Century Egg

Food · Animal Foods · Poultry & Eggs

Connected to · 1

food source · 1

Choline
A century egg is a duck egg cured with alkali and salt. Curing neither adds nor removes fat, so the choline in the yolk largely remains. It suits an occasional side dish, one egg at a time, and the number to watch is sodium.
Mechanism · 2
Mechanism · What alkaline curing changes
Minerals are elements: curing can change what they are bound to but cannot make them vanish. Vitamins are molecules, and once alkali breaks their structure they stop working, so curing can only hold vitamins steady or lower them, never raise them. Choline sits in the yolk mainly as phospholipid, and the alkali does not carry it out of the yolk, so a century egg is still a source of choline.
Numbers · One egg and its sodium
Century egg itself is not in the USDA food-composition database, so read its numbers from the raw material, fresh duck egg: 12.8 g of protein and 13.8 g of fat per 100 g. One century egg gives about 50–60 g you can eat, which suits an occasional side dish, not several a day. Sodium is the number to watch: the alkali that sets the egg white into a gel is sodium hydroxide, and the sodium soaks into the egg along with it. The translucent gel needs the alkali to get in, so a low-sodium century egg is hard to make.

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What century egg is · a chemically transformed duck egg

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A century egg is a duck egg that strong alkali has reworked over several weeks: the alkali sets the white into a translucent gel and turns the yolk dark green, with no heating and no preservative. The chapter on how alkali turns an egg into a century egg walks through the chemistry.

The eggs soak for weeks to months in a mix of sodium hydroxide (NaOH), salt, tea, and other ingredients, and the surface often grows crystal patterns that look like pine branches. Century-egg congee with lean pork, century egg with ginger, and century egg with tofu are common ways to eat it.

Traditional curing mixes once used lead-containing metal salts; modern regulated production mostly uses copper or zinc instead. What really needs managing day to day is its sodium.

Two century-egg halves with translucent amber-brown white around grey-green yolk. — A CLOSER LOOK
The white can set without cooking
Alkaline curing changes colour and texture; this cannot establish sodium content or food safety.

Educational content, not medical advice — consult a clinician.

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