Wasabi

Wasabi, also called Japanese horseradish, is a member of the Brassicaceae family—the same group that includes horseradish and mustard. It grows naturally along mountain stream beds in Japan and is also native to the Russian Far East (including Sakhalin) and the Korean Peninsula. The plant is grown for its rhizomes, which are ground into a paste and used as a pungent condiment for sushi and other dishes. Unlike chili peppers, wasabi’s heat hits the nose more than the tongue, and freshly grated wasabi has a subtly distinct flavor.

The earliest known record of wasabi as a food dates to the 8th century. Its popularity in English-speaking countries grew steadily from around 1980, alongside the rise of sushi. Because the Japanese wasabi plant is difficult to cultivate on a large scale—it’s sensitive to sunlight, requires cool temperatures, and needs high humidity—it’s expensive and hard to find outside Japan. As a result, most “wasabi” sold abroad is actually a mixture of horseradish, mustard, starch, and green coloring. In Japan, this substitute is called “western wasabi.”

The plant’s taxonomy has a tangled history. Siebold named it *Cochlearia wasabi* in 1830, but that name was invalid. Maximovich’s *Eutrema wasabi* (1873) was also illegitimate. The first valid description came from Miquel in 1866, who called it *Lunaria japonica*. In 1899, Matsumura created the genus *Wasabia*, with two species now considered synonyms of *Eutrema japonicum*. By 1912, he recognized *Wasabia japonica*, and in 1930, Koidzumi moved the plant to the genus *Eutrema*, giving it the current scientific name.

The plant has large, simple leaves—3 to 6 inches long and wide—with palmate veins, growing from long, thin stalks. Wasabi flowers bloom in clusters on long stems from late winter to early spring. In Japan, flowering starts in January due to cold-induced vernalization, peaks in April, and ends in May. Seed pods mature 50 to 60 days after flowering. The seeds are highly dormant and often fail to germinate; in nature, winter cold breaks dormancy, and sprouting begins in February.

Culinarily, wasabi is mostly used as a paste made from the rhizome (sometimes called the root, though it’s actually the stem or rhizome plus stem base). Fresh rhizomes are grated—traditionally on sharkskin, now often on metal graters—and eaten in small amounts. The paste loses flavor quickly if uncovered, so high-end restaurants grate it on the spot, and sushi chefs often place it between the fish and rice to preserve its taste. Store-bought wasabi paste is typically made from dried powder and sold in bottles or tubes.

Wasabi also flavors snacks like *wasabi-mame*—roasted or fried legumes (peanuts, soybeans, or peas) coated in wasabi powder. Fresh leaves can be eaten raw but may cause diarrhea. *Wasabizuke*, pickled wasabi leaves in sake lees, is a specialty of Shizuoka Prefecture.

Because wasabi is hard to grow commercially, a common substitute is horseradish mixed with mustard, starch, and green food coloring or spinach powder. Many products labeled “wasabi” contain no actual wasabi. Fresh horseradish has a similar but simpler flavor—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, *kona wasabi*, is used in most sushi restaurants, including reputable ones. In the United States, true wasabi is usually found only at specialty grocers and high-end restaurants.

The pungency of wasabi comes from allyl isothiocyanate, a volatile compound produced when the enzyme myrosinase breaks down allyl glucosinolate during grating. The same compound gives horseradish and mustard their heat.