Every year the lady who cares for my octogenarian grandparents presents to them a bag of mei gan cai (also called mei cai), or dried and pickled mustard greens. She hails from a small village in Zhejiang Province just outside of Shanghai, where the preserved vegetables are a specialty. Happily, the product is now widely available in Chinese markets in the United States.
A number of different varieties of mustard greens and cabbage may be used in the making; the process is long and complicated. The vegetables, once harvested, are sun-dried, salted, fermented, steamed, and finally, dried again, yielding clumps of reddish-brown to dark brown twigs. Though the entire process takes several weeks, the preserved mustard greens can be kept for years without deterioration.
Given the various stages of drying, brining, and fermenting, mei gan cai tastes uniquely savory and complex: salty and wine-y, with an herbaceous and pungent flavor. Like olive, anchovies, sun-dried tomatoes,or just about anything that's been pickled, brined, or in some way preserved, mei cai is a handy ingredient to have in your pantry. Adding just a handful of mei cai to a braised dish gives the entire dish a more complex tone because the flavor profile of vegetables, intensified by their production, infuses a lot of umami into meat, tofu, or just about any braising ingredient.
Mei cai is a prized ingredient in the common red-braised dishes in central and southern China; the briny vegetables add a savory note to the sweet soy sauce-based braises. To use mei cai, simply rehydrate a few handfuls of the vegetable in water before adding them to your braise. Look for the product in the dried goods aisles of your Chinese market.