Hundred-Year Eggs are a type of Chinese preserved egg with a greenish and cheese-like yolk 1 and a transparent, gelatinous white with a brownish-yellow to amber color, but which can appear solid black on the outer surface.
The Chinese actually have several ways for preserving eggs, including simple brining, but hundred year eggs are the most interesting and pungent due to the many small flavor compounds created by the process.
They are also called thousand year eggs, millennium eggs, century eggs, ancient eggs, Pidan eggs or Ming Dynasty eggs.
These eggs have a flavor and texture that is surely an acquired taste, but is considered a delicacy by any Chinese, and taste much better than they smell.
The smell of sulfur and ammonia would probably dissuade most Westerners from trying one, but they are said to taste like cheese.
The eggs can be made from chicken, duck, quail, or other bird eggs, but are most commonly made from duck eggs. Although the eggs may appear to have been buried for a hundred or more years, they are actually only preserved for a period of months. Making hundred-year eggs is a long process, and may be quite involved. People usually don’t make these at home, but buy them at market.
There is not only one method for making hundred-year eggs, but the processes involve coating the eggs in a muddy paste made with water, salt, ash, and lime, and covering them with rice husk or some material to keep them from sticking together or to anything else. The eggs are aged for a period of time in an earthenware jar or buried in the ground. Another method, which takes longer, is to first soak the eggs in a water, salt, lime, lye, and tea leave solution for three months. Then the eggs are covered with a paste similar to that already described, and buried for aging. Aging periods may be from 45 days up to even 100 days, depending on the method (and probably the opinion of the maker as to the proper period). One hundred days is the period most often given.
The preservation comes from the raising of the pH of the eggs to 9 or 12, making them quite alkaline. The ingredients primarily responsible for this change are the wood ash and lime.
Before a hundred-year eggs can be eaten, the muddy stuff must be removed and the shell carefully cleaned. The smell of ammonia is the first thing that will hit you, along with the not surprising sulfuric taste. They are usually eaten uncooked in various ways, but are sometimes fried or steamed. They are often eaten for breakfast along with hot rice, or for a late night supper or snack. Soy sauce or a dip made with ginger and vinegar might be used, or the hundred-year eggs might be cooked along with fresh eggs, etc. They are served at Chinese wedding banquets along with a variety of cold foods.
Hundred-year eggs are available at most Chinese grocery stores, and may be served in Chinese restaurants, such as in congee. Recently, there was a controversy involving Chinese factories using toxic chemicals to speed up the process of making hundred-year eggs. Thirty Chinese food plants were shut down for using copper sulphate, which may contain very high levels of dangerous heavy metals. See more on this story at SmithsonianMag.com