How Everything Works
How Everything Works How Everything Works

Question 315

How does a microwave oven defrost foods? Doesn't it only work with water, not ice?
In any frozen food, there are some water molecules that are relatively free to turn about. These molecules may be at the surfaces of ice crystals or sitting on the surface of food particles. These water molecules can absorb microwaves and heat. However, the heating is very uneven because as soon as any water crystal absorbs enough heat to melt, the resulting liquid water will begin to absorb microwaves much more strongly. That is why defrosting must be done slowly. Then the microwave deposited heat will have time to flow through the food and melt it uniformly. Otherwise, you can end up with boiling hot spots mixed together with frozen icy spots.

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