A century egg is a duck egg that has been preserved in a mixture of ash, lime, salt, clay and rice for weeks or even months. Also called a thousand-year egg or millennium egg, it is considered a delicacy in China, where the recipe originated thousands of years ago. They are known for an exceptionally strong taste and odor, which is reminiscent of sulfur or ammonia.
After the preservation process is complete, the shell of the egg is speckled, giving it an aged appearance that may have given it is name. When the egg is cracked open more drastic change are become apparent. The white has changed from clear to a dark brown color and is gelatinous in texture. The most notable change though is the in egg yolk. Instead of a bright yellow, it is dark-green/black and has the texture of thick cream or yogurt. Most of the strong smell and taste of the century egg comes from the yolk, which absorbs more of the special fermenting solution during the preservation process.
Some compare the hundred-year eggs to smelly cheeses in both taste and selective appeal. Others describe the taste as resembling a traditional duck egg, just much stronger with an aftertaste that resembles vinegar or ammonia. In America, the egg's off-putting appearance and strong taste made them a popular food of choice for shock game shows that forced contestants to eat gross foods. In China, however they are considered a fine delicacy and are often served as appetizers at weddings and other parties. These eggs may be mixed together with traditional eggs, ground up and used as a topping, or on slices like an orange. They are also found in soups, porridge, omelets and just about any other dish where you might find typical eggs.
The century egg is just one example of specially prepared eggs in Chinese cuisine. The Chinese make many other dishes that involve soaking eggs in special mixtures, including the soy egg and tea egg. The century egg though is the only one that is considered a delicacy, the others are commonly sold as snacks by street vendors. This may have to do with the complex preparation that goes in the creation of the hundred-year egg, or just because its incredibly pungent taste and smell is off-putting for some.
Century eggs remain popular in China and other Asian countries, although the preparation process has changed with new technology. While some still prepare the eggs in the traditional method, many companies who sell the eggs pre-packaged soak them in salt brine, sodium carbonate and calcium hydroxide. Using this method, a century egg can be prepared in less than two weeks, as opposed to a month or more. Some egg makers have resorted to using lead oxide to speed up this process, leading to concerns of lead poisoning and other health problems.