On food and cooking the science and lore of the kitchen ( PDFDrive ) 231

the so-called “thousand-year-old” duck eggs,
whichactuallyhaveonlybeenmadeforabout
500years,takebetweenoneandsixmonthsto
mature, and keep for a year or so. They owe
their popular name — the Chinese term is
pidan,or“coatedeggs”—totheirstartlingly
decrepit appearance: the shell encrusted with
mud,thewhiteatransparentbrownjelly,and
theyolkasemisolid,somberjade.Theflavor
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.
TheyareadelicacyinChina,andareusually
servedasanappetizer.
Thereareonlytwoessentialingredients
formakingpidan,inadditiontotheeggs:salt,
andastronglyalkalinematerial,whichcanbe
woodash,lime,sodiumcarbonate,lye
(sodiumhydroxide),orsomecombinationof
these.Teaisoftenusedforflavor,andmudto


createapastethatdriestoaprotectivecrust,
thoughtheeggscanalsobeimmersedina
watersolutionofthecuringingredients(this
givesafastercurebutalsoacoarseralkaline
flavor).Amild,soft-yolkedversionofpidan
issometimesmadebyaddingsomeleadoxide
tothecure.Theleadreactswithsulfurfrom

theeggwhitetoformafineblackpowderof
leadsulfide,whichblockstheshellporesand
slowsthefurthermovementofsaltand
alkalineingredientsintotheegg.(Leadisa
potentnervetoxin,sosucheggsshouldbe
avoided;lookforpackagesclearlylabeled“no
leadoxide.”Asimilareffectcanbeobtained
byreplacingleadwithzinc.)
Creating Clarity, Color, and Flavor The real
transforming agent inpidan is the alkaline
material, which gradually raises the already
alkaline egg from a pH of around 9 to 12 or
more.Thischemicalstresscauseswhatmight
be thought of as an inorganic version of