Food · Meat & Seafood · 禽蛋
Century Egg
强碱腌制的化学: 蛋白凝胶、松花金属离子、蛋黄硫化铁 · 铅说法用机制拆: 需要的是金属离子不是铅 · 钠才是日常该管的量
Story path
- 1What century egg is · a chemically transformed duck eggWhat century egg is · a chemically transformed duck egg
- 2Macros · high fat and protein; sodium is the headlineMacros · high fat and protein; sodium is the headline
- 3Fat & cholesterol · the yolk concentrates bothFat & cholesterol · the yolk concentrates both
- 4Rich in what · the yolk's nutrients surviveRich in what · the yolk's nutrients survive
- 5What it lacks · how to pairWhat it lacks · how to pair
- 6Key knowledge · how alkali turns an egg into a century eggKey knowledge · how alkali turns an egg into a century egg
- 7How to choose · serve · how muchHow to choose · serve · how much
- 8Debunking · lead and nitrite misreadsDebunking · lead and nitrite misreads
Chapter 1
What century egg is · a chemically transformed duck egg
What century egg is · a chemically transformed duck egg
Century egg (preserved egg, pidan) is a duck egg transformed by alkali curing: a solution of sodium hydroxide (NaOH), salt and tea soaks the eggs for weeks to months until the white becomes a dark translucent gel and the yolk turns ink-green to ochre, often flowering with crystalline 'pine' patterns.
It is one of the most chemically expressive foods in Chinese cuisine — the process is reshaping protein with alkali, not adding preservatives. Century-egg congee, ginger century egg, and century-egg tofu are common uses.
The mechanism core is the curing chemistry — how alkali reshapes white and yolk (special-knowledge). The lead claim is handled only in debunking via mechanism: traditional mixes once used a lead-based metal source; modern mixes use copper or zinc for the same crystals and gel.
Nutritionally, century egg is built on the duck egg (~185 kcal, 12-13 g protein, 14 g fat per 100 g); curing hydrolyzes protein but total protein survives, while sodium rises clearly from the curing salt.
It is one of the most chemically expressive foods in Chinese cuisine — the process is reshaping protein with alkali, not adding preservatives. Century-egg congee, ginger century egg, and century-egg tofu are common uses.
The mechanism core is the curing chemistry — how alkali reshapes white and yolk (special-knowledge). The lead claim is handled only in debunking via mechanism: traditional mixes once used a lead-based metal source; modern mixes use copper or zinc for the same crystals and gel.
Nutritionally, century egg is built on the duck egg (~185 kcal, 12-13 g protein, 14 g fat per 100 g); curing hydrolyzes protein but total protein survives, while sodium rises clearly from the curing salt.
Chapter 2
Macros · high fat and protein; sodium is the headline
Macros · high fat and protein; sodium is the headline
Start with the data question, because it sets how far to trust every number below: century egg itself is not in the USDA database — what the authoritative tables hold is its raw material, the fresh duck egg (per 100 g: 185 kcal, 12.8 g protein, 13.8 g fat, 884 mg cholesterol, 146 mg sodium). So read century egg's nutrition as the duck egg's baseline plus the directional changes curing makes; for exact figures, read the panel on the box in your hand.
A century egg (~60-70 g with shell) yields ~50-60 g edible. What curing does to that baseline:
Calories and fat: essentially the duck egg's — alkali curing adds no oil and removes no fat; fat stays in the yolkProtein: alkali and curing-period proteases hydrolyze large proteins into peptides and amino acids; total protein survives but digests more easily, and brings savoury tasteCarbohydrate: very lowSodium: clearly above fresh eggs — curing salt migrates into the egg. This is the metric that actually matters, and the one number you genuinely must read off the package
Versus chicken eggs (~155 kcal, 13 g protein per 100 g), century egg is similar in calories and fat, and clearly saltier. It is a sometimes dish for a plate, not a half-dozen breakfast food.
For eggs systematically, dive to eggs.
