Choy sum, along with bok choy and gai lan, is one of the most common Asian vegetables available in the west. It is a member of the brassica, or cabbage family, but this is a totally different vegetable to the common cabbage.
Caixin in Mandarin or choy sum in Cantonese translates as cabbage heart. The plant - Brassica chinesis v. parachinesis is an autumn to winter crop which grows to a height of 50 cm. It has pale green convex stems and deep green leaves, which grow to a length of between 15 and 20 cm. Choy sum leaves are more delicate than most other Asian greens, so care must be taken not to overcook them. They are slightly similar to bok choy leaves, just a little longer. Unlike other members of the Asian cabbage family, choy sum is often picked while flowering, hence its other common name, flowering green. The flowers grow at the point where leaf meets stem and are tiny, yet attractive yellow blooms.
Choy sum's venture into western kitchens was slowed by the plants attractive appearance. For many years the plant was grown as an ornamental in the west, with gardeners not realizing the tasty harvest that was at hand.
In cookery, choy sum has two distinct textures to lend a dish. The leaves are quite delicate, with a mild flavour resembling spinach. The stems add a whole new texture dynamic, with their thick yet lightly crunchy stems. Choy sum is a perfect ingredient in stir fried dishes as the leafy green crunch plays a nice counterpoint to any rich ingredients, such as meat and poultry. It also makes a sensational basis for a vegetarian stir fry.
Most Asian greens are grown in small local market gardens, rather than huge farms. Chinese farmers often eschew chemical pesticides, using white oil instead to repel insects. It still pays to wash choy sum and other Asian greens well once you get the home from the market.
Because of the different textures that choy sum provides, delicate leaf and crunchy stem, it is imporatant to prepare the vegetable carefully, adding the stem first, then the leaf later in dish. Slice the stems away from the leaves. Cut the stems into manageable lengths, around 5 cm, then set aside. Cut the leaves in halves and keep separate from the stems.
When stir frying, add the stems first and cook for 2-3 minutes or until tender. Add the leaves and just let them wilt. This should only take 30 or so seconds.