Why Is My Hard-Boiled Egg Yolk Green? (And How to Get Perfect Yellow Yolks Every Time!)

You’ve done everything right—boiled your eggs, cooled them down, peeled back the shell… only to find a greenish-gray ring around the yolk. Your heart sinks. “Are they bad? Did I ruin them?”
Good news: your eggs are perfectly safe to eat. That green ring isn’t mold, spoilage, or a sign of old age—it’s just a harmless (but unsightly) chemical reaction. And with one simple tweak to your method, you can avoid it forever.
What Causes the Green Ring?
It’s all about chemistry and timing:
Egg yolks contain iron.
Egg whites contain sulfur.
When eggs are overcooked or boiled too vigorously, the sulfur turns into hydrogen sulfide gas.
This gas reacts with iron in the yolk to form ferrous sulfide—a greenish-gray compound that settles at the yolk’s edge.