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I've always been told that if you see air bubbles in canned food, you should treat it like toxic waste. Today I opened a can of tomatoes and saw a few air bubbles form along the edges of the can. Is this what I was warned about? Or are they talking about food that looks like it's fizzing or oozing out of the can?

Here's a picture. There were ~2-3x that many bubbles when I first opened the can.

enter image description here

Notes:

  • I didn't notice whether there was a sound of air escaping when I opened the can. It was noisy in the room.
  • The can hadn't been extensively shaken or agitated before opening.
  • If it's hard to tell from the picture, that's enough of an answer for me. I just want to know whether this even remotely resembles what the "air bubbles" warning is talking about, or if it's totally unrelated.

3 Answers 3

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Octern,

It's a realative thing. What you're trying to determine is: where these gas bubbles generated out of something inside liquid portion of the can?

The reason that can be hard to determine is that many cans have a little air trapped in them. If the can has been agitated at all (doesn't need to be extensively), then you can get what look like bubbles coming from the tomatoes themselves, and it can be pretty hard to tell.

I generally look at it from a quantity/location standpoint: are the bubbles throughout the liquid, or are there only a few along one edge? In the end though, with tomatoes, I'd do what SAJ said. While they're probably OK, the penalty if they're not is pretty darned severe, and canned tomatoes are cheap.

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  • Definitely, they aren't an expensive ingredient. I've never seen air bubbles in canned tomatoes, and if I ever saw them I'd chuck them.
    – GdD
    Commented May 3, 2014 at 19:25
  • Thanks, this is what I suspected. I did try transferring the tomatoes to another container to see if there was more air trapped inside, and the results were... inconclusive. And yes, I'm not eating them.
    – octern
    Commented May 3, 2014 at 23:04
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I don't think many of us have actually seen bad canned tomatoes. It is exceedingly rare.

The risk versus reward ratio to save a bit of tomato which is not very expensive just isn't worth it.

Discard.

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  • That's surely the right choice in the absence of any better knowledge, but I'd still like to know if this is even the kind of thing the warning is talking about.
    – octern
    Commented May 3, 2014 at 18:24
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While everything that's already been stated in the existing answers are all good and wise, I do feel obligated to clarify some points:

  • Air bubbles may at times be present within the product and be totally safe for consumption. Unless the product is specifically vacuum sealed with the intent of eliminating all air pockets (which requires additional processing equipment and steps), it is not uncommon for air pockets to be present within the contents of the can; these are mostly sterile as they undergo lethality just as with the rest of the can's contents.
  • The presence of air bubbles themselves do not translate immediately to being hazardous; this is just my own inference (I worked in food safety for a frozen recipe meals manufacturing for a decade, nothing canned but I've glanced at a few HACCP plans for canned processing lines on occassion), but I believe the actual rationale behind air bubbles being a red flag is twofold:
  • We in the food safety industry generally utilize a mnemonic device to refer to the vital characteristics within a product that needs to be carefully measured and/or controlled in order to mitigate or reduce microbiological hazards: "FAT TOM". The "O" stands for oxygen, and the reason is that many (but not all) pathogens of concern require oxygen in order to proliferate. This isn't a set-in-stone fact for all of them, but it's one aspect that, when combined with many other criteria, helps us to facilitate safe and sanitary processing along with product shelf life that stays within spec. Do note, however, clostridium botulinum in particular is an anaerobic pathogen, meaning it does not require oxygen to proliferate. In the context of canned goods though, in the hypothetical event that a product were to be adulterated or contaminated with microbiological agents, there is a general tendency for them to release byproducts as they interact with the food, which then causes the creation of, e.g., carbon dioxide gas, etc. This process is what is known as fermentation, and it's said that these bubbles would be actively "moving" or "fizzing" when observed, rather than seemingly "inactive".
  • The presence of air bubbles may also be a concern due to the fact that it may represent a potential breech in the integrity of the container, which would then indicate a potential vector for contamination. However, most canned goods should come with a visual mechanism to indicate to the consumer if the product's seal is no longer intact.

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