On Food and Cooking

Three different grades of eggs. The AA egg
has a high proportion of thick white and a
firm, rounded yolk. The A egg has a less thick
albumen and a weaker yolk membrane, so it
spreads more when cracked into a pan. The B
egg spreads even further, and its yolk
membrane is easily broken.
All of these trends are probably part of the
normal development of the egg. The increase
in alkalinity makes the albumen even less
hospitable to invading bacteria and molds.
The thinning of the albumen allows the yolk
to rise and the embryo to approach the shell,
its early source of oxygen, and may make it
easier for the embryo to tap the shell’s
calcium stores. A weaker yolk membrane
could mean an easier attachment to the shell
membranes. And the larger air cell gives the
chick more oxygen for its first few breaths.
These changes may be good for the chick,
but they’re mostly bad for the cook. A thinner