A century egg (~60-70 g with shell) yields ~50-60 g edible. What curing does to that baseline:
Calories and fat: essentially the duck egg's — alkali curing adds no oil and removes no fat; fat stays in the yolkProtein: alkali and curing-period proteases hydrolyze large proteins into peptides and amino acids; total protein survives but digests more easily, and brings savoury tasteCarbohydrate: very lowSodium: clearly above fresh eggs — curing salt migrates into the egg. This is the metric that actually matters, and the one number you genuinely must read off the package
Versus chicken eggs (~155 kcal, 13 g protein per 100 g), century egg is similar in calories and fat, and clearly saltier. It is a sometimes dish for a plate, not a half-dozen breakfast food.
For eggs systematically, dive to eggs.
Chapter 3
Fat & cholesterol · the yolk concentrates both
Fat & cholesterol · the yolk concentrates both
Century egg's fat is almost all in the yolk, inheriting the duck egg's baseline (fresh duck egg ~13.8 g/100 g, of which ~3.7 g saturated) — a mix of saturated and unsaturated like duck or chicken egg yolk; curing invents no special fat.
Cholesterol is the number egg foods cannot avoid: fresh duck eggs are high (~884 mg/100 g, measured by USDA) and century egg inherits that. But repeat the conclusion eggs already dismantled: for most people, dietary cholesterol moves blood lipids less than total saturated fat, and the body compensates by down-regulating its own synthesis; yolks are not a risk food for most.
What deserves attention remains sodium and frequency: century egg plus its salty dipping sauces can blow a meal's sodium budget; high salt is the variable actually associated with cardiovascular risk (see salt).
For the full dietary-cholesterol argument, dive to eggs and shrimp; for fat structure, dive to fats-omega-3.
Cholesterol is the number egg foods cannot avoid: fresh duck eggs are high (~884 mg/100 g, measured by USDA) and century egg inherits that. But repeat the conclusion eggs already dismantled: for most people, dietary cholesterol moves blood lipids less than total saturated fat, and the body compensates by down-regulating its own synthesis; yolks are not a risk food for most.
What deserves attention remains sodium and frequency: century egg plus its salty dipping sauces can blow a meal's sodium budget; high salt is the variable actually associated with cardiovascular risk (see salt).
For the full dietary-cholesterol argument, dive to eggs and shrimp; for fat structure, dive to fats-omega-3.
Chapter 4
Rich in what · the yolk's nutrients survive
Rich in what · the yolk's nutrients survive
Curing changes century egg's texture and flavor, but most yolk micronutrients survive:
Complete protein: hydrolyzed, easier to digest, full amino-acid profileCholine (choline): yolk is a quality choline source for nerve and liver metabolismLecithin and fat-soluble vitamins (A, D, E, K): all live in the yolkVitamin B12 (vitamin-b12): eggs are a B12 sourcePhosphorus, selenium, iron (non-heme): moderate
To be honest: century egg is not a density champion; its value ordering is flavor > convenience > nutrition. The congee's lean pork supplies protein and the rice supplies carbohydrate; century egg contributes the egg base.
There is no 'curing made it more nutritious' magic — alkali treatment does limited harm to minerals but adds no vitamins. Do not believe 'century egg is more nutritious' marketing (presenting curing as fortification, same genre as plant-milk pitches).
Complete protein: hydrolyzed, easier to digest, full amino-acid profileCholine (choline): yolk is a quality choline source for nerve and liver metabolismLecithin and fat-soluble vitamins (A, D, E, K): all live in the yolkVitamin B12 (vitamin-b12): eggs are a B12 sourcePhosphorus, selenium, iron (non-heme): moderate
To be honest: century egg is not a density champion; its value ordering is flavor > convenience > nutrition. The congee's lean pork supplies protein and the rice supplies carbohydrate; century egg contributes the egg base.
There is no 'curing made it more nutritious' magic — alkali treatment does limited harm to minerals but adds no vitamins. Do not believe 'century egg is more nutritious' marketing (presenting curing as fortification, same genre as plant-milk pitches).
