Why Hard-Boiled Eggs Sometimes Have a Green Ring—and How to Avoid It

The green or gray ring around hard-boiled egg yolks is caused by a harmless chemical reaction between sulfur in the egg white and iron in the yolk. When eggs are overcooked or boiled at too high a temperature, sulfur compounds release hydrogen sulfide gas, which reacts with iron to form ferrous sulfide—the greenish-gray ring.

While it looks unappetizing, the ring is safe to eat and doesn’t affect flavor or nutrition. To prevent it, avoid overcooking by boiling eggs for 9–12 minutes, use fresh eggs, and lower the heat to a gentle simmer instead of a rolling boil. Cooling eggs quickly in ice water stops the cooking process and limits the reaction. Steaming eggs is another method that reduces discoloration.

Using these tips will help you enjoy perfectly cooked eggs with vibrant yolks and no unwanted green rings.