On Food and Cooking

the so-called “thousand-year-old” duck eggs,
which actually have only been made for about
500 years, take between one and six months to
mature, and keep for a year or so. They owe
their popular name — the Chinese term is
pidan, or “coated eggs” — to their startlingly
decrepit appearance: the shell encrusted with
mud, the white a transparent brown jelly, and
the yolk a semisolid, somber jade. The flavor
too is earthy and elemental, eggy in the
extreme, salty, stonily alkaline, with strong
accents of sulfur and ammonia. Pidan are
toned down by rinsing the shelled egg and
allowing it time to “breathe” before serving.
They are a delicacy in China, and are usually
served as an appetizer.
There are only two essential ingredients
for making pidan, in addition to the eggs: salt,
and a strongly alkaline material, which can be
wood ash, lime, sodium carbonate, lye
(sodium hydroxide), or some combination of
these. Tea is often used for flavor, and mud to