Mei cai (梅菜, also known as meicai, dried plum vegetables, or Shaoxing preserved vegetables) are the sun-dried, salted, and lightly fermented mustard greens that are one of the most important preserved ingredients in Jiangnan and Cantonese cooking. Made in Shaoxing by salting fresh mustard greens (or amaranth), allowing them to ferment briefly, then pressing and sun-drying them until shrivelled and intensely concentrated. The resulting mei cai has a complex savouriness with sweet, slightly fermented notes and a concentrated umami depth far beyond fresh vegetables. They are the essential partner to Dongpo pork (mei cai kou rou) and are used in clay pot preparations, steamed pork, and as a filling for baozi.
Using mei cai in cooking: Before use, soak dried mei cai in cold water for 30 minutes to 1 hour. Rinse thoroughly — some brands are very salty. Taste the soaked mei cai; if still very salty, soak longer. Squeeze out excess water. Chop roughly if desired. Mei cai kou rou (梅菜扣肉, braised pork belly with preserved vegetables): The classic preparation. Layer sliced, braised pork belly in a bowl with a layer of mei cai below. Steam for 1 hour until everything is tender and the flavours have completely merged. Invert onto a serving platter. The pork belly and mei cai will be melted together into an intensely savoury preparation. Substitution: Suan cai (Chinese fermented cabbage, northern style) or zha cai can substitute in some applications but not in mei cai kou rou where the specific Shaoxing dried mustard green flavour is central.
Fuchsia Dunlop, Land of Fish and Rice (2016); Fuchsia Dunlop, Every Grain of Rice (2012)