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Is The Grey Lining Around Egg Yolk Harmful To Body?

Do you ever wonder if the grey lining around a hardboiled egg yolk is safe for consumption?  Let us discuss the formation of grey lining and if it is safe for consumption.

Egg white contains proteins that are made up of a complex system of amino acids, held together by sulphur bonds. In total, proteins make up approximately 10% of the chemical composition of egg whites.


When eggs are cooked, sulphur bonds that hold amino acids together in the egg white break and the proteins unravel to bind with each other. This reaction causes the colour and texture of the egg white to change from transparent and viscous to white and solid.


Written by,

Adam John Douch, BSc Nutrition, University of Nottingham



McGee, H., 2004. Eggs. In: On Food and Cooking: The Science and Lore of the Kitchen. New York: Simon & Schuster, pp. 68-89.

Tinkler, C. & Soar, M., 1920. The formation of ferrous sulphide in eggs during cooking. Biochem. J, April, 14(2), pp. 114-9.