The Science Behind It
When eggs are overcooked or cooked at too high a temperature, the iron in the yolk reacts with sulfur in the egg white to form ferrous sulfide, which has that green or gray color.
Iron (from yolk) + Sulfur (from white) → Ferrous sulfide (FeS)
This compound forms where the yolk and white meet — that’s why you see a ring.
🔥 Common Causes
- Overcooking — boiling eggs for too long.
- High heat — cooking in rapidly boiling water instead of gentle simmering.
- Slow cooling — leaving eggs in hot water after cooking instead of cooling them quickly.
✅ How to Prevent It
Cook gently: Boil water first, then reduce to a simmer before adding eggs.
Timing: Cook 9–12 minutes (depending on egg size).
Cool quickly: Transfer immediately to an ice water bath or cold running water for a few minutes after cooking.
Use fresh eggs: Older eggs are more likely to develop rings due to pH changes.
🥚 Is It Safe to Eat?
Yes — the eggs are completely safe to eat. The ring only affects appearance, not taste or nutrition.