The Complete Handbook of On Choy

Chapter 1: Understanding On Choy

On choy is not bok choy. That is the single most useful fact about it, and the one that is most often wrong in both print and online references. Bok choy (or pak choi) forms a compact rosette of broad, spoon-shaped leaves on fleshy white or green stalks, and it is harvested in a vegetative state. On choy belongs to the same species, Brassica rapa, but it is grown primarily for its flowering stems, which are harvested when the flower buds are still tightly bunched and yellow. The leaves are narrower and more elongated, the stems are thin and pencil-like, and the entire plant—stem, leaf, and immature flower heads—is eaten. This distinction is not pedantry. It changes how the vegetable is grown, how it is graded, how quickly it deteriorates after harvest, and, most importantly, what you can do with it in the kitchen.

You will hear many names for it in a market setting. The Cantonese term choy sum literally means "vegetable heart," and it refers to the tender central shoot harvested for eating. In mainland China, the same crop is often sold as you cai (oil vegetable) because the seeds are also pressed for rapeseed oil. Western suppliers may label it "Chinese flowering cabbage," "yu choy," or, confusingly, simply "bok choy," even when the product in the crate is plainly flowering. The botanical identifier is Brassica rapa subsp. chinensis var. parachinensis, which separates it from the regular bok choy variety. When ordering