That strange green halo around your yolk isn’t a sign of bad eggs or bad luck. It’s a simple chemical reaction: iron from the yolk meets sulfur from the white when the egg is heated too long, forming harmless but unappetizing iron sulfide. The longer and hotter the cook, the stronger that color and sulfurous smell become, and the more your eggs feel chalky instead of tender.

The fix is all about gentle heat and fast cooling. Start your eggs in cold water with a few centimeters covering them, bring to a clear boil over medium heat, then cut the flame immediately. Let them sit, covered, in the hot water for 9–12 minutes depending on size and desired firmness, then plunge them into ice water to stop cooking and prevent the ring. Peel under cold running water, use slightly older eggs for easier peeling, and you’ll finally get hard‑boiled eggs that look as good as they taste.