Green eggs
Question: I love hard-boiled eggs. My mum makes me them for breakfast at the
weekend. I asked my mum why the yolk goes a funny green colour around the edge,
but she doesn’t know. It doesn’t happen with my sister’s soft-boiled eggs. Can
you tell me why my eggs change colour and why my sister’s don’t?
Answer: The blue-green colour around the yolk of hard-boiled eggs is iron
(ferrous) sulphide. It is produced by a reaction between iron in the yolk and
hydrogen sulphide in the white—which is why you see it around the edge
where the…
