Products - Choi Sum (Brassica parachinensis)

Choi Sum (Brassica parachinensis) is a member of the Mustard family is also referred to as a flowering pak choy or choy sum. Its green leaves are juicy and tender. If allowed to mature and bolt, yellow flowers will shoot and the plant becomes sweeter and more succulent. The whole plant is edible.

Choi Sum is one of the most popular vegetables among the Chinese and is probably the most popular vegetable in Hong Kong. It is now also widely used in the western world.

The flowering shoots and younger leaves of Choi Sum are used in salads or stir-fried, lightly boiled or steamed and added to meat. Choi Sum is rich in carotene (pro-vitamin A), calcium and dietary fibre, it also provides potassium and folic acid.

The flavour itself can be described as midway between cabbage and spinach. Choi Sum tends to be blander and closer in taste to cabbage in younger leaves, and develops a little 'kick' in its older leaves. It is reputedly very nutritious, and in particular, is said to be rich in calcium.

Choi Sum is characterised by yellow flowers borne on slightly fleshy stems 0.5 to 1 cm in diameter and 15 to 20 cm long. The plant height varies from 20-30 cm. Leaves are either light or dark green and are oval or egg-shaped with slightly serrated margins. The flowering starts when there are about 7 - 8 leaves on the plant. The bulk of the root system is within a depth of 12 cm and is confined to a radius of 12 cm. The plant's average spread varies between 15 - 45 cm.

Choi Sum is considered to be a cool season crop preferring uniform conditions, moderate moisture levels and reasonable sunlight. When seasons are not too extreme, it can be grown all year round. The higher temperatures may result in thinner, tougher and less sweet shoots or may lead to bolting. Choi Sum is not frost tolerant, however, there is a purple-flowered variety that can withstand temperatures below 0C. The optimum temperature for minimum time to harvest can be between 15C and 25C.

Choi Sum is usually grown at plant spacings varying from 2.5 - 20 cm and row spacings of between 7 - 30 cm. Although more commonly 10 - 20 cm between plants and 30 cm between rows are used. Seeds that have a diameter greater than 0.118 mm produce more vigorously growing seedlings that mature earlier. The best temperate climate for planting would be from spring to late summer, after the risk of frost has passed. For warmer climates, the planting times may be from mid to late spring and early autumn. As mentioned the plant does not tolerate frost autumn, so planting should preferably occur 6 weeks prior to the first frost.

Choi Sum is harvested between 30 to 50 days after sowing. The plants are harvested as the first flower buds begin to open by cutting with a sharp knife at the base. Seasonal yields with 2 to 3 harvests can usually be around 6 to 10 t/ha. You can expect a high quality product to have a white and tender stalk with developed but unopened yellow flower buds. The main stem should be long (at least 25cm) with a thick base (1.5 to 2.5 cm in diameter) and there should be no roots. The common post-harvest defects include open or deteriorating flowers and yellowed or decayed leaves.

Tsoi sum and cai xin (Chinese), cai ngot (Vietnamese), pakauyai or pakaukeo (Thai), saishin (Japanese), Chinese soup green, white flowering cabbage, mosk pak choy (English), Yau Choy, Yu Cai (Yeou Tsai), Chinese flowering cabbage oil greens, Yu Toy, and False Pak Choi.

Whole young leaves and stems, parts of larger leaves, and flowering shoots can be used in making salads. Choi Sum can be lightly boil, steam, stir-fry, combined with other greens and used in soups.

Cut off any woody portions of the stems and then slice the remaining stems and leaves into bite size pieces. Avoid steaming unless you prefer a very bitter taste. Lemon juice, garlic and red pepper flakes are great additions.

When storing Choi Sum cut off the thick stems below the twist tie. Then remove the twist tie from the stems to extend storage life. The tight ties can cause the stems to break down. Line a plastic bag with a paper towel to absorb excess moisture. Although best eaten when fresh, Choi Sum can be stored in the refrigerator for 5-7 days.

Try our Choi Sum recipes: Chilli beef and Choi Sum, Sichuan beef with Choi Sum, Choi Sum and lamb with vegetable chunks, Hokkien noodles with fired tofu, choi sum and prawns and Stir-fried cauliflower, choi sum, and beans (pad pak ruam)

UK: March-December     SPAIN: December-March

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