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, the orange pigment in carrots and other plant foods, but from plant pigments called xanthophylls (p 267), which the hen obtains mainly from alfalfa and corn feeds Producers may supplement the feeds with marigold petals and other additives to deepen the color Duck yolks owe their deeper orange color both to beta-carotene and to the reddish pigment canthaxanthin, which wild ducks obtain from small water insects and crustaceans, egg-laying ducks from feed supplements One minor component of the yolk that can cause a major culinary disaster is the starch-digesting enzyme amylase, which has liquefied many a normal-looking pie filling from within (see p 98) Spheres Within Spheres That’s a yolk by numbers and nutrients But there’s a lot more to this concentrated pool of the sun’s rays Its structure is intricate, much like a Chinese set of nested spheres carved from a single block .. .the orange pigment in carrots and other plant foods, but from plant pigments called xanthophylls (p 267), which the hen obtains mainly from alfalfa and corn feeds Producers may supplement the feeds with marigold... may supplement the feeds with marigold petals and other additives to deepen the color Duck yolks owe their deeper orange color both to beta-carotene and to the reddish pigment canthaxanthin, which wild ducks... obtain from small water insects and crustaceans, egg-laying ducks from feed supplements One minor component of the yolk that can cause a major culinary disaster is the starch-digesting enzyme amylase, which