Green eggs

[modge]

Why do the yolks of hard-boiled eggs go green around the edges and not the yolks of soft boiled eggs?

[incitatus]

The yellow comes from iron111 compounds. When eggs are boiled some of the proteins decompose to give hydrogen sulphide, which will reduce the iron 111 to iron11 which is green. This decomposition takes a long time to happen, and needs heat, so a hard boiled egg will do it but a soft one wont. Incidentally to stop it happening boil the eggs for no more than 8 minutes then plunge into ice water. The rapid cooling will prevent the greening.

[SMILL48]

There is an article about green eggs on Answerbank - just click article 3041