By the time most people encounter wasabi, as a dollop of pale green paste adorning their sushi platter, it bears little resemblance to its source. But though it may look more like Play-Doh than plant, real wasabi comes from the grated rootstock of the Wasabia japonica – a flowering plant native (as you may have guessed from its name) to Japan. Wasabi doesn’t just make your food hotter, it could also make it healthier. Studies have suggested that the plant may have certain antioxidant and antimicrobial properties. Good reason to eat more of it, right? Well, yes, except that if you live outside of Asia you may have never encountered real wasabi. It’s expensive stuff and thus a horseradish-derived substitute is frequently served in its place.*
Life before lunch
On the surface, the perennial wasabi plant is characterized by long-stemmed, clustered, heart-shaped leaves and white flowers. Underneath lies the rhizome, a root-like stem similar to that of the ginger that usually accompanies wasabi at sushi restaurants. While the leaves are also edible (and said to be deliciously spicy), it is the rhizome that furnishes mankind with one of its greatest condiments.
Wasabia japonica grows wild in the mountain river streambeds of Japan and, while it has been cultivated for well over a millennium, it isn’t the easiest plant to farm. It tends to be fussy about temperature (on the cool side, but not too cold) and lighting conditions (no direct sunlight, please). Semi-aquatic in nature, the species does best in constantly flowing water, but it can also be grown on land. Stream-grown “sawa” wasabi produces larger rhizomes and is considered to be higher quality than the field-grown “oka” wasabi.
Hot vs. Hot
If you’ve ever mistaken the wasabi on your plate for a piece of avocado that strayed from one of the rolls, you know that wasabi in large doses can be insanely hot. But unlike accidentally overdoing it with the Tabasco sauce, the experience probably didn’t leave you desperately gulping down water for the next half hour in a futile attempt to make the stinging stop. That’s because different chemicals are responsible for the spicy sensation of wasabi. Unlike the capsaicins that make hot peppers hot, which are oil-based and thus can linger uncomfortably on the tongue, wasabi gets its heat from volatile molecules called isothiocyanates that are felt more strongly in the nose. It’s a whirlwind hot that dissipates almost as soon as it starts. This is also why mild-mannered sake, or even tea, is a suitable beverage accompaniment for sushi, whereas chili pepper fueled curries do better with beer.
Under ideal circumstances, wasabi paste is made by simply grating the Wasabia japonica rhizome. The enzyme myrosinase, which reacts with other chemicals to make wasabi spicy, is locked in the cell wall of the plant so it is the grating (generally done with a very fine toothed “oroshi” grater) that actually releases the hotness. Wasabi needs to be served soon after the shredding is done, because the newly created heat fades quickly. However, the flavor can be preserved for longer by adding something acidic, such as vinegar, which coincidentally gives you the makings of a kick-ass vinaigrette.
Real wasabi is also sold as a powder that can be turned into a paste by simply mixing with water.† But you might want to read the ingredients before purchasing the powder for your DIY sushi garnish. Since wasabi rhizomes can be hard to come by, “wasabi powder” manufacturers have concocted a mixture of horseradish, mustard and food coloring to fool people like me. Although, assuming I”ve been eating pseudo-wasabi all along, I would add that it’s still pretty tasty.
Green on Green
Wasabia japonica has an impressive CV of potential medicinal uses. Studies have linked it to a variety of health benefits, including inhibition of tumor growth, reduction of cholesterol and the ability to ward off harmful bacteria. It may even help prevent tooth decay, not surprising once you recall that cavities are caused by bacteria. One of its more interesting benefits is a collaborative effort with a fellow member of the Brassicaceae family (more commonly called the cabbage family) – broccoli.
You may have heard broccoli being described as some kind of cancer-fighting super vegetable, a trick it achieves by way of the compound sulforaphane. Unfortunately, most people tend to cook much of broccoli’s medicinal properties right out of it. Luckily for those of you brutally over-boiling your greens, myrosinase (that same enzyme that gives wasabi its spicy kick) maximizes the effect of broccoli’s anti-cancer molecules.‡ For once, a flavor-enhancing ingredient also improves nutritional value.
* One North American cultivator sells the plant online for $100 (only $90 per pound if you buy two pounds)
† Interestingly, the powder also seems to be inert until the equivalent of grating – the addition of water – activates it. I learned this (completely anecdotal) information by attempting to make the above-mentioned wasabi vinaigrette over the weekend. Adding the powder directly to oil and vinegar yields a bitter and unspicy monstrosity of a dressing. But if you use water to make the powder into a paste first and then add the other ingredients all will be fabulous.
‡ A number of other myrosinase-containing veggies will also do the trick, including broccoli sprouts, mustard and horseradish (recall that those last two items make up the bulk of the cheaper pseudo-wasabi).
More Lifeforms from Alex Reshanov:
As a child, Alex Reshanov was told by grown-ups that she should consider becoming a lawyer (tendency to argue) or a comedian (frequent joking), so naturally she opted for science writing. In 2010, she started a personal blog, Blogus scientificus, as an outlet for her diverse scientific interests, random pop culture trivia and various phobias. Many of her posts have been published at EarthSky.