We know that you can heat bacteria to death but freezing them just preserves them.
Why doesn’t freezing cause water to expand and rupture their cellular structure? Or at least cause their life-preserving processes to halt? Why don’t they need heat to live the same way as macro-animals?
An extension to this theme: Bacteria (over the millennia) have experienced many freeze-thaw cycles and have subsequently evolved survival techniques. Conversely, they probably have experienced few thaw-boiling cycles, hence their vulnerability to extreme heat?
Right. There ARE bacteria that can survive boiling water. But those bacteria aren’t going to be found in your food, they’re going to be lurking in deep sea hydrothermal vents and hot springs.
So freezing does kill some kinds of bacteria, but it isn’t going to be killing the stuff that makes your food go bad, because those strains of bacteria evolved mechanisms to survive freezing and thawing before multi-cellular life existed on this planet.
And there are also plenty of species of multi-cellular organisms that can survive freezing. Yeah, humans and cats and dogs can’t. But other kinds can freeze solid and thaw out and get on with business. Or they at least have a stage in their life cycle that can survive freezing solid. If they couldn’t half of planet Earth would be a lifeless desert.