Suan cai (酸菜, literally sour vegetable) is the traditional lacto-fermented napa cabbage of northern China — particularly Dongbei (northeast China: Liaoning, Jilin, Heilongjiang provinces) — made by salting and fermenting whole or quartered napa cabbage heads in ceramic crocks over the winter months. The fermentation produces a pleasantly sour, slightly tangy preserved cabbage that is the foundation of several northern Chinese preparations: suan cai hot pot (酸菜锅子), suan cai dumplings (酸菜饺子), and the iconic northeastern dish of suan cai with pork (猪肉酸菜). It is the Chinese equivalent of German sauerkraut or Korean kimchi.
Fermentation method: Wash napa cabbage thoroughly. Salt generously (approximately 2% of the cabbage weight in salt). Layer in a ceramic crock with salt between layers. Press with a weight to keep the cabbage submerged in the brine that forms as the salt draws moisture from the cabbage. Allow to ferment at room temperature for 3-5 days (in summer) or 10-14 days (in winter — the cold-climate traditional method). The longer fermentation at lower temperatures produces a more complex, nuanced flavour. Suan cai dumplings: Suan cai provides a different texture and flavour base from fresh cabbage in dumpling fillings — the fermented acidity balances the richness of pork. The suan cai must be squeezed very dry before use as a filling (it contains a great deal of liquid from the fermentation brine).
Fuchsia Dunlop, Every Grain of Rice (2012)