The Thousand-year-old Egg (Video) (IMAGE) American Chemical Society Caption Century eggs, or pidan, are a preserved food made by fermenting duck eggs in alkali. The green and black color of these eggs is not very appealing at first blush, and the smell is even worse. However, this Ming dynasty innovation effectively extended the shelf life of eggs and has been adopted as a beloved comfort food in China and throughout the world. Reactions explains the chemistry behind this unusual culinary offering. Credit The American Chemical Society Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.