Canned goods can help you pad your pantry to be ready for tough times or just speed up meal prep. They really are great, and one of the best and most reliable ways to preserve food.
But whether you buy them from the grocery store or can them yourself at home, the process isn’t infallible and whatever kind of food you have, it won’t last forever. Just like everything else, canned food can spoil, and sometimes with disastrous results.
It’s often gross, yes, but sometimes canned food can spoil and give only the subtlest outward sign.
Nonetheless, eating it might make you terribly ill, or potentially even kill you! That’s why you’ve got to pay attention and constantly be on the lookout for signs of spoilage in your canned goods.
Keep reading and I’ll give you some sure signs to watch for.
A Badly Dented or Rusty Can
If you have store-bought canned goods at home, do an inventory and get rid of any that have a badly dented or obviously rusty can.
You might think it’s okay, and though small, shallow dents are usually nothing to worry about, major dents are highly likely to compromise the seal of the can, or sometimes break off part of the liner, which can allow unwanted chemical reactions to take place.
Similarly, a badly rusted can is also a warning sign, particularly if the rust is thick and located around the rim, on the top, or the bottom.
It might be tempting to open the can and see what’s inside, but even with fresher goods, you’re probably in for a rude surprise. Just don’t risk it, and pay attention to the cans you’re getting at the grocery store to avoid bringing one of these home!
Bulging Lids
A major warning sign with store-bought or home-canned goods, and one that most of us have had the misfortune of encountering before, is a bulging lid.
Such a is always indicative of one thing: spiking pressure inside the can. But how does that happen, and what makes the lid bulge?
It’s disgusting, but once bacteria start to form inside the can and start digesting the contents, they release gas. Yep, that gas pressure is basically the microscopic farts of millions of tiny little organisms.
As the bacteria do their work, the pressure grows and grows until one of two things happens: the material of the can fails and it bursts open, or you foolishly open it yourself. Then you’ll have an eruption!
If you notice a metal can starting to balloon around the midsection or either end, get rid of it. The same goes for a mason jar that has a puffy lid.
Noticeable Fizzing or Bubbles
For glass jars, carefully inspect the contents in good lighting, looking for any bubbles when the contents are at rest. Note that if you shake or jostle the jar, it’s likely that some bubbles will form, but this isn’t what I’m talking about…
Be on the lookout for something that looks a little bit like the foam or fizz you’d see on a carbonated drink.
If you see these little bubbles around the perimeter or congregating up near the neck of the jar, it has certainly gone bad: it’s the gas released from bacteria again!
Even if the food looks fine otherwise, you simply cannot risk it. Throw the whole thing out.
Squirting Liquid Upon Opening
Carrying on with gas pressure buildup inside the can or jar, sometimes enough will form to cause a noticeable squirting or small eruption once you crack the seal or remove the lid, but it won’t bulge or deform the can otherwise.
Opening any jar, store-bought or home-packed, shouldn’t be like cracking open a can of biscuits. We don’t want a big pop!
When you first crack open the lid of a metal can with your can opener, watch for liquid to squirt out. The same thing goes for popping open a glass jar.
A little bit of liquid overflowing isn’t anything to worry about, but if it comes out under pressure, that is a no-go.
Leaking
This one is easy, obvious, and an instant qualifier for a trip to the garbage can: any jar or can that has obvious leaks around it, or dried residue on the outside, cannot under any circumstances be trusted.
Throw it away. That invariably tells you that the seal was compromised at some point.
Do note, though, that there are some common sense exceptions here: if you are canning at home and get a little sticky residue from your hands or a tool on the outside of a jar, the contents could be just fine.
This is one reason why we always thoroughly wipe down and clean jar exteriors before we store them. You don’t want a false positive!
Another possible exemption is if there was an accident or spill that splashed on the outside of a jar or can.
Again, the contents could be perfectly safe and you’re looking at a false positive. But if you do not know, for sure, that either one of these eventualities did in fact take place, you simply cannot risk it!
Bad Seal
Home canning lids and many varieties of grocery store canned goods use safety lids that will inform you at a glance of whether or not the seal is intact.
These button tops, as they are sometimes called, have a little divot that should be flat and inflexible when the seal is intact.
