A century egg is a Chinese preserved egg that has been cured in an alkaline mixture until the white turns into a dark, translucent jelly and the yolk becomes a creamy, greenish-gray paste. Despite the name, the process takes weeks to months, not a hundred years. Duck eggs are the most common choice, though chicken and quail eggs work too. The result is a striking, intensely flavored ingredient that’s been a staple in Chinese cuisine for centuries.
How Century Eggs Are Made
The traditional method involves coating raw eggs in a thick paste of wood ash, calcium oxide (quicklime), sea salt, and tea, then wrapping them in rice hulls. One classic recipe calls for roughly equal parts calcium oxide and oak ash mixed with a large amount of sea salt, all blended into a tea infusion to form a smooth mud. Each egg gets plastered in this mixture, and the coating slowly dries and hardens into a crust over several months.
Modern producers use a shortcut: soaking eggs in a solution of table salt, calcium hydroxide, and sodium carbonate for about 10 days, then sealing them in airtight containers for several more weeks of aging. The end result is similar to the traditional version, though some fans insist the slower method produces a more complex flavor.
What Happens Inside the Egg
The alkaline coating raises the pH inside the egg dramatically, creating conditions harsh enough to transform the proteins without any heat. As the alkali penetrates the shell, it breaks apart the protein molecules in the white and yolk, causing them to unfold, clump together, and cross-link into a gel. This is the same basic process that happens when you cook an egg, but driven by chemistry rather than temperature.
In the white, the proteins reorganize into a highly elastic gel, which is why the finished product has that bouncy, jelly-like texture instead of the firm bite of a boiled egg. The yolk undergoes a softer version of the same process, forming a low-hardness gel that ranges from creamy to slightly grainy depending on how long the egg was cured. Sulfur-containing amino acids in the proteins also break down during the process, releasing hydrogen sulfide and ammonia. These two compounds are responsible for the egg’s distinctive pungent smell.
The dramatic color changes come from the same chemical reactions. The dark amber-to-black color of the white and the deep green-gray of the yolk are byproducts of protein degradation and the interaction between hydrogen sulfide and minerals in the egg.
What They Taste and Smell Like
The smell hits first: a sharp, sulfurous, ammonia-like scent that can be off-putting if you’re not expecting it. The flavor is considerably more nuanced than the aroma suggests. The white is relatively mild with a slightly salty, mineral quality and a firm, gelatinous texture. The yolk is where the real character lives. It’s rich, deeply savory, and creamy, with an intensity sometimes compared to a very ripe cheese. Depending on the cure, the yolk can be almost liquid in the center or uniformly dense throughout.
If you’re trying one for the first time, steaming the egg for about five minutes before eating it firms up the yolk and mellows the flavor, making it a gentler introduction.
Nutrition Compared to Fresh Eggs
Century eggs are nutritionally similar to fresh duck eggs with a few notable differences. The protein content of a whole century egg sits around 13.1%, compared to 9.3 to 11.8% in a fresh duck egg, reflecting the concentration that happens as moisture slowly leaves during curing. Fat content drops slightly to about 10.7%, compared to 11.4 to 13.5% in fresh eggs.
The curing process also lowers cholesterol and phospholipid levels in the yolk compared to both fresh and salt-cured duck eggs. Mineral content, on the other hand, increases substantially during preservation. The sodium content is significantly higher than a fresh egg due to the salt in the curing mixture, which is worth keeping in mind if you’re watching your salt intake.
Common Ways to Eat Them
Century eggs are almost always eaten as an ingredient or accompaniment rather than on their own. The two most iconic preparations are congee (rice porridge) with century egg and shredded pork, and century egg with silken tofu. The congee is a comfort food across China and much of Southeast Asia: the egg’s richness dissolves into the mild, starchy porridge and gives it a deep umami backbone. The tofu dish is a cold appetizer popular in Taiwan and mainland China. Cubes of silken tofu are surrounded by chopped century egg and drizzled with a sauce of soy, sesame oil, garlic, and chili. The cool, neutral tofu balances the egg’s intensity perfectly.
You’ll also find century eggs sliced into wedges and served alongside pickled ginger as a simple appetizer, stirred into stir-fried vegetables, or added to hot pot. They pair well with anything that benefits from a punch of salty, funky richness.
Safety and the Lead Question
Historically, some producers added lead oxide to the curing mixture because it sped up the process and improved the surface appearance of the finished egg. This practice raised legitimate health concerns, and lead is not authorized for use as a food additive by the FDA or by Chinese food safety authorities. Modern commercial century eggs use zinc oxide instead when any metallic compound is included at all, and reputable brands are labeled as lead-free. If you’re buying century eggs at an Asian grocery store in the U.S., Canada, or Europe, the products on shelves have generally passed import inspections. Checking for a “lead-free” label (often printed in both Chinese and English) adds an extra layer of reassurance.
Storage and Shelf Life
Unopened century eggs with their curing coating or vacuum-sealed packaging intact can last for several months at room temperature. The high pH and salt content create an environment that’s inhospitable to most bacteria, which is the whole point of the preservation method. Once you peel them, treat them like any other cooked egg: refrigerate and eat within a day or two. Most packages include a production date and storage guidance, so check the label for specifics, as shelf life varies depending on whether the egg was made using the traditional clay method or the modern soaking technique.