Why Your Hard-Boiled Eggs Have Green Yolks

Whether you’re making deviled eggs for a summer picnic or whipping up egg salad for sandwiches, it’s disconcerting when you slice open that first egg and discover the dreaded green hard-boiled egg yolk waiting inside. Are they safe to eat — and if so, will they taste weird? What causes a green hard-boiled egg yolk? It’s all about heat. When an egg is cooked for too long and/or at too high a temperature, the sulfur in the egg white combines with the iron in the yolk to create ferrous sulfide, which has a green tint to it. This chemical reaction — which scientists call denaturation — isn’t limited to hard-boiled eggs. Using too much heat can give scrambled eggs and omelets a greenish cast as well. Is it safe to eat a discolored egg yolk? They may look unappealing, but yes. While they might be visually off-putting and have a bit of a chalky texture, they are safe to eat. The ferrous sulfide that’s formed when the egg is overcooked is the same form of iron you find in iron supplements. It’s actually safer to eat an overcooked egg than an undercooked one. So, how do you hard-boil eggs to avoid the green yolks? The best way is to not boil them at all. Instead, remove the eggs from the carton and place them in a saucepan. Fill the pan with enough water to cover the eggs and place over medium-high heat. As soon as the water boils, turn off the heat and cover the pot. Let the eggs stand in the water for 12 minutes, 18 minutes for extra-large eggs. Remove the eggs and immerse them in a bowl of cold water. Once they have cooled, they’re ready to peel.