Most wasabi served outside Japan is horseradish with green food colouring.
Real wasabi is a root that is hard to grow and loses its flavour within minutes of being grated. The green paste in most sushi restaurants is a mix of horseradish, mustard and dye.
Why is this true?
Wasabi needs cool, clean running water and years to mature, so it is expensive even in Japan. Horseradish delivers a similar nose-burning kick from closely related compounds for a fraction of the price.
More facts in this category
More about food
Food facts sit right where biology, chemistry and history overlap. A fruit that is technically a berry, a spice worth more per gram than silver, a sweetener that never spoils in a sealed jar — the reasons usually come down to sugar, acid, water and how long humans have been moving plants around the planet. Each entry explains the mechanism in plain language, and links to a source if you want the longer version.