Chapter 5
What it lacks · how to pair
What it lacks · how to pair
What century egg lacks is everything mild and fibrous beyond the sodium: high-sodium, high-fat, no fiber, no vitamin C — a plate alone can max out a meal's sodium.
Practical pairings:
Congee or whole grains: dilute the sodium, add carbohydrateDark leafy greens or tofu: add fiber, potassium and calcium, balancing sodiumGo easy on extra seasoning: the soy sauce and salt in ginger century egg and century-egg tofu are on you — the egg is already salty
Vitamin-C angle: add tomato or greens to the meal; vitamin C and potassium push back against a high-sodium load (see salt and potassium-sodium).
In one line: century egg is the flavor lead and the nutritional supporting role — it makes congee and tofu taste great; it is not a daily nutritional requirement.
Practical pairings:
Congee or whole grains: dilute the sodium, add carbohydrateDark leafy greens or tofu: add fiber, potassium and calcium, balancing sodiumGo easy on extra seasoning: the soy sauce and salt in ginger century egg and century-egg tofu are on you — the egg is already salty
Vitamin-C angle: add tomato or greens to the meal; vitamin C and potassium push back against a high-sodium load (see salt and potassium-sodium).
In one line: century egg is the flavor lead and the nutritional supporting role — it makes congee and tofu taste great; it is not a daily nutritional requirement.
Chapter 6
Key knowledge · how alkali turns an egg into a century egg
Key knowledge · how alkali turns an egg into a century egg
The scene worth getting right — the curing chemistry:
1. Alkali gels the white: sodium hydroxide pushes the egg's pH from ~7.6 to 9-12, a pH at which hydrogen and disulfide bonds in egg protein break and re-crosslink, turning the transparent liquid white into a translucent gel — that is where 'jelly-like white' comes from. Proteases are more active at this pH, splitting big proteins into peptides and amino acids — which is why century egg tastes savory (amino acids) and digests easily.
2. The 'pine flowers': the usual account is that amino acids released by protein hydrolysis crystallize under alkaline conditions, growing branching patterns on the white's surface; metal salts in the curing mix (traditionally lead-bearing, today copper or zinc) participate in gel formation and crystallization — which is why traditional recipes could not skip the metal: it is not just decoration, it also affects gel texture.
3. The green yolk: iron in the yolk reacts with hydrogen sulfide from protein breakdown to form iron sulfide (FeS), tinting the yolk ink-green/gray — a reaction product, not spoilage. The green ring in a hard-boiled egg left too long is the same reaction.
This chemistry explains every 'weird' look of century egg — jelly white, pine flowers, green yolk — all products of alkali + time + metal ions: a repeatable, controlled food process, not 'gone bad'.
With this chemistry in hand, the lead claim is easy to follow: the process needs metal ions for flowers and gel, not lead specifically; traditional mixes once used lead oxide, modern ones use copper or zinc — lead is dangerous because absorbed lead enters blood and harms nerves and blood-forming tissue.
1. Alkali gels the white: sodium hydroxide pushes the egg's pH from ~7.6 to 9-12, a pH at which hydrogen and disulfide bonds in egg protein break and re-crosslink, turning the transparent liquid white into a translucent gel — that is where 'jelly-like white' comes from. Proteases are more active at this pH, splitting big proteins into peptides and amino acids — which is why century egg tastes savory (amino acids) and digests easily.
2. The 'pine flowers': the usual account is that amino acids released by protein hydrolysis crystallize under alkaline conditions, growing branching patterns on the white's surface; metal salts in the curing mix (traditionally lead-bearing, today copper or zinc) participate in gel formation and crystallization — which is why traditional recipes could not skip the metal: it is not just decoration, it also affects gel texture.
3. The green yolk: iron in the yolk reacts with hydrogen sulfide from protein breakdown to form iron sulfide (FeS), tinting the yolk ink-green/gray — a reaction product, not spoilage. The green ring in a hard-boiled egg left too long is the same reaction.
This chemistry explains every 'weird' look of century egg — jelly white, pine flowers, green yolk — all products of alkali + time + metal ions: a repeatable, controlled food process, not 'gone bad'.
