What Are Century Eggs And Are They Really 100 Years Old?

Pidan go by many names, but all of them suggest that these eggs are really old. Century eggs, 100-year eggs, 1000-year eggs, and millennium eggs are all names for the boldly odored, colored, and flavored preserved eggs that originated in China.

Typically they are made using duck eggs, but they can also be made with chicken or quail eggs. The process starts by making a mud-like alkaline mixture of wood ash, salt, clay, and calcium oxide (also known as quicklime) or calcium hydroxide (also called slaked lime). The traditional mix also often includes brewed tea. The eggs are wrapped in this black mud, coated in rice husk, packed into a vessel where contact with the outside air is minimal, and left to cure for anywhere from a few weeks to several months. Commercially produced century eggs can be made in as little as two weeks. So no, these preserved eggs are not really 100 years old, but the dramatic change they go through definitely makes them look like they are.

The chemical reaction between sodium carbonate, water, and calcium hydroxide yields sodium hydroxide, which causes the sodium levels of the egg to increase and the protein in the egg to gelate. The egg white darkens in hue and "ranges from golden amber to an unusual translucent black; its yolk contains merging rings of soft green, yellow, and gray," and texturally, the white becomes gelatinous, but "the center is soft, dark, and oozing," according to Britannica.

What is the history of the century egg?

More than likely, pidan — or century eggs — were first made around 600 years ago during the Ming Dynasty in China, but there are several possible origin stories. One story says that a man in Hunan, China found eggs that had been laid in the construction waste of his house, and of course, he did what anyone would do and ate them. Another story includes a failed attempt at wooing a lady when a man left eggs outside for her, but they weren't found for several months.

Perhaps the century egg was created accidentally by a restaurant owner in Wujiang County in the Jiangsu province. He poured his spent tea leaves into the ashes of a stove where his ducks would sometimes lay eggs — only to discover the preserved eggs later on. Yet another story says that a farmer just happened upon eggs that had been preserved after sitting in a puddle of muddy water and slaked lime.

Are they safe to eat?

The short answer is yes. Century eggs, like many preserved foods, are safe to eat, but it is important to check them for signs of spoilage before eating. While the smell of ammonia will always be present in century eggs, an overwhelmingly bad ammonia odor or moldy stench are signs that things have gone wrong. The shell should be visibly intact with no cracks, holes, or dents. When shaken or tapped, there should be no rattling sound.

It is also important to get century eggs from a reliable source. It used to be common to use lead oxide during the curing process, which does create a century egg that is considered more desirable but also has the unfortunate effect of being toxic to humans. While there are food safety standards in China that restrict toxic levels of lead in food, some century egg producers ignore these metrics for the sake of a "better" final product. The good news is that the majority of century eggs available now are free of lead.

What do century eggs taste like and how are they eaten?

The aroma of these preserved eggs is no doubt pungent, smelling intensely eggy and faintly of ammonia. The taste is salty and complex, with a gelatinous white and creamy yolk. While the smell and certainly the sight can be shocking, Carrel Kam, director of the popular Yung Kee Restaurant in Hong Kong, tells BBC, "It's psychological — just like the idea of blue cheese. The smell is terrible but the taste is good." At Yung Kee Restaurant, century eggs are typically served as an appetizer with pickled ginger. The spicy and sweet ginger acts as a balancing palate cleanser alongside the rich and velvety egg. Century eggs are often served with congee — a simple rice porridge — and century egg congee with lean pork and scallions is a comfort food for many. The eggs can also be served as a simple snack with soy sauce, vinegar, and chilies and pair especially well with an ice-cold beer. They are also popularly served alongside silken tofu with a similar sauce.

At dim sum restaurants, you can find glistening puff pastry pockets filled with century egg. A Hunan preparation mashes the century egg with sauteed chilies, garlic, vinegar, soy sauce, and sesame oil and is served with rice. Century egg is even sometimes mixed with ground pork and steamed to make sausages.

While pidan are certainly something different for the Western palate, these preserved eggs have been enjoyed for centuries and are definitely worth a try.