Wasabi

Wasabi is the grated rhizome of Eutrema japonicum, formerly Wasabia japonica, a semi-aquatic brassica native to the cold, shaded headwater streams of the Japanese archipelago. It is one of the most demanding crops in world agriculture: the plant requires clean, running spring water held between twelve and fifteen degrees Celsius year-round, a gravel bed that drains instantly, and two to three years before a rhizome reaches marketable size — which is why genuine sawa-style wasabi reaches retail at roughly two hundred to five hundred euros a kilogram fresh. An estimated ninety-five percent of the «wasabi» served outside Japan, and much of that served inside it, is a substitute paste made from European horseradish, yellow mustard and green food dye. The authentic pungency comes from a unique family of six-methyl and seven-methyl-sulfinyl-alkyl isothiocyanates liberated the moment the rhizome is grated against a fine surface and the enzyme myrosinase meets the glucosinolate sinigrin. Those volatile compounds reach the nose through the retronasal pathway rather than burning the tongue like chilli capsaicin, and they degrade rapidly — a grated paste loses most of its heat within fifteen minutes, which is why sushi chefs grate it to order. The canonical grater is an oroshi made from a plank of wood covered in dried sharkskin, whose microscopic denticles tear rather than cut the tissue, maximising myrosinase release.