The real stuff will cost you. (Ryan Sutton/Bloomberg News)

Think you like wasabi? Think again.

The little green balls that sting nostrils and line sushi platters around the world are very rarely what their name suggests.

What sushi restaurants actually serve alongside spicy tuna rolls is a horseradish-based concoction that is injected with green food coloring, infused with various types of mustard, and, often even, a bunch of other chemicals. Trevor Corson, the author of The Story of Sushi: An Unlikely Saga of Raw Fish and Rice, put it pretty starkly a few years back:

...it’s just plain old horseradish, plus some mix of mustard extract, citric acid, yellow dye no. 5, and blue dye no. 1. It comes in big industrial bags as a powder, and the chefs mix it with water before dinner to make that caustic paste.

What the Wasabi plant looks like. (Don Ryan/AP Photo) What the Wasabi plant looks like. (Don Ryan/AP Photo)

The real thing is quite different. True wasabi comes from the stem of the wasabi plant, which grows to nearly two feet long, and is famously finicky to harvest. It's most often sold by the stem, and served freshly grated. "It has a more delicate, complex, and sweeter flavor than the fake stuff you’re used to," according to Corson.

Very few people have tried the real thing, because the real thing is that rare. "The extent to which we're eating fake wasabi is huge," said Brian Oats, the president of Pacific Coast Wasabi, which bills itself as "North America’s only commercial grower of high-quality water-grown authentic Wasabi.". "Probably about 99 percent of wasabi is fake in the North America." That holds just about everywhere else, too. Even, though some might not realize it, in Japan. "I'd say about 95 percent is fake in Japan," he added.

Hiroko Shimbo, a sushi chef and the author of The Sushi Experience, agrees. "99 percent sounds about right," She said. "But it could be 95 percent."

And even in instances that real wasabi is used, it makes up a (very) negligible part of the paste—less than 1 percent, according to Oats.

The reason real, fresh wasabi is rarely served is mainly an issue of economics. There's a lot more demand than there is supply—largely because wasabi root is hard to grow and handle—and there has been for a long time. As a result, serving fresh, shaved wasabi to sushi goers, or even selling it dried in packages, would mean charging more than most customers were willing to pay—between $3 and $5 dollars for the typical ball served alongside sushi, according to Oats.

Rather than pair pricey raw fish with a popular but pricey flavor counterpart, the industry developed a considerably cheaper alternative—and long before sushi was popularized in the United States. "It was first created in Japan, before it came to America," said Shimbo. "People who love food, like 'foodies' from New York City, probably know this, but a lot of people don't."