Why do some hard-boiled eggs have a greenish ring around the yolk?
The harmless greenish ring is due to an iron and sulphur compound that forms when eggs are overcooked or not cooled quickly. This ring can be prevented if the exact boiling time compared to the egg size is applied. The best way to check this is by boiling an egg that weighs approx. 55-62 grams. If the ring is formed it will disappear after a couple of days in brine. The brine consists of water, 1.5-2% salt and 1.5-2% citric acid.
