What will happen if the egg is overcooked?
When eggs are overcooked, the protein web becomes so tight and retains so little water that the egg white becomes rubbery and the yolk chalky, a textural difference due to fat interspersed with the protein web in the yolk. To better understand how heat affects eggs, think of a fried egg.
Are burnt hard-boiled eggs safe to eat?
Yes, it is safe to eat. This green colour is caused by overcooking the egg and is due to the high amounts of sulphur and iron reacting with the surface of the yolk.