[Sca-cooks] **OOP** Hard Cooking Eggs

[Laura L]

Oooooh! very cool! Thanks Avraham! Chemistry rocks!
--Laura L
>
> According to Shirley Corriher, in _CookWise_, "It is accepted
> that the ugly
> green layer on the yolk is the result of iron in the yolk combining with
> sulfur (hydrogen sulfide) in the white to form green iron sulfide. Author
> Harold McGee recently did some experiments in which he got the yolks green
> all the way through, indicating that the yolk alone contains
> enough iron and
> sulfur to produce the green iron sulfide. While the egg is cooking, heat
> speeds up this chemical reaction. The longer the egg cooks, the
> greater the
> chance for discoloration, so watch the time carefully. Quick cooling also
> helps prevent the layer from forming."
>
> McGee himself says in _On Food and Cooking_, "The other oddity about
> hard-boiled eggs is the occasional appearance of a greenish-gray
> discoloration on the surface of the yolk. The color is caused by
> a harmless
> compound of iron and sulfur called ferrous sulfide, which is formed only
> when the egg is heated, especially in the case of an extra-alkaline
> less-than-fresh egg. The yolk contains a good deal of iron, and
> the albumen
> a good deal of sulfur, primarily on side chains in the protein ovalbumin.
> When that protein is heated, some of its sulfur atoms are liberated and
> react with hydrogen ions in the albumen to form hydrogen sulfide (H2S). In
> minute quantities this gas lends a characteristic and pleasant odor to
> cooked eggs and meat, but in larger quantities is the odor we
> associate with
> rotten eggs. As the gas forms, it diffuses in all directions, and some
> reaches the surface of the yolk, where it encounters iron and
> reacts to form
> the dark particles of ferrous sulfide (FeS). The way to minimize the
> discoloration is to minimize the amount of hydrogen sulfide that
> reaches the
> yolk. First, cook the eggs only as long as is necessary to set the yolk.
> Then plunge the cooked eggs immediately into cold water. This lowers the
> pressure of the gas in the outer regions of the white, since cool gases
> exert less pressure than hot, and cool protein loses less sulfur than hot.
> Consequently the hydrogen sulfide diffuses away from the yolk, toward the
> region of lower pressure at the surface. Finally, peel the eggs promptly:
> this also helps pull the gas away from the yolk."
>
> Avraham
>
> ****************************************
> Avraham haRofeh of Northpass
>      (mka Randy Goldberg MD)
> RandomTag: They also serve who only stand and wait.
>
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