A century egg is a Chinese preserved egg that has been cured in a strongly alkaline mixture until the white transforms into a dark, translucent jelly and the yolk becomes a creamy, greenish-black center. Despite the name, the process takes weeks to months, not a hundred years. Duck eggs are the most common base, though chicken and quail eggs are also used. The result is a striking, intensely flavored ingredient that tastes nothing like a regular egg.
How Century Eggs Are Made
The transformation starts with an alkaline bath. Raw eggs are either soaked in a brine of sodium hydroxide and salt or coated in a paste of quicklime, ash, salt, clay, and rice hulls. In both methods, the alkaline solution slowly penetrates the shell and membranes, raising the pH inside the egg high enough to fundamentally change its chemistry. A traditional duck egg recipe calls for a solution of roughly 4% sodium hydroxide and 5% salt, with the eggs left to cure for 20 to 50 days depending on the technique.
As the alkali seeps in, proteins in the egg white denature and re-bond into a firm gel without any heat. The white turns brown or greenish-brown and becomes semi-translucent, almost like dark amber. Meanwhile, the yolk darkens to a deep green or grey-black and develops a soft, creamy consistency. Fats and proteins break down into free amino acids, peptides, and fatty acids, which together create the egg’s distinctive savory, sulfurous flavor.
The traditional coating method is the slowest: eggs are individually wrapped in the alkaline paste, which dries and hardens into a crust over several months. A faster modern approach soaks raw eggs in a salt, calcium hydroxide, and sodium carbonate solution for about 10 days, then ages them in a sealed container for several more weeks. Black tea is sometimes added to the curing mixture, contributing to the color and subtle flavor complexity.
Flavor and Texture
Century eggs have a rich, complex taste that’s often described as deeply savory with notes of sulfur and ammonia. The intensity varies. A well-made century egg has a clean, concentrated umami flavor, while a poorly cured one can smell overwhelmingly of ammonia. The white is firm and bouncy, similar in texture to a stiff gelatin. The yolk ranges from custard-soft to almost paste-like at the center, sometimes with a slightly gritty quality. Some eggs feature delicate, snowflake-like crystal patterns on the surface of the white, which are considered a sign of quality.
Nutrition Compared to Fresh Eggs
The curing process concentrates protein while reducing fat. A whole century egg contains about 13.1% protein compared to 9.3 to 11.8% in a fresh duck egg. Fat drops slightly to around 10.7%, down from the 11.4 to 13.5% range in fresh eggs. The yolk’s cholesterol content also decreases during preservation: cholesterol in the yolk oil falls from about 38% in fresh eggs to roughly 29% in century eggs.
Mineral content increases because the egg absorbs sodium and other elements from the curing solution. Century eggs are noticeably saltier than fresh eggs, which is one reason they’re typically served in small portions alongside other ingredients rather than eaten alone.
Safety and the Lead Question
Traditional century egg recipes sometimes included lead oxide or zinc oxide to speed up the curing process. These heavy metals helped the alkaline reaction work faster, but they also left residues in the finished egg. This is the source of the long-standing safety concern around century eggs.
Modern production in most countries has moved away from heavy metals entirely. Health Canada prohibits the addition of lead to any food product, and food safety authorities like the BC Centre for Disease Control explicitly recommend against using lead oxide, zinc oxide, or copper sulfate in century egg production. When shopping for century eggs, look for packages labeled “lead-free” (无铅 in Chinese). Most commercially produced century eggs sold in North America, Europe, and East Asia now use lead-free formulas, relying only on sodium hydroxide, calcium oxide, and salt.
The high alkaline environment inside a century egg does serve as a natural barrier against common foodborne pathogens. Bacteria like Salmonella struggle to survive at such elevated pH levels, which is part of what makes alkaline preservation effective in the first place.
How Century Eggs Are Served
The most iconic use is in congee, the slow-cooked rice porridge eaten across China and Southeast Asia. Century egg and pork congee pairs diced century egg pieces stirred into the porridge with strips of lean pork, then tops the bowl with century egg wedges, chopped cilantro, and green onions. The mild, starchy congee balances the egg’s strong flavor, and the pork adds a contrasting clean meatiness.
Century eggs are also commonly served cold as an appetizer. A popular preparation involves quartering the eggs and drizzling them with a sauce of soy, black vinegar, sesame oil, chili, and minced garlic. The vinegar is key: its acidity cuts through the egg’s alkaline richness. Silken tofu topped with chopped century egg and a similar dressing is another staple, especially in summer. In some dim sum restaurants, century egg appears in steamed buns or alongside pickled ginger as a palate cleanser.
If you’re trying century egg for the first time, congee or the cold tofu dish are the gentlest introductions. Eating a whole century egg on its own can be overwhelming, but when it’s balanced with rice, vinegar, or fresh herbs, the flavor becomes much more approachable.