You put a pot of water on to boil. When once it does, you add some ordinary chicken eggs to make deviled eggs, chicken salad, or just separate pieces of the “hen fruit” to munch on with a free sprinkling of sea salt.
You experience a problem, however, when you go to peel them. Why don’t your boiled eggs peel right? In fact, sometimes they do, and sometimes they don’t. Why not every time?
Within the eggshell lies more than just a white and a yolk. Between the white and the shell is a thin membrane, rich in keratin—the protein of fingernails, hair, and horns.
This keratinous membrane forms a strong bond to the egg white in a boiled egg, if it is fresh. A fresh egg white possesses a lower pH (higher acidity) than does the egg white of an egg that is not quite so fresh. As the egg ages, the pH rises and the bond between membrane and white lessens.
This means the shell and membrane are more easily removed from the egg—it is easier to peel. A greatly increased number of eggs that are just a bit older, but within the realm of healthy and moderately fresh, will peel just as you want them. So the solution to the peeling problem is allowing just the right amount of aging.
For a more detailed explanation, see the reference, listed below.