The reason why the yolk has a green layer?

Actually, the green layer on the egg is due to the way it is boiled, not because the egg has any strange substance. When we boil/steam the egg too much, this green color will appear. That is because under the influence of heat for too long, the hydrogen sulfide (H2S) in the egg white will react with the iron in the egg yolk, forming iron sulfide FeS which is blue-black.

That is why the green layer is created on the yolk, where it comes into contact with the egg white, while the yolk inside remains yellow and does not turn green all over the yolk.

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