The 'Century Egg' (or Pidan) is a Chinese delicacy made by preserving duck, chicken, or quail eggs in a mixture of clay, ash, salt, quicklime, and rice hulls for several weeks to months. Contrary to its name, it does not take 100 years to make. The process is a form of alkaline fermentation. The high pH of the surrounding mixture (around 9 to 12) causes the proteins in the egg to denature and the lipids to break down. This turns the egg white into a dark brown, translucent jelly and the yolk into a dark green, creamy substance with a strong smell of sulfur and ammonia. Historically, the eggs were said to have been discovered during the Ming Dynasty when someone found duck eggs in a pool of slaked lime.