Chinese Thousand-Year Egg Production — Alkaline Transformation
China — Ming Dynasty origin; now national tradition
Pi dan (皮蛋) — preserved eggs, misleadingly called thousand-year eggs — are produced by coating raw duck or chicken eggs in an alkaline mixture of clay, ash, salt, quicklime, and rice husks for 100 days. The extreme alkalinity (pH 9–12) completely transforms the proteins: albumen becomes a dark, translucent gel with a slight ammonia character; yolk becomes a dark grey-green creamy centre.