Eggciting question!

[Liquiduk]

So I am at work tucking in to my tuna & egg salad for lunch when I notice my hard boiled eggs have grey rings around the yolk!

A quick google would suggest when boiled and left to cool naturally the grey ring around the yolk tends to happen but when plunged in to cold water to cool quicker the yolk stay yellow.

What do?

 

[Liquiduk]

Its a reaction between the sulfur in the egg white and the iron in the yolk caused by overcooking

Thank you!