Have you ever eaten wasabi?

If you answered “yes” to that question, you are likely mistaken. Most sushi eaters—even in Japan—are actually being served a mixture of ground horseradish and green food coloring, splashed with a hint of Chinese mustard. Worldwide, experts believe that this imposter combination masquerades as wasabi about 99 percent of the time.

The reason boils down to supply and demand. Authentic wasabi, known as Wasabia japonica, is the most expensive crop in the world to grow. The temperamental semiaquatic herb, native to the mountain streams of central Japan, is notoriously difficult to cultivate. Once planted, it takes several years to harvest; even then, it doesn’t germinate unless conditions are perfect. Grated wasabi root loses its flavor within 15 minutes.

The Japanese have grown wasabi for more than four centuries. The 75-year-old Shigeo Iida, the eighth-generation owner of his family’s wasabi farm in Japan, takes pride in his tradition, which is profiled in Edwin Lee’s short documentary Wasabia Japonica, co-produced by Japan Curator. “Real wasabi, like the ones we grow, has a unique, fragrant taste that first hits the nose,” Iida says in the film. “The sweetness comes next, followed finally by spiciness.”

The film details Iida’s method of sustainable farming, known in Japan as tatamiishi. “It’s one of the most intricate organic farming systems,” Lee told me. Tatamiishi farms like Iida’s are built on sloped hillsides near rivers, harnessing the power of nature. Despite the plant’s finicky nature, Iida doesn’t use chemicals or fertilizers.

“In this day and age, where mass farming and manufacturing are dominant, it's refreshing to see a farming method that eschews modern technology,” Lee told me. “Tatamiishi farming results in some of the best wasabi in the world.”

Lee believes that many people would be surprised if they were afforded the chance to try real wasabi. “Like me,” he said, “it'll be difficult to go back to the fake stuff.”