Wasabi is the bright, pale-green spicy condiment traditionally served alongside sushi. Made from Japanese horseradish, wasabi is usually served as a paste to flavor foods. Like horseradish, wasabi has a spicy, pungent flavor. Make wasabi paste from powdered wasabi mixed with water, or by grating fresh wasabi root.
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Fresh wasabi paste comes only from the fresh root. Powdered wasabi is sometimes made from dried, powdered Japanese wasabi root. More often though, wasabi powder is only dyed-green, powdered horseradish.
Fresh wasabi root takes a long time to mature -- around 2 years -- and is highly perishable. Because of that, it is rarely available to home cooks outside of Japan. The root is knobby with a distinctive green color. Store fresh wasabi root in the refrigerator, wrapped in a damp paper towel. Peel off any darkened portions before using. Stored in the fridge and kept damp, the root will keep for 3 weeks.
Powdered wasabi made from wasabi root contains only Wasabia japonica. But, most wasabi powder or pre-made wasabi paste does not contain wasabi root because of the expense.
Making Wasabi Paste
Steps for making wasabi paste depend on whether you use fresh wasabi root or wasabi powder.
To make wasabi paste from fresh wasabi:
Peel the skin of the root with a vegetable peeler. Remove any knots or rootlets.
Grate the peeled root using a fine mesh grater or a dedicated wasabi grater. A wasabi grater, made from sharkskin or ceramic, has a rough surface as opposed to a series of holes, as are found on a standard grater.
Grate the root in a circular motion until there is enough paste. Serve the paste within 10 to 15 minutes of grating, as the flavor compounds quickly disperse from fresh wasabi root.
Combine powdered wasabi with cold water that is free of chemicals, such as chlorine or salts. Use, roughly, a 3-2 ratio of powder to water. A 1 1/2-teaspoon serving of wasabi powder needs approximately 1 teaspoon of cold water. The more water used, the thinner the texture of the paste. Let the paste rest 5 to 10 minutes before serving, either in the fridge or at room temperature.
In addition to serving alongside sushi and sashimi, use wasabi paste to season a range of foods. Serve the paste with steak or oysters in place of horseradish. A common use of the paste is to season potatoes, such as mashed potatoes. Wasabi paste is sometimes mixed with mayonnaise to make an aioli for fish or french fries. Substitute chilies in a recipe with wasabi paste, such as for seviche or in a salad dressing, to give a dish an Asian flair.