That unappetizing green ring is actually a harmless chemical reaction. When eggs are cooked too long or at too high a temperature, the iron in the yolk reacts with sulfur in the white, creating iron sulfide on the surface of the yolk. It looks off-putting, but it’s completely safe to eat and doesn’t mean the egg has gone bad or lost its nutritional value.

To keep your yolks bright and golden, focus on gentle heat and rapid cooling. Bring water to a boil first, then lower in the eggs, reduce to a simmer, and cook for about 9–12 minutes, depending on egg size. As soon as they’re done, plunge them into an ice bath or very cold water to stop the cooking. This not only helps prevent the green ring, it also makes peeling easier—especially if you use slightly older eggs. With just a bit of timing and temperature control, you can finally get clean, yellow yolks every time.