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I know freezing is supposed to make foods expand but it seems that two pre-packaged sealed food items that I have in my freezer seem a bit puffy (chicken curry and chicken dumplings with cabbage) after taking them out of the freezer.

I don't think they were that way when I bought them but not sure. My freezer seems to working well (although my fridge is a bit variable) and foods always seem well-frozen. And I only left them out less than half an hour.

Can sealed food packages expand when they defrost rather than the other way around? Thanks!

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    Generally, cold makes things contract... heat makes things expand... I think you're just thinking about it backwards. – Catija Jun 25 '15 at 4:55
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    @Catija: but water, which most foods contain a lot of, starts to expand as it cools from around 4 degrees C. – Max Jun 25 '15 at 7:25
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    The food isn't expanding when it warms up, the air in the packaging is. – ElendilTheTall Jun 25 '15 at 9:04
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    @ElendilTheTall Absolutely correct. Many, but not all, manufacturers put a small hole (think pinhole) in the packaging so that frozen products store and defrost without excess air in the package. – Cindy Jun 25 '15 at 13:32
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    @Cindy If you know the answer, post an answer! I'm getting the rep now! – Cascabel Jul 7 '15 at 6:22
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That's just the air in the package expanding, as it goes from freezer temperature to room temperature.

It sounds like you're thinking of the fact that water expands when it freezes (and shrinks when it melts) but that's not what's happening here. The air warms up long before the ice starts melting.

Some freezer packaging has small holes in it (or not so small holes, if you're unlucky), which prevents this from happening.

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