Century egg

Century eggs, (also called preserved egg or 100-year egg) also known as alkalized or preserved eggs, is a Chinese dish made by preserving 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 processing method. Through the process, the yolk becomes dark greenish-grey in color, with a smooth consistency and strong flavor due to the hydrogen sulfide and ammonia present, while the white becomes dark brown in color, with a translucent jelly-like appearance, a gelatinous texture, and a salty and umami 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.

Description: Wikipedia — Century egg, CC BY-SA 4.0