Wasabi

Wasabi, also known as Japanese horseradish, is a plant from the Brassicaceae family—the same group that includes horseradish and mustard. Its scientific name is *Eutrema japonicum* (formerly *Wasabia japonica*). Native to Japan, the Russian Far East (including Sakhalin), and the Korean Peninsula, it grows wild along stream beds in Japan’s mountain river valleys. The plant is cultivated for its rhizomes, which are grated into a pungent paste used as a condiment for sushi and other dishes.

The earliest known record of wasabi as food dates to the 8th century. Its popularity in English-speaking countries rose alongside sushi, steadily increasing from around 1980. Because the Japanese wasabi plant is difficult to mass-produce—it is sensitive to sunlight, requires temperatures between 8 and 20 °C, and needs high humidity in summer—it is expensive and scarce outside Japan. As a result, western horseradish is widely used as a substitute, often called "western wasabi" (西洋わさび) in Japan.

Taxonomically, the plant has a tangled history. Siebold named *Cochlearia wasabi* in 1830, noting its use as a condiment, but this was a *nomen nudum*. Maximovich’s 1873 name *Eutrema wasabi* is therefore illegitimate. The first valid description came from Miquel in 1866, who called it *Lunaria japonica* based on a Siebold specimen from Japan (exact location unknown). In 1899, Matsumura created the genus *Wasabia*, placing *Wasabia pungens* and *Wasabia hederaefolia* within it—both now considered synonyms of *Eutrema japonicum*. By 1912, Matsumura recognized *Wasabia japonica*, treating his earlier *Wasabia pungens* as a synonym. In 1930, Koidzumi moved the plant to the genus *Eutrema*, giving the accepted name *Eutrema japonicum* (Miq.) Koidz.

The plant has large, simple leaves that grow from long, thin stalks. Each leaf is 3 to 6 inches long and wide, with palmate veins. Wasabi flowers appear in clusters on long stems, blooming from late winter to early spring. In Japan, flowering begins in January due to cold-induced vernalization, peaks in April, and ends in May. Seed pods mature 50 to 60 days after flowering. Wasabi seeds have high dormancy and often fail to germinate; in nature, cold winter temperatures break this dormancy, with sprouting starting in February.

Culinarily, wasabi is primarily used to make a pungent paste. The part used is commonly called the "root," but it is more accurately the rhizome, stem, or the rhizome plus the base of the stem. Stores typically sell only this part. Fresh rhizomes are grated into paste and eaten in small amounts. Traditionally, coarse sharkskin was used for grating; modern kitchens use metal graters called *oroshigane*. Fresh wasabi paste loses flavor quickly if uncovered, so high-end restaurants grate it on the spot. Sushi chefs often place wasabi between the fish and rice to preserve its flavor. Store-bought paste is usually made from dried wasabi powder and sold in bottles or tubes.

Wasabi also flavors dry snacks. *Wasabi-mame* are legumes—peanuts, soybeans, or peas—roasted or fried and coated with wasabi powder. Fresh wasabi leaves can be eaten raw, though a common side effect is diarrhea. *Wasabizuke*, pickled wasabi leaves in sake lees, is a specialty of Shizuoka Prefecture.

Because true wasabi is hard to cultivate, a common substitute is a mixture of horseradish, mustard, starch, and green food coloring or spinach powder. Many products labeled "wasabi" contain no actual wasabi. The main difference is color: real wasabi is naturally green. Fresh horseradish has a similar but simpler flavor and texture—sharper, earthier, with a more noticeable pungent aftertaste. In Japan, horseradish is called *seiyō wasabi* ("western wasabi"). Outside Japan, a powdered mix of horseradish and mustard oil, known as *kona wasabi*, is used in most sushi restaurants, including reputable ones. In the United States, true wasabi is typically found only at specialty grocers and high-end restaurants.

The pungency of wasabi comes from allyl isothiocyanate, a volatile compound produced when allyl glucosinolate (a natural thioglucoside) is hydrolyzed by the enzyme myrosinase. This reaction occurs when the plant is grated, rupturing cells. The same compound gives horseradish and mustard their bite.