When the seal is broken, they pop up and can be pressed, visibly moving and often producing a popping sound.
When you can your own, are picking up groceries, or bringing either out of storage, check the top: it should be flat and unmoving, and when you pull the lid off, there should be an audible hiss and pop as the pressure is relieved.
As long as the pop top is still intact, chances are overwhelmingly in your favor that the contents are still safe and sound.
Cracked Jar
For home-canners or anyone who gets home-canned goods from family and friends, look over those jars really closely for cracks. This can be a sneaky one!
It is possible that a jar cracks after canning from rough handling or simply from degradation over time. Other reasons include forgetting to preheat it before canning, touching jars inside the canner, or not using a canning rack in your water bath (the bottom of the jar will be in full contact with the button of the pot in this case).
It’s also possible that a cracked jar might, at first glance, hold food and then be successfully sealed. But it rarely fails that a cracked jar will facilitate spoilage.
Just like a badly dented can we talked about up above, you simply must not trust a cracked jar no matter what.
And another thing: even if you accidentally cracked it yourself right before you go to pour the contents, do you really want to risk there being a sliver of glass in your food? No, you don’t. Throw it out!
Foul or “Off” Odors
Another really obvious sign, and one that I trust nobody reading this will ignore! When canned food smells off, or just really bad, you’ve got a serious problem. There’s no two ways about it: your food has spoiled.
Doesn’t matter how new it is, doesn’t matter how it looks, doesn’t matter how it was stored: it has gone bad, and you shouldn’t eat it even if you’re starving.
Altered Texture
This can be a subtle one that you might not notice until it’s too late and you’ve taken a bite. Sometimes canned food can look entirely normal, smell normal, and appear for all intents and purposes… normal.
However, when you start to spoon it out, cut it, process it, or heat it up, you notice that texturally it’s not quite right. Maybe it seems too mushy. Maybe it’s a little grainy. Sometimes it’s hard to put your finger on it, but you know it when you encounter it.
Often, this can indicate spoilage, but not always: you might have food that is still safe and edible, but it’s been in storage so long that it has naturally just degraded somewhat.
You can make a judgment call here, but you already know what I will tell you to do: get rid of it!
Discoloration
This is another potential warning sign, but not a guarantee of spoilage. Food that has taken on a strange color, usually a darkening, could be spoiled. However, many foods will naturally discolor over time when canned. Fruits and stone fruits particularly are notorious for this.
Similarly, canned food that is kept in a warmer environment will often discolor more than that kept in a cooler environment. Warmer temperatures facilitate rapid spoilage, but it doesn’t mean the food has gone bad.
Use your head and all of your senses in this case: if the food was recently canned and is showing no other signs of spoilage, it’s probably okay. But once again, it might not be worth the risk!
Heinous bacteria, like the infamous Clostridium botulinum, which is responsible for causing potentially deadly botulism from toxins it produces, can inhabit food that does not smell, taste, or look any different…
Visible Mold or Slime
The biggest red flag of them all, perhaps second only to a bad odor. Any canned food that has visible mold or slime growing on it should be trashed at once and with extreme prejudice.
Don’t even think about trying to pick out the bad pieces or cut off bad parts: contamination is already total. Also, don’t play amateur biologist and try to figure out what the mold is and whether or not it is actually dangerous.
Many common molds and other microorganisms associated with food spoilage—Aspergillus, Citrimyces, and Penicillium foremost among them—can make you horribly ill and even cause death if you’re already suffering from health complications.
Strange Flavor
Remember when I told you to use all of your senses? Assuming your food looks perfect, smells perfect, has a perfect texture, and came out of a perfectly intact can or jar, you still shouldn’t trust it if it tastes a little off.
This is another “know it when you see it” factor, or I guess I should say, “know it when you taste it!” If the food tastes slightly foul, bitter, metallic, rancid, or just peculiar, that is telling you that something has gone wrong with it.
Canned food should taste exactly like what it is, and it should taste fresh and good! If it doesn’t, not only is it not worth it, but it might be dangerous. Ditch it.
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Tom has lived and worked on farms and homesteads from the Carolinas to Kentucky and beyond. He is passionate about helping people prepare for tough times by embracing lifestyles of self-sufficiency.