I'll take an unagi roll, some tuna nigiri and a side of lies, please. Image: J RAWLS
The dab of spicy green paste that accompanies your sushi may go by the name wasabi, but it's actually something else entirely. What we call wasabi is almost always just a mix of horseradish, mustard and a bit of green dye.
Because of similarities in their chemical compounds, which you can see detailed below in a new video from the American Chemical Society's Reactions series, horseradish makes a less-spicy (but passable) substitute for wasabi. Why aren't sushi restaurants just serving the real thing?
Wasabi has a reputation as one of the hardest crops to successfully farm. It doesn't like direct sunlight, but doesn't want complete shade either. It does well only in mild climates that aren't ever very hot or cold. And, even when you do manage to get wasabi to grow, it tends to do best in small plots, not large farms.
Given how hard it is to grow, and how often it fails, it's no big surprise that real wasabi is extremely expensive, costing about $US160 ($210) per kilogram. Restaurant guests aren't used to paying for the condiment at all, much less paying more for it than for the sushi itself. So instead of real wasabi, a much cheaper substitute is served — one that people won't be able to distinguish from the real thing because they have never had the real thing.
But how can you tell if your wasabi is real? If you're eating real wasabi, you almost certainly grated it yourself or had it grated in front of you. If it came out in a paste on the plate, then you probably had some lightly-dyed (but still tasty) horseradish.