Sometimes a boiled egg sticks to the shell and makes it hard to peel. The culprits are two thin membranes that lie between the white and the shell. The fresher the egg, the stickier the membrane, and the harder the egg-peeling job. There are a few tips and tricks to help make the task easier, however.

Egg Anatomy

Between the shell of the egg and the white lie two thin membranes, simply known as the inner and outer membrane. These membranes are made of a whitish protein called albumen. The outer membrane's job is to cling tightly to the shell; the inner membrane's job is to cling tightly to the yolk. The two membranes also stick securely to each other.

Old Eggs vs. New Eggs

The shells of fresh eggs are more likely to stick than the shells of older eggs. As the egg ages, the inner and outer membrane release carbon dioxide and become less elastic--less sticky. You can easily tell the age of an egg just by observing it in the pot of water prior to cooking. If it lies on its side, it's very fresh. If it stands on its end, it's a bit older, and the air pocket has grown large enough to cause one end to float more easily than the other. If the entire egg floats, it's probably past its prime.

Solutions

One nearly foolproof method to easy-to-peel eggs is to plunge your hard-cooked eggs into a bowl of ice water immediately after removing them from the pot. Wait to peel the egg until it has completely cooled. Supposedly, this helps a thin layer of steam to form between the shell and the membranes. Peeling the egg under cold running water can also help.

Salt And Baking Soda

Some people believe adding a teaspoon or so of salt will help make hard-cooked eggs easier to peel. Others recommend a similar amount of baking soda in the cooking water. No one is quite sure why these methods work, but they seem to help.

Fun Egg Facts

Don't try to cook an egg in the microwave--it will explode! To determine whether an egg is raw or hard-cooked, place it on its side on a countertop or table and spin it. If it spins easily, it's hard-cooked; if it wobbles, it's raw. Chefs prefer the term 'hard-cooked' because it is less misleading. Eggs are cooked at a gentle simmer, not a hard boil; boiling an egg will cause it to be overcooked, and may crack the shell during cooking.

Source:

FIne Cooking: Cracking the Boiled Egg Mystery

What's Cooking America: Boiled Eggs

IncredibleEgg.org: Peeling