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This is an old age trick: if you have some bread that became dried and you put it in the microwave few tens of seconds (10 to 30 for top results) you get a nice soft and warm loaf as if it just came out of the bakery.

I am not sure about the explanation, I cannot decide among two possibilities (and maybe there are other that I did not think of?).

First possible interpretation: the microwaves are absorbed by the covalent bounds in the dried bread molecules and this makes the structure lose its rigidity. The energy absorbed is used to break some of the bounds, making the structure soft.

Second possible interpretation: the microwaves are absorbed by the water molecules in the air, which then are trapped by the much colder dried bread and rapidly diffuse through it, restoring its original softness.

The first interpretation explains better how the inside of the bread is made soft, while the second makes more sense with the usual fact that water absorbs microwaves and gives a reason for the water vapor exaling from the bread when you open the microwave oven. Which is the correct explanation?

Also: the fact that you see vapor means that the water that was originally in the air underwent a sort of (half baked) phase transition?

It is possible that both the effects I thought play a role, even so I would expect one to be dominant. I don't know how realistic is to microwaves to be absorbed and break covalent bounds..

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It is simply because it releases water vapor.

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