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 create a paste that dries to a protective crust, though the eggs can also be immersed in a water solution of the curing ingredients (this gives a faster cure but also a coarser alkaline flavor) A mild, soft-yolked version of pidan is sometimes made by adding some lead oxide to the cure The lead reacts with sulfur from the egg white to form a fine black powder of lead sulfide, which blocks the shell pores and slows the further movement of salt and alkaline ingredients into the egg (Lead is a potent nerve toxin, so such eggs should be avoided; look for packages clearly labeled “no lead oxide.” A similar effect can be obtained by replacing lead with zinc.) Creating Clarity, Color, and Flavor The real transforming agent in pidan is the alkaline material, which gradually raises the already alkaline egg from a pH of around to 12 or more This chemical stress causes what might be thought of as an inorganic version of ... is sometimes made by adding some lead oxide to the cure The lead reacts with sulfur from the egg white to form a fine black powder of lead sulfide, which blocks the shell pores and slows the further movement of salt and alkaline ingredients into the egg...create a paste that dries to a protective crust, though the eggs can also be immersed in a water solution of the curing ingredients (this gives a faster cure but also a coarser alkaline flavor) A mild, soft-yolked version of pidan is sometimes made by adding some lead oxide... by replacing lead with zinc.) Creating Clarity, Color, and Flavor The real transforming agent in pidan is the alkaline material, which gradually raises the already alkaline egg from a pH of around to 12 or more This chemical stress causes what might