high-grade eggs with small air cells and
plenty of thick albumen. As eggs age, the
albumen loses water and becomes more dense,
which makes the yolk rise. Industry studies
have found that you can increase the
proportion of centered yolks somewhat by
storing eggs on their sides instead of their
ends. Various cooking strategies have also
been suggested, including rotating the eggs
around their long axis during the first several
minutes in the pot, and standing them on end.
None of these is completely reliable.
Green Yolks The occasional green-gray
discoloration on the surface of hard-cooked
yolks is a harmless compound of iron and
sulfur, ferrous sulfide. It forms at the
interface of white and yolk because that’s
where reactive sulfur from the former comes
into contact with the iron from the latter. The
alkaline conditions in the white favor the
stripping of sulfur atoms from the albumen