With this chemistry in hand, the lead claim is easy to follow: the process needs metal ions for flowers and gel, not lead specifically; traditional mixes once used lead oxide, modern ones use copper or zinc — lead is dangerous because absorbed lead enters blood and harms nerves and blood-forming tissue.
Chapter 7
How to choose · serve · how much
How to choose · serve · how much
To the market and the table:
Choosing: buy regulated brands with production licenses (name, standard and shelf-life on the package). Shell intact, firm on tap; the peeled white is a translucent gel with clear flowers and no off-odor. A 'lead-free process' label signals modern processing.
Serving: century egg is a ready-to-eat egg product — peel and eat; in congee or with tofu, add it after the heat is off (it needs no cooking; reheating toughens the white). A soft center is normal, not undercooked — century egg's 'doneness' comes from curing, unlike a raw egg.
How much: century egg's sodium is the hard metric — about one egg per sitting (~50-60 g edible), not a plate of several; people with hypertension or kidney disease should be more restrained, per their doctor.
Who should be careful: sodium-sensitive people (hypertension, kidney disease) and anyone allergic to eggs — century egg shares the egg's allergenicity, so egg-allergic people may react to it too. Consult a doctor for personal medical questions.
Choosing: buy regulated brands with production licenses (name, standard and shelf-life on the package). Shell intact, firm on tap; the peeled white is a translucent gel with clear flowers and no off-odor. A 'lead-free process' label signals modern processing.
Serving: century egg is a ready-to-eat egg product — peel and eat; in congee or with tofu, add it after the heat is off (it needs no cooking; reheating toughens the white). A soft center is normal, not undercooked — century egg's 'doneness' comes from curing, unlike a raw egg.
How much: century egg's sodium is the hard metric — about one egg per sitting (~50-60 g edible), not a plate of several; people with hypertension or kidney disease should be more restrained, per their doctor.
Who should be careful: sodium-sensitive people (hypertension, kidney disease) and anyone allergic to eggs — century egg shares the egg's allergenicity, so egg-allergic people may react to it too. Consult a doctor for personal medical questions.
Chapter 8
Debunking · lead and nitrite misreads
Debunking · lead and nitrite misreads
The most famous claim — century egg contains lead; do not eat it — comes apart with the chemistry in special-knowledge:
Body risk: absorbed lead enters blood and harms nerves and blood-forming tissue — real toxicity, not scare talk.
What the process needs: flowers and gel need metal ions, not lead itself. Traditional mixes once used lead oxide as that metal source, so lead exposure was a real problem then; modern mixes use copper or zinc for the same crystals and gel, and regulated products should not rely on lead.
Fake test: 'darker = more lead' is false — the green comes from iron sulfide and flower chemistry, unrelated to lead. Choose by reputable source and label, not shade.
Related: 'cured food, so high nitrite and cancer' — century egg is alkali-cured, not nitrate/nitrite-cured (that is the cured-meat route; see leftovers-nitrite). Do not conflate.
Conclusion: fear the lead-exposure path, not the word 'century egg'; for modern regulated products the real long-term watch-item is sodium, not the lead myth.
Body risk: absorbed lead enters blood and harms nerves and blood-forming tissue — real toxicity, not scare talk.
What the process needs: flowers and gel need metal ions, not lead itself. Traditional mixes once used lead oxide as that metal source, so lead exposure was a real problem then; modern mixes use copper or zinc for the same crystals and gel, and regulated products should not rely on lead.
Fake test: 'darker = more lead' is false — the green comes from iron sulfide and flower chemistry, unrelated to lead. Choose by reputable source and label, not shade.
Related: 'cured food, so high nitrite and cancer' — century egg is alkali-cured, not nitrate/nitrite-cured (that is the cured-meat route; see leftovers-nitrite). Do not conflate.
Conclusion: fear the lead-exposure path, not the word 'century egg'; for modern regulated products the real long-term watch-item is sodium, not the lead myth.