Shocking them in ice-cold water stops the cooking process. This not only yields more tender whites and a perfectly cooked yolk (no weird dark lines here), it immediately cools the eggs which makes them easier to peel.
Shocking hard-boiled eggs — that is plummeting them into a bowl of ice water — right after boiling also makes an easier-to-peel egg. The rapid cooling of the eggs contracts the egg whites, releasing them from the egg's membrane. It also firms the egg white proteins, making them easier to peel.
Ideally, peel the eggs as soon as they're cool. Start at the broad end, and hold the egg under running water to loosen any bits of stubborn shell clinging to the sides.
Leave eggs in the ice bath for 10+ minutes to allow for thorough cooling/easy peeling (you can place them under running cold water instead, but without the cold shock from the ice bath, you may have a harder time peeling, especially if your eggs are farm fresh like ours).
This is because the egg white or “albumen” in a fresh egg has a relatively low pH level, making it acidic. When cooked, these fresh egg whites bond strongly to the inner shell's membrane. As an egg ages, the pH level rises and the inner membrane is less likely to bond to the albumen, so the shell peels off much easier.
Apparently super fresh eggs are difficult to peel because the pH of the white is more acidic which causes it to adhere to the shell membrane more tightly. Two solutions here – use older eggs or add a little bicarb soda to the cooking water to increase the pH.
Transfer the eggs to a bowl of ice water and chill for 14 minutes. This makes the eggs easier to peel.
The soonest time to peel hard boiled eggs is after they have sat in cold or ice water for ten minutes. Give them at least this long, to prevent overcooking and make the peeling process easier.
Once the eggs have cooked to your preferred time, use the skimmer to remove the eggs and immediately submerge them in the ice water bath to stop them from cooking. You'll let the eggs sit here for about 5 to 10 minutes before peeling.
As with all cooked foods left out at room temperature (aka the Danger Zone), hard-boiled eggs are no longer deemed safe after two hours.
Starting with cold water lets you heat the egg more slowly, which keeps the whites from getting rubbery. But this method takes longer and gives you less control over the cooking time.
When you plunge the eggs into a bowl of ice and water, the shock of the cold water stops the cooking process, preventing them from overcooking, explains The Spruce Eats. Otherwise, the residual heat in the eggs will continue to cook them, even after they have been removed from the source of heat.
As a rule, the fresher the egg, the more difficult it is to peel cleanly. The albumen (white) of a just-laid egg contains a store of dissolved carbon dioxide, a weak acid. (CO2 is what makes very fresh raw egg whites appear cloudy.) Over time, the gas exits the egg through thousands of tiny pores in the shell.
The ice water will also cause the egg to contract and pull away from the shell, which will make it easier to peel. Let the eggs sit in the ice bath for at least 5 minutes. If you live in a climate where tap water runs very cold, you can run cold water over the eggs for 5 minutes rather than preparing an ice bath.
“What would happen if you let a hard-boiled egg just keep boiling?” — Drew H., Oakland, Calif. If you boil an egg for five or 10 minutes, it becomes firm and cooked. If you boil it for hours, it becomes rubbery and overcooked.
Hard-cooked eggs, which have been quickly cooled and placed in the refrigerator in their shells should be consumed within seven days. Peeled hard-cooked eggs stored in the refrigerator should be consumed within 48 hours due to the moist egg white surface being exposed and the potential of microorganism growth.
Keeping Hard-Boiled Eggs Fresh
For maximum freshness, leave them in their shells until you are ready to eat or prepare. The shell will help to protect the egg from bacteria, and can help prevent them from absorbing odors from other foods in your refrigerator.