Century egg, also known as preserved egg, hundred-year egg,
thousand-year egg, thousand-year-old egg, and millennium egg (or Pidan in
Mandarin), is a Chinese cuisine ingredient made by preserving duck, chicken or
quail eggs in a mixture of clay, ash, salt, lime, and rice hulls for several
weeks to several months, depending on the method of processing. Through the process,
the yolk becomes a dark green, cream-like substance with a strong odor of
sulphur and ammonia, while the white becomes a dark brown, transparent jelly
with little flavor.[citation needed] The transforming agent in the century egg
is its alkaline material, which gradually raises the pH of the egg to around 9,
12, or more.This chemical process breaks down some of the complex,
flavorless proteins and fats, which produces a variety of smaller flavorful
compounds.
Some eggs have patterns near the surface of the egg white
that are likened to pine branches.
The origin of the method for creating century eggs likely
came about through the need to preserve eggs in times of plenty by coating them
in alkaline clay, which is similar to methods of egg preservation in some
Western cultures. The clay hardens around the egg and resulted in the curing
and creation of century eggs instead of spoiled eggs.
Myth
Picking up century egg by Mandru in Incheon.
According to a persistent myth, century eggs are, or were
once, prepared by soaking eggs in horse urine. The myth may arise from the
pungent odor of ammonia given off by century eggs, which is reminiscent of
urine.Horse urine itself, however, is only slightly basic, ranging in pH
from 7.5 to 7.9. Though human urine left standing can reach a maximum pH of
around 9.4—the same as a 1-molar solution of ammonia—it is still less than that
produced by mixing quicklime (calcium oxide) or wood ash in water.