Can of soup with negative pressure (slightly implodes) on opening: Safe to eat?
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.
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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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