Wasabi

Wasabi grows in cold running water on gravel beds, takes a year or two to reach a usable size, and dislikes almost every condition a farmer can arrange. Shizuoka built terraced water fields for it centuries ago. Because the plant is slow and fussy, real wasabi is expensive, and most of what appears on a supermarket tray is European horseradish with mustard and green dye.

The heat behaves differently from chilli. Grating the rhizome breaks cells and releases a compound that turns to vapour, so the burn goes up into the nose rather than sitting on the tongue, and it fades within about fifteen minutes. That decay is why a good sushi counter grates it to order, traditionally on a paddle covered with sharkskin, which produces a finer paste than a metal grater.

At a proper counter the chef has already put the right amount between rice and fish, and stirring a lump of it into your soy sauce is the move that marks you as a tourist. The plant's leaves and stems are edible too, pickled or served as tempura, though almost nothing outside Japan sells them.