Hi! While unfreezing my ice box I put various groceries on the porch, as it is around -5°C at the moment. When I checked the packaging, I noticed that the date the food was supposed to be consumed by, varied widely, depending on the temperature. From 3 days (-5°C) to around a year (-15°C). How does it make that big of a difference? Is the water not equally frozen at both temperature points?
In: 4
Part of the answer that’s not yet mentioned is sublimation. Water freezes at zero, but it also **still evaporates** below zero.
Sublimation is why wet laundry hung out to dry on a winter clothesline will still eventually dry even below zero, why older icicles start looking “eroded” after a few days of very-cold breezy weather, and (the most relevant example) why icecubes shrink in your freezer over time. Some of the water molecules in below-zero ice translate directly from solid to vapor.
The more energy in the air, the more sublimation will occur. And in your fridge or freezer, a tiny bit of moisture still evaporates from the surface or near the surface of your food unless it’s vacuum-sealed and all air has been removed.
At -5 it happens a little faster than -15 because it’s still… warmer.
Now, *losing that moisture changes your food.* That leached-away moisture doesn’t go back INTO the food when it condenses back into ice. It’s either removed from the freezer and replaced with drier air, or it resettles as ice crystals on a surface.
If any part of your food is exposed, even IN a sealed package that has some air-space, it can get “freezer-burned” and change appearance or texture or flavour. And this happens faster at -5 than -15.
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