Dairy & Eggs

Century Egg

Preserved duck or chicken egg with translucent dark jelly white and creamy dark yolk, served in congee and salads.

Century egg (pidan) is a Chinese preserved egg cured for weeks in an alkaline mixture of clay, ash, salt, and lime. The process turns the white into a translucent amber-to-black jelly and the yolk into a creamy, dark green-grey center with a rich, savory, faintly sulfurous flavor. It is eaten sliced over congee, with pickled ginger, or in cold tofu dishes.

Century Egg is a preserved egg achieved through alkaline curing—a process that fundamentally transforms the chemistry and texture of duck, chicken, or quail eggs. The eggs are packed in a mixture of quicklime, sodium carbonate, and salt (or sometimes tea ash and rice hulls), where the high-alkaline environment (pH 9–12) denatures proteins and triggers sulfur-iron reactions within the yolk. The result is a striking visual transformation: the albumin becomes a translucent, jelly-like dark substance, while the yolk develops a creamy, dark green-gray center with a custard-like consistency. Far from spoiled, this is controlled enzymatic modification at work. The flavor profile is distinctive—umami-rich, faintly nutty, and earthy with subtle sulfidic notes that become milder when properly prepared. Century eggs have been produced in China since the Ming Dynasty (16th century), originating in Hunan province, and remain a cornerstone of dim sum, congee bowls, and cold appetizers across East and Southeast Asia. The pine-needle-like crystalline patterns sometimes visible on the shell interior are precipitated magnesium ammonium phosphate (struvite)—a reliable indicator of proper, gradual curing and quality.

Measured in: piece
Storage: Pantry

Allergens

Egg

Types & varieties

Songhua Dan (松花蛋)

Premium grade; named for distinctive pine-needle-like magnesium ammonium phosphate crystals on the shell surface

Duck Egg Century Egg

Traditional and most common; larger, richer flavor from higher fat content

Chicken Egg Century Egg

Smaller, milder; less traditional but more accessible

Quail Egg Century Egg

Miniature specialty; often served whole as garnish

Wet-cured (brine method)

Modern industrial method; eggs soaked in saline-alkaline solution rather than coated

Dry-cured (traditional)

Coated in a paste of quicklime, ash, and salt; longer aging, more complex flavor

The Chemistry of Transformation

The dramatic visual change in century eggs is pure chemistry. Alkaline curing raises the egg's pH from around 7 to 9–12, causing calcium hydroxide and sodium carbonate to penetrate the shell and alter the protein structure. Albumin proteins denature and reorganize into a translucent gel that lets light pass through, creating the characteristic 'jelly white' appearance. Within the yolk, sulfur compounds from degraded proteins combine with iron (present in egg whites) to form iron sulfide, producing the dark green-gray coloration. This is the same reaction that creates greenish-gray rings around hard-boiled egg yolks. The process also generates ammonia compounds, which contribute to the distinctive aroma. These chemical changes are intentional and safe—properly cured century eggs are not spoiled, merely profoundly transformed.

Look for fern-like crystalline patterns on shell interior—this struvite indicates proper curing
The dark yolk color comes from iron-sulfur reactions, not spoilage
Higher pH extends shelf life by inhibiting microbial growth

Selecting Quality Century Eggs

Choose heavy eggs with clean, uncracked shells. When held up to light, quality eggs should show a clear demarcation between the translucent albumin and the darker yolk center. The pine-needle crystalline patterns (struvite) on premium grades like Songhua Dan indicate slow, controlled curing rather than rapid industrial processing. Avoid any eggs with bulging ends, off odors, or shell cracks—while the alkaline curing inhibits most pathogens, compromised shells can allow contamination. Some industrial producers add copper sulfate as a color fixative to achieve a deeper black appearance; this is safe but worth noting if you prefer minimal additives.

Heavier eggs indicate better water retention and proper gel texture
Clean shells without residue or cracks are essential
Pine-needle crystal patterns signal premium slow-cured quality

Common uses

Sliced and served as cold appetizer with ginger strips and light soy sauceChopped into congee (jook) as a savory garnish for breakfast or comfort foodCubed in cold tofu salad or mixed vegetable salads for textural contrastServed alongside congee and pickled vegetables for traditional dim sum breakfastLayered in clay pot rice (煲仔飯) in final minutes of cooking for richnessChopped into steamed egg custard or silken tofu dishes for added depthQuartered as garnish for pork or duck congee—the most iconic preparationServed with fried rice or noodle dishes for breakfast or casual mealsSliced thin as garnish for hot pot or steamboat broths at table

Tips & pitfalls

Select eggs showing distinct crystalline patterns on shell; heavier eggs with clean shells indicate quality
Rinse under cold water before peeling to remove alkaline coating and improve texture
Bring to room temperature before serving; cold temperatures suppress aromatic compounds
Blanch peeled eggs in boiling water for 30 seconds to mellow strong alkaline taste if desired
Check ingredient labels for copper sulfate (some industrial processes use it as a color fixative)
Avoid eggs with cracked shells, off odors, or excessively bulging ends
If opening a package of individually wrapped eggs, consume all within 2 weeks for best quality
To minimize sulfur smell, store away from other strong-smelling foods
When slicing, use a knife dipped in water or lightly oiled to prevent sticking

Nutrition

143kcal

Energy

598 kJ · per 100 g

Where the calories come from

Protein 36%Carbs 2%Fat 62%

Protein

12.6g

25% DV

Carbs

0.7g

0% DV

Fat

9.5g

12% DV

Fiber

0% DV

Sugars

0.4g

of which

Sodium

142mg

6% DV

Notable micronutrients

Selenium56% DV

Vitamin B1237% DV

Riboflavin (B2)35% DV

Vitamin A18% DV

Phosphorus16% DV

Folate12% DV

Source · USDA FoodData Central · approx. Egg, whole, raw, fresh

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Good to know

Also called: Pidan (皮蛋), Songhuajiang (松花蛋), Thousand-Year Egg
Origin: China; Ming Dynasty, circa 16th century, Hunan province
Primary egg type: Duck egg (traditional); also chicken and quail
Processing agents: Quicklime (calcium oxide), sodium carbonate, salt, sometimes rice hulls or tea ash
Key chemical change: High pH (9–12) denatures proteins, producing translucent albumin and sulfur-iron reactions in yolk
Processing time: 2 weeks to 3 months (not 100 years)
Shelf life (unopened): 6–12 months at room temperature or refrigerated
Shelf life (opened/peeled): 1–2 weeks refrigerated
pH: 9–12 (strongly alkaline)
Season: Available year-round; peak production in winter for spring availability

Substitutes

Tea Egg (茶叶蛋) — Marinated boiled egg with soy and tea; different flavor profile but similar savory egg garnish for congee or rice dishes
Salt-cured Egg Yolk — Duck yolk cured in salt; provides rich, savory element but lacks the jelly texture and complex alkaline flavor
Soft-poached Egg — Useful for texture contrast in congee or grain bowls; not a flavor substitute but workable for similar plating presentations

Pairs with

Fresh ginger Soy sauce Sesame oilScallions and cilantroRice congeeSilken or soft tofuChili oil or fresh chiliesShaoxing rice wine

Also called

皮蛋 · Preserved Egg · Pidan · Thousand-Year Egg