Why does the egg's glair turns white when we foam it? What happens to the molecules?

Answer 1

The glair (aka white or albumen) is made up of protein molecules, which are very large. The large size of the protein molecules are what makes the glair thick. When the glair is whipped, as in making meringue, all you are doing is trapping small bubbles of air within. The thickness of the glair holds the foam together. Nothing is really happening to the protein molecules, at least in a chemical sense. The foam looks white only because of light scattering of the bubbles.

When the egg white is cooked, the protein molecules become "denatured"; that is, they are chemically altered in an irreversible way.