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Anne Marie Helmenstine, Ph.D.

Why Egg Yolks Turn Green

By March 28, 2014

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Have you ever wondered how to avoid getting the green ring around the egg yolk of boiled eggs? The green ring forms when you overheat the egg, causing hydrogen and sulfur in the egg white to react and form hydrogen sulfide gas. The hydrogen sulfide reacts with iron in the egg yolk to form a grayish-green compound where the white and yolk meet. While the color isn't particularly appetizing, it's fine to eat. You can keep the yolk from turning green by chilling the eggs as soon as they have finished cooking. One way to do this is by running cold water over the hot eggs as soon as the cooking time has elapsed.


August 11, 2010 at 4:57 pm
(1) Karen says:

I just started researching this green yolk issue. All I seem to be able to find is it’s the process of boiling the eggs that causes the green ring. I’m still confused because I boiled 6 eggs from the same carton. A couple of eggs were the perfect color and the rest had the green ring. They all were boiled in the same pot, same time.

August 7, 2011 at 3:35 pm
(2) GeorgeChao says:

That means the shell of the egg was weak at some point During coception a sliver of air penetrated to the egg yolk. Once the egg yolk comes in contact with the air it turns greens.It will change color from Yellow,Orange,Red yolks to Greeen, drown , black if it sits there for a long time. The eggis still eatable because we have Perservered eggs in our super markets which have black yolks and black jelly like outters. Pretty amazing =)

April 22, 2012 at 3:28 am
(3) Say What George says:

That sounds like a bunch of nonsense there George. The shell of an egg allows air through normally. The reason most eggs crack when you add them to a pot already boiling is that the air trying to escape expands too rapidly and damages the shell. If you put the eggs into water and bring them up to boil, the air escapes more slowly and you can see that evidence as you see them bubble out. It’s just chemistry and technique that cause the green. I haven’t seen the green since I began using the easy hard boil technique. Eggs generously covered with water, bring the pot to a boil, turn OFF heat immediately and let them cook in the water for 15 minutes. They will stop cooking I’ve read when the water drops to 160 degrees anyway. In the meantime I put a bowl of cold water in the freezer to cool it. After the 15 minutes of eggs cooking in the pot (again, the heat should’ve been off long ago) drop the eggs into the cooled water for a few minutes and they’re done. Best hard boiled I’ve ever had.

April 22, 2012 at 3:31 am
(4) George says:

Nevermind, I just misunderstood.

August 1, 2013 at 2:28 pm
(5) Marcus says:

Thank you Anne Marie Helmenstine. Your answer is the correct one and most educated.

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