A century egg sliced open
|Alternative names||preserved egg, hundred-year egg, thousand-year egg, thousand-year-old egg, millennium egg, black egg, blacking egg, skin egg|
|Place of origin||China|
|Main ingredients||Egg preserved in clay, ash, salt, quicklime, and rice hulls|
|Variations||duck, chicken or quail eggs|
Century eggs (Chinese: 皮蛋; pinyin: pídàn; Jyutping: pei4 daan2), also known as preserved eggs, hundred-year eggs, thousand-year eggs, thousand-year-old eggs, millennium eggs, skin eggs, or black eggs, are a Chinese preserved egg product made by processing duck, chicken or quail eggs in a mixture of clay, ash, salt, quicklime, and rice hulls for several weeks to several months, depending on the method of processing.
Through the process, the yolk becomes a dark green to grey color, with a creamy consistency and strong flavor due to the hydrogen sulfide and ammonia present, while the white becomes a dark brown, translucent jelly with a salty flavor. The transforming agent in the century egg is an alkaline salt, which gradually raises the pH of the egg to around 9–12, during the curing process. This chemical process breaks down some of the complex, flavorless proteins and fats, which produces a variety of smaller flavorful compounds.
Some eggs have patterns near the surface of the egg white which are likened to pine branches. These patterned eggs are regarded as having better quality than the normal century eggs and are called Songhua eggs, also known as pine flower eggs or pine-patterned eggs (Chinese: 松花蛋). In 2014, 3 million tons of Songhua eggs were consumed in China.