Wasabi is a spicy paste that is commonly served with sushi and sashimi. It is made from the rhizome of the Wasabia japonica plant, which is part of the Brassicaceae family. The rhizome is the underground stem of the plant, which is grated to create the paste. Real wasabi is difficult to grow and is expensive, so most wasabi found in grocery stores and with prepackaged sushi is made of powdered horseradish and artificial color. It may also contain mustard powder and thickening agents like flour or cornstarch. The fake wasabi is much hotter and longer because it is made from horseradish and sometimes mustard. To spot fake wasabi, first look at the texture. A pasty and thick consistency is a sign of imitation wasabi, while real wasabi is more fibrous.