Araucanas and brown-egg breeds make both
blue and brown pigments and thus green
shells.
The completed egg is expelled blunt end
first about 25 hours after leaving the ovary.
As the egg cools down from the hen’s high
body temperature (106ºF/41ºC), its contents
shrink slightly. This contraction pulls the
inner shell membrane away from its outer
partner at the blunt end and thereby forms the
air space, whose size is an indicator of egg
freshness (p. 81).
The Yolk
The yolk accounts for just over a third of a
shelled egg’s weight, and its biological
purpose is almost exclusively nutritive. It
carries three-quarters of the calories and most
of the iron, thiamin, and vitamin A of the egg
as a whole. The yolk’s yellow color comes not
from the vitamin-A precursor beta-carotene,