What causes the green ring between yolk and white when hardboiling an egg?
The yolk of a hardboiled egg often has a green tinge right at the interface to the white. Besides not looking very good, I think it also maybe contributes a sulfurous odor. What causes this green coloration and how can I prevent it?
Best Answer
This is caused by overcooking the egg. The green color is a result of overheating causing the iron and sulfur compounds in the egg to express. You can prevent it by gently boiling the egg, and plunging it into an ice bath when it is done. This stops the carry-over heat from continuing to cook the egg.
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A: The green ring around the yolk of a hard cooked egg happens because hydrogen in the egg white combines with sulfur in the yolk. The cause is most often related to boiling the eggs too hard for too long. The green ring can also be caused by a high amount of iron in the cooking water.What does it mean when you crack an egg and its green?
WHITES THAT AREN'T WHITE yellow means the egg is old; green can mean an excess of riboflavin in the diet, or that a bird has eaten a weed called shepherd's purse; dark green indicates a bird has eaten oak or acorns (especially in ducks);Why is there a black ring between the white and yolk of a boiled egg?
It happens because the iron from the yolk reacts with hydrogen sulfide from the white when it's been overcooked. Totally harmless, but it doesn't have to happen.WHY THERE'S A GROSS GREEN RING AROUND THE YOLK OF YOUR HARD BOILED EGG AND HOW TO AVOID IT!
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Answer 2
I agree over-cooking discolors the yolks. Here's a very detailed analysis of boiling eggs: The Food Lab: Perfect Boiled Eggs. With a recipe for perfect boiled eggs based on this analysis.
Some interesting, relevant excerpts:
The Temperature Timeline of Boiling an Egg
Egg yolks, on the other hand, follow a different set of temperatures:
- At 145 degrees: They begin to thicken and set up.
- At 158 degrees: They become totally firm, but are still bright orange and shiny.
- At 170 degrees: They become pale yellow and start to turn crumbly.
- 170 degrees-plus: They dry out and turn chalky. The sulfur in the whites rapidly reacts with the iron in the yolks, creating ferrous sulfide, and tinging the yolks.
...
So long as your water never come above 180 degrees—at sea level, that's the quivering stage just below a simmer—you have no chance of overcooking
Also the comments are quite interesting. Just search for "green". Not sure if this works, but one commenter suggests a method for avoiding the green coloration:
I watched Chef Pepin's cookshow once he taught the audience an important trick: to poke a tiny hole at the broad end of the egg (using a push pin or similar) before boiling. With this you can effectively eliminate the sulfuric smell and taste of the egg yolk, and simultaneously remove the greyish green "rim" around the yolk (which you can see between the egg white and the egg yolk from the pictures above).
This method has work perfectly for me! And these small details are what make a perfect egg!
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Images: Klaus Nielsen, Dana Tentis, Element5 Digital, Skylar Kang