A fermented egg is a preserved duck egg, also known as a "thousand year egg," that is a traditional Chinese delicacy. The egg is prepared by caking it in a mixture of quicklime, salt, and ash, with tea leaves or rice husks sometimes added to the mix. The curing process takes several weeks to months and results in a chemical reaction that increases the sodium content and pH of the egg. During the fermentation, the egg white becomes gelatinous and turns dark brown or black, while the yolk becomes dark green and has a creamy consistency with a strong flavor due to the hydrogen sulfide and ammonia. Fermented eggs are considered an acquired taste and are often used in Chinese cuisine as a snack, appetizer, or incorporated into main courses. They are also known for their health benefits, such as maintaining a healthy balance of beneficial and harmful bacteria in the intestine and regulating stomach acid production.