That green ring around the yolk of a hard-boiled egg is caused by a chemical reaction between sulfur in the egg white and iron in the yolk. It forms iron sulfide, which has a greenish-gray color.
It usually happens when:
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🥚 The egg is overcooked or heated for too long.
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🌡️ The egg is cooked at a high temperature.
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🧊 The egg isn’t cooled quickly after cooking.
Is it safe? Yes. The green ring is harmless and doesn’t mean the egg has gone bad. It may just have a slightly rubberier texture or stronger sulfur smell.
For a bright yellow yolk, cook the eggs gently and cool them immediately in ice water after cooking.
