If you mean a greenish or gray-green circle around the yolk of a hard-boiled egg, it usually means the egg was overcooked or cooked at too high a temperature.
The ring forms when sulfur from the egg white reacts with iron in the yolk, producing iron sulfide. It can look alarming, but the egg is generally safe to eat if it was properly cooked, refrigerated, and hasn’t spoiled.
To prevent the ring:
- Don’t overcook the eggs.
- After boiling, cool them promptly in cold or ice water.
- Store cooked eggs refrigerated.
If you mean a green circle on the eggshell itself, that’s different—tell me what it looks like (or upload a photo), and I can help identify it.
