Boiled Eggs and Grey Coatings on Yolks

Often when eating a hard boiled egg, you may have noticed a grey or greenish grey coating inside the white and over the yellow portion of the egg. Have you ever wondered what it was? Or how it came to be there? Here we explain what the stuff is and how it shows up in your boiled egg.

The egg white is a mixuture of nearly 148 different types of proteins. It also has 92% water content. The three primary protiens are ovalbumin, ovotransferrin, and ovomucoid. When the egg is boiled the sulphur bonds between the amino acids unravel.

The unraveled bonds then get tangled up with their neighbors and become a solid mass. Hydrogen also reacts with sulphur at a temperature of above 70 degrees Celsius to form hydrogen sulphide. This is the greenish grey color that surrounds the yolk.

In case you don’t want this colour to show up in your boiled egg, you can run the boiled eggs under cool water once they are done. As the temperature is lowered fast the hydrogen sulphide ring does not form. Now you know what science experiment to conduct the next time you get stuck with cooking your own eggs for breakfast.