Japanese horseradish is a root vegetable that is widely used in Japanese cuisine. Known as “wasabi” in Japanese, the plant belongs to the botanical family Wasabia japonica. Japanese horseradish is available as a fresh root or as a commercially packaged paste or powder. It is most often used as a condiment for sushi.
The flavor of Japanese horseradish is peppery and more closely resembles hot mustard than chili peppers. It is also lachrymatory, which means that it induces tears. “Namida,” the Japanese word for “tears,” is used in association with wasabi on product labels or as a request for a sushi chef to use extra wasabi.
Wasabia japonica, the plant that produces Japanese horseradish, is generally difficult to cultivate. The edible root is a rhizome that thrives in flowing water. In its natural habitat, it grows near mountain streams, and for commercial production, it is grown hydroponically. Japanese horseradish is botanically related to cabbage and mustard, and its leaves are also edible.
Outside Japan, Wasabia japonica is cultivated in China, North America, and New Zealand. The most commonly cultivated varieties are daruma wasabi and matsuma wasabi. Matsuma wasabi is pale green and intensely peppery. The daruma variety is darker green and somewhat milder.
Fresh Japanese horseradish is available in some upscale grocery markets and health food stores. It is more commonly available in small tins in powdered form, or in tubes of wasabi paste. Many wasabi powders or pastes are made with ordinary horseradish root flavored with mustard and artificially colored, although some do contain a small percentage of real Japanese horseradish. A good indicator is the price, since genuine wasabi, whether fresh or packaged, is quite expensive.
To prepare fresh Japanese horseradish, the root is trimmed, peeled and finely grated. In Japan, utensils called “samezayano wasabi oroshi” are designed especially for this purpose. A fine metal grater may also be used. To prepare powdered wasabi, it must be mixed into a paste with a little water, which also brings out its peppery flavor.
In Japanese cuisine, a pinch of wasabi is usually served with sushi. It is believed to have anti-microbial effects that protect from the toxins in raw fish. The sushi chef rubs a dab of wasabi on sliced fish for nigiri sushi or on nori paper for makizushi rolls. It may also be mixed with soy sauce for dipping. In other foods, wasabi is used to flavor sauces, dressings, and crunchy snacks.