Choy Sum

Name - While 'choy sum' is probably the most commonly used term in English, it's also potentially confusing.  The characters 菜心 (choy sum/cài xīn) translate to vegetable (or cabbage) heart - meaning the tender young heart of the plant.  The character 油 (yu/yóu) means 'oil,' and when added to the beginning of the term signifies this plant in particular.  That being said, if a vegetable is labeled choy sum, it's generally (but not always) yu choy sum, rather than another related cabbage species.

If you find a vegetable labeled yu choy (油菜) take note of the size.  If the plants are small and tender, it's yu choy sum, but larger, tougher plants are also sold.  These plants are cooked longer and tend to have a more pronounced mustard-like taste, so you want to be aware of the difference.

Preparation - Yu choy sum is extremely easy to prepare. Simply wash the leaves and stems gently in cold water. Make sure to wash around the base of the stems carefully, getting in between the stalks where dirt can build up. You may wish to trim the ends of the stems off if they’ve become a little dry.

Yu choy sum, while similar to gai lan in many respects, tends to be more tender. As such, the stalks are often cooked without trimming or cutting into smaller pieces. If desired, choy sum stalks and leaves can be separated for individual cooking. If you're cooking with older yu choy, the larger, firmer stems may require separation from the leaves and trimming to size or longer cooking.

Cooking - Yu choy and yu choy sum can apparently be eaten raw, however this seems to be a particularly unpopular choice with the exception of a few rare, sweet, thick-stemmed cultivars (which may or may not be of Mongolian origin). If you know of any traditional dishes that use raw yu choy, please get in touch!

Yu choy (sum) can be cooked in a variety of ways. As with many other Chinese vegetables, quicker cooking methods tend to be preferred. Yu choy sum stems tend to be tender enough that they can be cooked along with the leaves. With older yu choy, you may want to cook the stems separately (e.g. by adding them to a stir fry first) in order to avoid over-cooking the leaves. For both yu choy and yu choy sum methods like blanching or stir-frying will often yield the best results. Braising can yield good results as well, but make sure not to overcook the stalks, as this will reduce them to mush.

No other cruciferous vegetable has quite the same combination of flavour and texture, but there are some good alternatives.

First and foremost, it should be pointed out that yu choy and yu choy sum are already somewhat different, but can substitute for one another. Second, it’s worth noting that you may encounter other green plants grown or sold under the name ‘edible rape’ or ‘oil vegetable.’ These are very close relatives (or even the same plant), and can stand in readily. That being said, they are not generally available on a large commercial scale, though you may find them at some farmers’ markets and Chinese markets.

Gai lan makes a respectable replacement, thought it has a thicker stem (which requires longer cooking or cutting into smaller pieces) and a more broccoli-like flavour. Bok choy makes a good replacement from a flavour perspective, though it usually lacks some of the mustardy flavour of yu choy sum and a has different texture when cooked.

Outside of the Asian vegetables, rapini (broccoli raab/rabe) makes a good stand in. Like gai lan, it tends to be a bit tougher and more flavourful, and its bitterness is more pronounced. Interestingly, rapini is actually quite closely related to yu choy - both are edible members of the 'rape' group (Brassica rapa).

As already mentioned above, there is some inherent variation in the size and taste of this vegetable. When marketed as choy sum, it tends to be relatively small, tender, and mild. When it’s marketed as yu choy (or yau choy), it tends to be a little larger, tougher, and a little more strongly flavoured. For the record, they’re the same plant, just picked at different ages. There can be some overlap of course, given that growth is continuous.

There doesn’t tend to be much variety in commercially available yu choy (sum), but there are some interesting varieties available to home gardeners and in the occasional farmers market. There are some reddish/purple-stemmed varieties available, as well as some leafier varieties with more prominent flowers.