y does a boiled egg have a darkneess 2 the outsidethe yolk?

Answer 1

Why does the yolk turn green? The green-gray color (and the whiff of sulfur smell that often accompanies it) comes from the reaction of iron in the egg yolk and sulfur in the egg white. When heated, the two can combine to make green-gray ferrous sulfide and hydrogen sulfide gas. To avoid getting a green yolk, cook your eggs just long enough to reach the desired doneness—no more. And quickly plunge the cooked eggs into cold water to stop the cooking process and minimize the iron-sulfur reaction.

Answer 2

The egg has been cooked to long.

The exact time for hard boiled eggs depends on the size of the egg. Cook the egg in a pan of simmering (gently bubbling) water for 10-12 minutes depending on the size. Never cook it for longer than 15 minutes. At the end of cooking immediately remove the egg from the pan, cool quickly under cold running water and then crack the shell. This will allow any remaining heat to escape thus preventing the overcooking of the egg which results in a blue/green rim forming around the yolk. For the best results cook eggs that are at room temperature. Slightly older eggs, around 5 days old, are better for hard boiling as they peel more easily than very fresh eggs.

Answer 3

Is this when you've left it to cool down to use it later, e.g. in a salad? I guess you don't see the darkening when you eat the egg hot and freshly boiled?
As the egg cools slowly, the yolk reacts with the white of the egg, and sulphur (which contributes to the yellow colour of the yolk) -based chemicals form. To prevent it, just tip away the cooking water, and refill the pan with fresh cold water. This chills the eggs fast enough to prevent the darkening from happening !

Answer 4

Usually your yolks will darken or turn almost a greenish color if they are overboiled. How long to boil? I still can never get it right! Good Luck!

Answer 5

Sulfur. Which isn't harmful. And depends on the age of your eggs. As long as they're in date, they're still fine.