Why does a green ring appear around hard-boiled eggs?

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# Why Does a Green Ring Appear Around Hard-Boiled Eggs?

You slice open a hard-boiled egg, expecting a smooth yellow yolk—and there it is.

A faint greenish-gray ring hugging the outside of the yolk.

It doesn’t look appetizing. It raises questions. And for many people, it sparks immediate concern:

*Is the egg spoiled?*
*Did I cook it wrong?*
*Is it safe to eat?*

The short answer: **yes, it’s safe**—and no, it’s not spoiled.

The longer answer is far more interesting. That green ring is the result of a simple chemical reaction, one that reveals a lot about heat, timing, and the delicate science of cooking eggs.

Let’s break it down.

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## The Green Ring Mystery: What Are You Actually Seeing?

The green or gray ring that appears around hard-boiled egg yolks is caused by a compound called **iron sulfide**.

It forms when two naturally occurring substances in eggs meet under high heat:

* **Sulfur** from the egg white
* **Iron** from the egg yolk

When eggs are cooked too long or at too high a temperature, sulfur from the whites is released as hydrogen sulfide gas. That gas migrates inward toward the yolk, where it reacts with iron to form iron sulfide—creating the greenish-gray ring.

In other words, the ring isn’t decay.

It’s chemistry.

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## Why Overcooking Is the Real Culprit
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