A century egg (pidan) is a duck egg preserved for weeks or months in an alkaline cure of clay, ash, salt and lime until it transforms utterly: the white sets into a firm, translucent dark-amber jelly and the yolk turns creamy grey-green with a soft, oozy centre. The alkali breaks down the egg's proteins and fats without heat, giving a rich, savoury, faintly sulfurous and ammoniacal flavour prized across China. Neither raw nor cooked but chemically "aged," it is a cornerstone of Chinese congee, tofu appetisers and cold platters.