The Chinese preserved egg (皮蛋, pídàn) or century egg and even thousand-year-old egg is usually a duck egg that has been preserved in a mixture of clay, salt, ash, lime, and rice hulls for several weeks and even months. The result of this chemical process leaves the egg yolk a dark green color and transforms the whites into a translucent, black jelly. The egg will have a different flavor and has an odor of sulfur and ammonia. Some eggs have patterns on their surface that look like snowflakes or pine branches.

The Chinese preserved egg (皮蛋, pídàn) or century egg and even thousand-year-old egg is usually a duck egg that has been preserved in a mixture of clay, salt, ash, lime, and rice hulls for several weeks and even months. The result of this chemical process leaves the egg yolk a dark green color and transforms the whites into a translucent, black jelly. The egg will have a different flavor and has an odor of sulfur and ammonia.

Some eggs have patterns on their surface that look like snowflakes or pine branches.