cluster, so the white of an older egg tends to
be clear, not cloudy. And the white gets
progressively more runny with time: the
proportion of thick albumen to thin, initially
about 60% to 40%, falls below 50–50.
The relatively minor change in yolk acidity
is less important than a simple physical
change. The yolk starts out with more
dissolved molecules than the white, and this
osmotic imbalance creates a natural pressure
for water in the white to migrate across the
yolk membrane. At refrigerator temperatures,
about 5 milligrams of water cross into the
yolk each day. This influx causes the yolk to
swell, which stretches and weakens the yolk
membrane. And the added water thins the yolk
dramatically.
A Home Test Finally, the egg as a whole also
loses moisture through its porous shell, so the
contents of the egg shrink, and the air cell at
the wide end expands. Even an oil-coated egg