Is the wasabi served with sushi real wasabi?

That little green blob on your sushi plate is one of the great impostors of the food world. If you have ever had a nose-tingling blast that made your eyes water, there is a good chance you have never actually tasted wasabi at all.

The short answer

Most of the time, the wasabi you are served is not real wasabi. It is usually horseradish, mixed with mustard and green food colouring. Real wasabi comes from the root-like stem, or rhizome, of a different plant, Wasabia japonica, and it is expensive and fussy enough that most restaurants do not use it.

The real story

Wasabi and horseradish are cousins. Both belong to the Brassicaceae family, which also includes mustard and radish. That is why they share a pungent kick. But they are different plants, and they taste different. Horseradish is sharp and harsh. Real wasabi is described as more fragrant, milder and slightly sweet, with a heat that complements raw fish rather than flattening it.

The problem is growing it. Wasabi likes cool, shady spots beside clear running water. In Japan it is traditionally grown in gravelly beds along mountain streams, such as in Nagano, and the plant takes around two years to mature. It dislikes direct sunlight and warm temperatures. Horseradish, by contrast, will grow almost anywhere. The result is a dramatic price gap: real wasabi rhizomes can sell for more than 70 US dollars a pound, while horseradish is cheap.

Real wasabi also has a short shelf life once prepared. Traditionally it is grated to order on a fine grater, sometimes one covered in sharkskin, producing a soft paste. Its aromatic compounds break down quickly, and the flavour fades within about 15 minutes. That makes it hard to dollop out in advance the way restaurants do with paste from a tube.

How common is the fake stuff? One food publication estimates that more than 99 percent of the wasabi sold in the United States is the horseradish mix, and that around 95 percent of wasabi products even in Japan are imitations. Exact figures are hard to pin down, but every source agrees that the real thing is the exception.

Why people get it wrong

It is green, it is called wasabi, it comes with sushi, and it burns your nose. Why would anyone suspect a swap? Most diners have never seen a fresh wasabi rhizome, so they have nothing to compare it to.

The labels do not help. Imitation wasabi is commonly sold simply as wasabi, and real wasabi is even sometimes misleadingly called Japanese horseradish. Unless your chef grates a knobbly green stem in front of you, assume you are eating the stunt double.

“If it came out of a tube and made you cry, mate, that was horseradish in a green costume.”