When most people think of wasabi, they think of the fiery-hot, greenish paste served with their sushi or sashimi. But they're probably eating extra hot Western horseradish, mixed with some soy sauce, hot Chinese mustard and a little green food coloring. Real wasabi is notoriously difficult to find, and expensive when it is found.

Wasabi is sometimes called Japanese horseradish, and its taste is very similar. Real wasabi — wasabia japonica — is a relative of the watercress family and an elusive little root. Like horseradish, it is a root, or rhizome, and it is grated or sliced for use in cooking. Wasabi is difficult to find because it is difficult to grow. It is expensive to buy because it is expensive to grow.

Wasabi is a fussy little plant, and has to be nurtured and brought carefully along like a delicate child. It takes about 18 months to reach its mature height of about 14 inches (36 cm). Wasabi requires a constant stream of cool water, but not too cool; shade, but not too much shade; and a mild climate. Thus, the United States is not ideal wasabi-growing country, except in the Pacific-Northwest, where growers have had some success with the plant. It is also grown successfully in New Zealand, as well as in Japan.

Sticker shock may seize anyone who buys a genuine wasabi root. A single root may cost $8-$10 US Dollars (USD), and wasabi roots run about $70-$100 USD per pound, depending on where the root was grown. Some Asian markets in larger cities may have fresh, genuine wasabi roots for sale, and a shopper will know he has the genuine article by the price tag.

When the wasabi is finally secured, it is prepared for eating raw by washing it, trimming any bumpy or scaly parts off with a sharp knife, and then grating it in a circular motion. A fine metal grater, such as a lemon zester, may be used, but real wasabi gourmands insist on a sharkskin grater, which they say produces a velvety grind. The grated wasabi is gathered into a ball and left to sit for a couple of minutes, to allow the heat and flavor to develop, then it is eaten. The traditional use is to eat it with sushi or sashimi, but it also may be used to flavor mustard or mayonnaise, as a meat sauce, or in salad dressings.

For those who simply cannot afford the genuine root, most cooks say the wasabi powder available in supermarkets will work nearly as well as the wasabia japonica.