Had a conversation with my wife today about the unopened mayo we had sitting in the pantry and it made me think – how does it make sense for a food (for instance mayo) to sit in a 65-70 degree pantry for months and be perfectly fine, but as soon as it’s opened it needs to be refrigerated. In my mind, if something needs to be refrigerated at any point, wouldn’t it always need to be refrigerated? The seal on the unopened product keeps the item safe, and the refrigerator does that when the seal is off? How do those two things relate?
In: 1789
Most people nailed pasteurization as the main thing that *generally* applies to foods that are “refrigerate after opening” and “button pops up when seal is broken”.
Mayonnaise specifically resists growing bacteria, but contamination, such as with a knife that might have had other things on it, can introduce *other* food for the bacteria to munch on, and mixing mayonnaise with other food can make the mayonnaise more edible for bacteria.
And as with many foods, letting it sit warm (such as out in the sun) *greatly speeds up* how much bacteria can reproduce, so that even foods like mayonnaise that resist bacteria could still end up hosting a lot of it with enough time. The reason refrigeration helps is that it keeps the temperature low enough that bacteria grow slowly, even if it’s contaminated.
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