Wasabi is a popular sushi condiment made from the root of the Wasabia japonica plant, which grows in Japan and a few moist, temperate areas of the United States. To make wasabi, it’s necessary to either obtain a fresh wasabi root for grating into a paste or buy wasabi powder made from the dried roots. Wasabi powder can be reconstituted with water alone or with other ingredients to make wasabi paste. Once prepared, fresh wasabi retains full flavor for only around 15 minutes. Grated fresh wasabi should be used immediately.
The wasabi plant is very difficult to cultivate, and the root is rare and expensive to purchase. As the flavor of fresh wasabi dissipates so quickly, advance preparation of fresh wasabi is nearly impossible. Wasabi should be prepared immediately before consumption to savor the full flavor.
Nearly all wasabi served with sushi is actually not wasabi. It is a blend of horseradish, mustard, and green food coloring that closely approximates the flavor and appearance of real wasabi. Most wasabi paste and sauce sold in supermarkets are also made from horseradish, with little or no actual wasabi.
A cook has three options for preparing wasabi. Fresh wasabi can be grated from a fresh wasabi root. Although difficult to obtain, fresh wasabi root can be secured online either from Japanese or American growers. To make wasabi in the traditional Japanese manner, a special tool made from dried shark skin can be used to grate wasabi into a paste. If this tool is not available, any fine grater can be used.
In the absence of fresh wasabi root, dried wasabi powder can be used to make wasabi paste. Dried wasabi has the advantage of storing more easily than the fresh root, which must be refrigerated and used within two weeks. The powder retains much, but not all, of the original flavor of fresh wasabi if it has been manufactured correctly. It can be stored indefinitely and mixed with water, oil, or soy sauce to make a paste and diluted according to personal taste. To store leftover wasabi paste, mix with a small amount of oil and store in the refrigerator.
Perhaps the simplest option for making wasabi, if not the most authentic, is to make it from a mixture of horseradish, mustard, and green food coloring, as many Japanese and sushi restaurants do. The flavor of this mixture is similar to fresh wasabi and keeps longer. Most people have not tasted real wasabi and so won’t be able to discern the difference.