Opened a can of soup and it made a loud noise with the open-tab lid suddenly pulling in.

I know that bacterial decay can make cans bulge (due to gaseous byproducts of bacterial metabolism) and the general rule is that bulging cans or cans that expel a large amount of gas on opening should be discarded.

However, are there any known dangers associated with negative pressure in a can that implodes enough to pull the can lid in on opening? There are relatively few types of bacteria that consume gases (an example being nitrogen-fixing bacteria in legumes).

The can wasn't visibly deformed or damaged in any way before or after opening.

  • I would tend to disagree that this would be more suited to Physics SE. In particular, the question is: "Are there any known harmful/dangerous bacteria that would cause this behavior?" which definitely is on-topic. Nov 6, 2017 at 20:57
  • 1
    Well, the answer to it is no, because the negative pressure is not due to bacteria but standardised sealing processes (the sterilisation of the food is usually achieved with vacuum sealing of the can). Hence the negative pressure. Any questions regarding the negative pressure are better suited for Physics.SE. This is what I meant.
    – Narusan
    Nov 6, 2017 at 21:02
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    Thanks. Go ahead and that as an answer, I will upvote and accept it. Nov 6, 2017 at 21:03
  • Deleted my off-topic comment by the way, my answer is - at least in my understanding of the site’s scope - perfectly on-topic. I thought you’d want to inquire sealing and sterilisation techniques and why there was a negative pressure exactly, which would not be best suited here. As it is, the question is perfectly fine.
    – Narusan
    Nov 6, 2017 at 21:24

1 Answer 1


One method of food sterilisation involves vacuum-sealing. This is why there was negative pressure in the can1 and why the lid got sucked in as soon as it was able to move.

Bacteria creating positive pressure is due to digestion and excretion of gasses, which have a lower density and thus result in higher pressure. I am unaware of any bacteria or other germs that will excrete substances significantly condensed so that a negative pressure will result.

1: Ironically, what made you think the product might be spoiled is what ensured the product wouldn’t get spoiled.

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