eli5: How does food get bad even if it’s in a closed container that has never been opened?

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eli5: How does food get bad even if it’s in a closed container that has never been opened?

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It’s eaten away by fungi and bacteria that are present inside the packaging—unless it’s been cooked since it was sealed, such as if it’s been tinned. That’s why tinned food has a practically-unlimited shelf life.

It’s likely because of the non-sterilized cookware, container, or environment. To add, there are so many of bacteria in the air. The airtight container is not 100% oxygen free, so when the food is packed in an airtight container with bacteria in it, the bacteria will grow like there’s no tomorrow.

At some point, the container was open.

Things can get in it then from surfaces or the natural fauna microscopic organisms floating in the air.
So if the food has all of the bacteria and fungi on it killed, and then it is packed in a perfectly sterile environment, and delivered to the customer while keeping it away from any exposure to air, or anything non-sterile.. it’s possible to last quite a while…
This is canning.

This applies heat while the food is sealed. But you lose a lot of quality and texture since canning is essentially cooking it in the can It’s why things like canned tuna or green beans taste vastly different than their fresh counterparts.
Even then this isn’t perfect, some[ bacteria can survive the process if done improperly and grow well in an environment without air.](https://www.cdc.gov/foodsafety/communication/home-canning-and-botulism.html)

Also there is just a decline of quality. Sure chips or things of that nature can last a while if packed in specialized gasses but eventually some products oxidize or flavor compounds degrade. Technically safe to eat, but not preferred.