In southen China, the "Hundred-Year-Old Egg" is a very popular side dish for breakfast. Called pidan, it is a black-brown colored, hard-boiled egg with a translucent egg while, a grayish blue yolk and a distinct sulfur smell. Most Chinese like to dip the pidan in soy sauce and eat it with breakfast congee.
Most foreingers cringe when they see this Chinese delicacy. Both the sight and the smell are so unusual that many people find it revolting. But it really can be quite delicious when cooked into congee with minced chicken.
Contrary to its looks, pidans are not rotten eggs that have been kept for a hundred years. They are made from fresh duck eggs wrapped in layers of mud and straw, and then placed in lye for at least a month. Apparently, the basic properties in lye ‘cooks’ the egg and hardens it so that the egg appears hard-boiled after the process.