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KITCHEN TIPS AND TRICKS

Why your hard-boiled egg has a green ring yolk

Find out what causes it and if it is safe to eat.

In Summary

•The reaction is often caused by boiling for too long or a high amount of iron in the cooking water.

•The green ring is harmless and safe to eat.

Hard boiled eggs with green rings around the yolk
Hard boiled eggs with green rings around the yolk
Image: Getty Images

Making perfect eggs is something most of us struggle with in the kitchen.

A perfect hard-boiled egg has a uniform yellow colour. Perhaps you have hard-cooked an egg only to discover a green ring around the yolk when you crack it open.

Here is what happened and what you can do to avoid it:

First and foremost, the unattractive greenish-grey ring may appear around the yolk, after a chemical reaction that involves sulfur (from the egg white) and iron (from the egg yolk), which naturally react to form ferrous sulfide at the surface of the yolk.

The reaction is often caused by boiling for too long or a high amount of iron in the cooking water.

The green ring is harmless and safe to eat.

Tips and tricks:

  • Place eggs in a single layer in a saucepan. Then add cold tap water and cover by at least 1 inch above the eggs.
  • Cover the pan and bring it to boil; once it has boiled, turn off the burner and remove it from heat.
  • Let stand for 15 minutes for large eggs (12 minutes for medium eggs and 18 minutes for extra large eggs).
  • Immediately run cold water over the eggs. This helps the green from forming around the yolks.
  • Store hard-cooked eggs in the refrigerator with the shell and use them within 3 days.
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