What Is a Century Egg?

A century egg (皮蛋, Cantonese pei daan, Mandarin pi dan) is a Chinese duck or chicken egg preserved through alkaline fermentation in ash, salt, tea, and clay for several weeks to months. The white transforms into a dark amber gel, the yolk into a creamy gray paste with a distinct umami-sulfurous aroma. At China Restaurant Yung Frankfurt, we have served this Cantonese classic as an appetizer since 1988.

Etymology and Name Origin

The Chinese name 皮蛋 (pi dan) literally means „leather egg“ — a reference to the leathery, glossy surface of the cured egg. In Cantonese it is pei daan (Jyutping pei4 daan2), in Mandarin pi dan (Pinyin pí dàn). English readers encounter three common labels — century egg, thousand-year egg, and hundred-year egg — all metaphorical, none literal: production takes four weeks to three months depending on method.

The tradition originated in the late Ming dynasty (sixteenth century) in Hunan province in southern China. One legend tells of a farmer who discovered duck eggs forgotten in a slaked-lime pit and noticed they had developed a refined flavor. Wikipedia: Century egg · Wikidata: Q900814.

How Century Eggs Are Made

The classical method (Mandarin cǎo huī fa, „ash method“) uses an alkaline coating of wood ash, calcium oxide (quicklime), salt, black tea, and clay — sometimes mixed with rice husks as a stabilizer. Raw duck or chicken eggs are encased in this paste, rolled in rice husks, and stored cool and dry for four to six weeks.

Two transformations occur during fermentation. First, hydroxide ions migrate through the eggshell and denature albumin (the white) into a firm, translucent gel. Second, sulfur-bearing amino acids react in the alkaline environment to form hydrogen sulfide — the source of the egg’s signature aroma. The yolk becomes a dark gray-green paste with a creamy texture, comparable to a strongly aged cheese.

The industrial method shortens production to ten to fourteen days using a sodium-hydroxide soak. Traditional and industrial eggs differ in flavor depth — at China Restaurant Yung we use only traditionally ash-cured eggs.

Taste and Texture

Century eggs taste intensely umami, gently sulfurous, and creamy-savory — a flavor profile with no direct Western equivalent. The closest comparison is an aged blue cheese (Roquefort, Gorgonzola) or a long-aged truffle: the sulfur note is related to fermented soybean products like doubanjiang or miso.

Texturally, the egg is bipartite: the white is firm, translucent, amber, with a slightly springy bite; the yolk is soft, creamy, almost paste-like, and dissolves on the palate. The contrast — firm shell with a melting core — is one of the most distinctive sensory experiences in Cantonese cuisine.

Culinary Uses

Cantonese and Hunan kitchens use century eggs in four classical preparations:

1. Pi Dan Shou Rou Zhou (皮蛋瘦肉粥) — congee (rice porridge) with lean pork and diced century egg; arguably the most beloved Cantonese breakfast dish
2. Liang Ban Pi Dan (涼拌皮蛋) — cold salad of century eggs, fresh tofu, scallions, and sesame oil
3. Pi Dan Doufu (皮蛋豆腐) — soft tofu topped with century-egg sauce, a vegetarian variant
4. Plain appetizer — quartered eggs served with pickled ginger and aged black soy sauce (our classic antipasti at China Restaurant Yung Frankfurt)

Outside China, century eggs appear in Vietnamese (hột vịt bắc thảo) and Thai (khai yiao maa) cuisine. In Western fine-dining, chefs increasingly use the egg as an unusual umami component alongside sashimi or as a glaze for grilled meats.

Allergens and Data Provenance

Century eggs contain only one declarable allergen — hen’s egg / duck egg (E) under the EU LMIV-14 framework (cross-mapped to FDA Top-9 in the United States). They contain no gluten, no dairy, no nuts. The hydrogen sulfide produced during fermentation is a natural reaction byproduct, not a regulated additive.

Allergen and additive data on this page come from our ChinaYung-Software (German site) — an AI pipeline for restaurant compliance, automatically cross-checking ingredients against the EU LMIV-14 allergens and 13 additive classes.

Frequently Asked Questions — Century Egg

Are century eggs really one hundred years old? — No. The name is a commercial translation. Curing takes four weeks to three months depending on the method used.

What do they taste like? — Intensely umami, gently sulfurous, creamy-savory. Comparable to aged blue cheese combined with the depth of well-cured truffle.

Are they raw or cooked? — Neither — they are chemically cooked through alkaline fermentation. Albumin is denatured (similar to hard-boiled egg white), but the process runs cold over several weeks.

Are they healthy? — Yes, in moderate quantities. They retain all nutrients of a hen’s egg plus elevated mineral concentrations from the alkaline cure. Because of the sodium content from the salt bed, people managing high blood pressure should consume them sparingly.

Why is the yolk dark green-gray? — Sulfur-bearing amino acids in the egg react in the alkaline environment to form hydrogen sulfide, which then reacts with iron compounds in the yolk to produce iron sulfide — hence the gray color. It is a natural chemical effect, not a sign of spoilage.

Are they vegetarian or vegan? — They are vegetarian (lacto-ovo). They are not vegan, as they remain an egg product.

How long do they keep? — Two to three months unshelled at room temperature; one to two days shelled in the refrigerator. Alkaline preservation prevents microbial growth.

At China Restaurant Yung Frankfurt

At China Restaurant Yung (Oeder Weg 32, Frankfurt), we serve century eggs as a classical Cantonese appetizer — quartered, paired with pickled ginger, scallions, and aged black rice vinegar. Related Knowledge entries: Mandarin Peel (陳皮) · Quail Egg (鵪鶉蛋) · Dim Sum hub.

Reservations: chinayung.de/en · Allergen-filtered menu: menu.chinayung.de.