Why is my boiled egg yolk green?
A grey-green ring around a hard boiled yolk means the egg cooked too long or cooled too slowly. According to USDA it's safe to eat. It just looks tired and can taste a little of sulfur.
What causes the green ring
USDA explains that sulfur and iron compounds in the egg react on the surface of the yolk when it's overcooked. A lot of iron in your cooking water can also cause it. The longer the egg cooks, the more of it you get.
How to stop it happening
- Don't overcook. 10 to 12 minutes is plenty for large eggs, and 13 minutes is about as far as you need to go. The egg timer takes the guessing out.
- Keep the water at a gentle boil, not a hard rolling one.
- Get the eggs into ice water as soon as they come out, and leave them 10 to 15 minutes. A hot egg left to cool on the counter keeps cooking.
The sulfur smell
That eggy smell comes from the same sulfur. Overcooked eggs give off more of it. Eggs cooked to time and chilled quickly smell much milder.
Is a green yolk safe?
Yes. USDA says the green colour is safe to eat. It's a sign of overcooking, not of a bad egg.
A bad smell when you open the egg is a different story, and so is a pink or pearly look to the white, which USDA says points to spoilage. Throw those out. More on how long boiled eggs last.
Questions people ask
Is it safe to eat a boiled egg with a green yolk?
Yes. USDA says the green ring is safe to eat. It comes from overcooking.
Why do my boiled eggs smell like sulfur?
Eggs contain sulfur, and overcooking releases more of it. Cook to time and chill the eggs quickly.
Why is my yolk grey instead of yellow?
Same cause as the green ring: overcooking or slow cooling. Cut the time back toward 11 minutes and use an ice bath.
Does a green yolk mean the egg was old?
No. It's about how the egg was cooked and cooled.