Because no sushi experience would be complete without that dollop of wasabi adding its zing, it may come as a surprise that most sushi lovers have never eaten real wasabi.
The pistachio-green paste on your plate might be called wasabi, but it’s most likely just a mix of European horseradish, mustard, and food coloring. Even in Japan, the home of wasabi, the real thing is in short supply.
“Real” wasabi comes from the rootlike stem, or rhizome (think of fresh ginger), of Wasabia japonica. As a member of the Cruciferae family, it is related to such plants as cabbage, cauliflower, broccoli, and mustard. Its distant cousin European horseradish (Armoracia rusticana) often pinch-hits for it in culinary uses.
Wasabi grows naturally in mountain streambeds, and the Japanese have cultivated it for more than a millennium. Wasabi grown in semiaquatic conditions is known as sawa, whereas wasabi grown in fields is called oka. The stream-grown wasabi produces larger rhizomes and is generally considered to be of higher quality.
Unlike horseradish-based stand-ins, the heat of real wasabi dissipates quickly because of the volatility of the flavor components. “If you take imitation wasabi powder and add water, you can leave that almost overnight and it will still be hot,” says Brian Oates, president and chief scientific officer of Pacific Coast Wasabi, in Vancouver, British Columbia. “With wasabi, when you grate it up, it’s only good for, at most, 15 minutes.” The components of both wasabi and horseradish can be stabilized by acids, such as vinegar or lemon juice.
The key chemicals that give wasabi its characteristic heat and flavor aren’t present until the wasabi is macerated. When the cell wall is disrupted, it releases the enzyme myrosinase, which hydrolyzes glucosinolates, a group of sulfur-containing glucose derivatives, to produce isothiocyanates that provide wasabi’s spicy zing. The most abundant of these is allyl isothiocyanate.
“Horseradish has a different profile of isothiocyanates, and it is possible to taste the difference,” says Geoffrey P. Savage, an associate professor in the food group at Lincoln University, in Canterbury, New Zealand. “The problem is that not many people have tasted the original taste of wasabi, so they don’t know what they are tasting.”