We have all experienced this. You open a freshly boiled egg and find a dull green-gray ring circling the yolk. It looks like a cooking mistake, but it is actually a simple and completely avoidable reaction. The good news is that you do not need professional cooking skills to prevent it. A few small adjustments to your method can make all the difference.
What Causes the Green Ring?
The green halo has nothing to do with freshness or spoilage. It occurs because of a reaction between iron in the yolk and sulfur in the egg white. When eggs are cooked for too long or at too high a temperature, these elements combine to form iron sulfide. It is harmless. However, it does affect appearance.
The No-Fail Method for Perfect Boiled Eggs

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Start with Cold Water
Place the eggs in a single layer in a pot and cover them with cold water, with at least one to two inches above the eggs. -
Heat Gently
Set the pot over medium heat, and once the water reaches a rolling boil, turn off the heat immediately. -
Let Them Sit
Cover the pot and leave the eggs in the hot water for 9 to 12 minutes.
. For soft-set yolks, leave them for 9 minutes
. For firm yolks, leave them for 11 to 12 minutes -
Cool Quickly
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