Century eggs, also known as pidan, preserved eggs, hundred-year eggs, thousand-year eggs, thousand-year-old eggs, century-old eggs, millennium eggs, skin eggs, black eggs or old eggs are a traditional Asian dish featuring eggs that have been preserved in a curing mixture for several weeks to several months.
The outer egg white turns into a dark brown, translucent jelly, while the inner egg yolk becomes dark green and squishy.