Everyday things vaguely to do with physics: 2 — defrosting

Here’s probably quite a well-known trick, but one that has a nice physics-y explanation. Defrosting things to cook can take quite a lot of time depending what they are, requiring forward planning, leaving the thing out overnight, etc. Failing that, there’s the option of defrosting in a microwave, which can have mixed results (e.g. the outside of a thing semi-cooks in a horrible way while the inside stays frozen), and can be dangerous for things like meat because it results in large parts being very slightly, germ-growingly warm for a long time without getting hot enough to kill any germs.

A nice way of getting around this is to put whatever’s being defrosted in a bowl full of cold water. Liquid water is much better than air at conducting heat energy away from (or in this case, towards) something else. So, even though the water is no warmer than the air around it — and in fact can’t get warmer than room temperature, reducing the chances of germs growing — the thing defrosts much more quickly than it would otherwise.

This works especially well for things like vacuum-packed frozen chicken breasts or other meats, where the thing being defrosted can be in more or less direct contact with the water, without any insulating layer of air around it. Happy defrosting and subsequent cooking!

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