Eli5: What happens to a food product when it expires?

Question

And how do you tell an expiry date

In: 1

Answer 1

You tell by testing it, then adding some margin of error. What happens depends a lot on the product. Milk goes sour, bread goes stale, vegetables wilt or rot, harmful bacteria multiply, or a host of other bad things. Or maybe the ingredients just separate. The white “bloom” on old chocolate is sugar migrating to the surface, but it’s still perfectly edible.