I wonder if anyone knows why the egg yolk in my sausage and egg McMuffin was grey around the edge? I've contacted McDonalds head office who were unable to help - many thanks
"A greenish-gray ring may appear around a hard-cooked egg yolk. It's unsightly, but harmless. The ring is caused by a chemical reaction involving sulfur (from the egg white) and iron (from the egg yolk), which naturally react to form ferrous sulfide at the surface of the yolk. The reaction is usually caused by overcooking, but can also be caused by a high amount of iron in the cooking water."
http://food.unl.edu/how-avoid-green-ring-around-hard-boiled-egg-yolks
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