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When Good Preserves Go Bad

Determining the Safety of Canned Foods -

Just like planning next year’s garden – This is the time of year when I start to think about next year’s canning season.

For me, part of that process is going through all the cupboards to dig out any of last year’s leftover preserves.

It is time to see:

  • How many jars are left to eat?
  • What did I make too much of? {I went a little plum crazy last year}
  • Are there any jars that need to be thrown out?

That last one is an important topic because sometimes good preserves go bad.

Assessing the safety of your canned goods is important to do every time you open a new jar.

But what exactly should you be looking for?

Well, here’s the scoop…

Common Sense:

As you look at the list below, you might be thinking, “Well many of these tips are common sense“.

That is so true.

But I have found that when it comes to homemade preserves, many people can totally lose their common sense. Ha!

Perhaps it is because we have put so much work into creating those preserves. Or maybe it is because in general, canners are a frugal bunch who hate waste.

But for whatever reason, for every sign of spoilage listed below I have had someone ask me if they could still eat the contents of those jars.

And they ask this with pleading eyes – hoping beyond hope that I will say yes. But I tell them no.

Don’t do it.

Don’t eat anything that is questionable. It’s not worth it.

Also, a Reminder:

You should always store your jars with the rings OFF. You’ll see why as your read below or you can go to this post on Why Remove Canning Rings to learn more.

Remove Canning Jar Ring -


7 Signs of Spoilage (Plus Tips):

1) An Unsealed Jar:

This is the most common scenario: You reach for a jar of preserves and the lid just falls off.

It’s not sealed.

If you just processed that jar (in the last 24 hours), you could reprocess it or refrigerate it and it would be okay.

But if it has been on the shelf for weeks or even months, you have no choice but to chuck it. You have no idea how long it has been open or more importantly…why.

Throw it out.

2) A Weird Smell:

If you ever open a jar of homemade preserves and it just smells off, rancid, or just plain “bad”, throw it out.

The rule of thumb is that if it smells bad, it IS bad.

Please, don’t taste it to be sure.

Just throw it out.

3) Mold:

If you find mold on the contents in the jar or on the lid of the jar, you need to throw the food out.

Yes, our grandparents would simply scrape off the “bad” parts and eat the rest. But here’s why I don’t recommend that:

First, we now know that mold grows with long tentacles that reach down into the food. Scraping off the top only removes the part you see. You may not be removing all the mold and some molds are carcinogenic.

Also, mold can change the pH of the food. If it has changed enough, you could have something much more dangerous than mold growing in there.

Throw it out.

4) A Funky or Slimy Texture:

Any time you open a jar and the texture of the contents is not as you expect, it can be a sign of spoilage.

Now, I am not talking about something just having a slightly softer texture than it had when fresh. All canned food will soften a bit during the canning process. This is because the canning process cooks it slightly.

But if you open a jar and the food is slimy and slippery or the texture is disintegrating, you need to toss out the food.

5) Bubbles Actively Rising in the Jar:

If you see bubbles moving inside the jar, it is a sign of bacterial activity and fermentation. Since you don’t know exactly what type of activity is happening, you need to throw it out.

If you have stored your jars without the rings (as you should), the jar will unseal (see #1 above) and you may never have to search for bubbles.

That is just another reason not to store jars with the rings on. Doing so allows you to know right away if something is happening inside that jar.

Note: This bubble thing can throw off new canners because there is one time when it IS okay to see a bubble move – and that is when you first process the jars.

You see, immediately after processing and for about 48 hours after, bubbles inside the jar can dislodge and rise to the top as the food cools and settles.

That is normal.

But if you see bubbles moving after a jar has been on the shelf (unmoved) for weeks/months, something else is going on in there and you need to throw it out.

6) A Bulging or Leaking Lid:

Again, this only happens if you have stored the jars with the rings on and bacteria activity builds up pressure inside the jar.

Look, you should never have pressure build up inside the jar. Instead, that jar should be under vacuum (the opposite of pressure).

So a bulging lid is a sign of spoilage.

Throw it out.

And next time, store the jars without the rings. (I won’t stop harping on that one…tee hee)

7) Spurting Liquid When Opened:

This too would only happen if you left on the rings and bacteria activity raised the pressure inside the jar.

Any jar that spurts out the contents when you open it should be thrown away as this means spoilage.

Signs of Spoilage in Canning -

Final Important Tips:

  • Don’t taste anything to “test” it. It is not worth it.
  • Even if the contents are bad, you can save the jars. Just wash them thoroughly.
  • Remember to discard the used lids. They can only be used once anyway.
  • Store all your canned goods without the rings.
  • The USDA has very stringent clean up instructions if you suspect you have a jar with botulism inside. The process is called detoxification and is pretty extensive. You can go here to read on that.

My goal is to empower you with knowledge so that you have no fears. Canning season is coming soon!

So tell me…

Does this make you feel more nervous or more informed? Tell me in the comments!

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About the Author:

Theresa Loe is the founder of Living Homegrown® and the Canning Academy® and is the Co-Executive Producer & Canning Expert on the national PBS gardening series, Growing A Greener World®. Theresa homesteads on just 1/10th of an acre in Los Angeles with her husband, two teenage boys and several disorderly but totally adorable chickens. Learn more about Living Homegrown here and about the Canning Academy here.