On Food and Cooking

the egg leaves the hen, it begins to deteriorate
in important ways. There is a fundamental
chemical change: both the yolk and the white
get more alkaline (less acidic) with time. This
is because the egg contains carbon dioxide,
which takes the form of carbonic acid when
it’s dissolved in the white and yolk, but is
slowly lost in its gaseous form through the
pores in the shell. The pH scale provides a
measure of acidity and alkalinity (p. 795). On
the pH scale, the yolk rises from a slightly
acidic pH of 6.0 to a nearly neutral 6.6, while
the albumen goes from a somewhat alkaline
7.7 to a very alkaline 9.2 and sometimes
higher.
This alkalinization of the white has highly
visible consequences. Because albumen
proteins at the pH of a fresh egg tend to
cluster in masses large enough to deflect light
rays, the white of a fresh egg is indeed
cloudily white. In more alkaline conditions
these proteins repel each other rather than