The most famous of preserved eggs are 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.