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Wasabi: Japan's spicy green gold

August 21, 2017

Wasabi – widely known as a nose-burning green condiment – is more than sushi’s sidekick. The first thing you should know is that it’s notoriously difficult to grow, making it eye-wateringly expensive. In fact, there’s a chance that the green paste on the side of your plate contains hardly any wasabi, but rather it might be a cunning mix of horseradish – especially if you’re eating it overseas.

Indigenous to Japan, the elusive wasabi plant first makes an appearance in historical records in the Asuka Period (527-710) when it was employed as medicinal herb. It was later eaten with raw fish as its antibacterial properties helped to remove the smell. Now, it’s a staple condiment with sushi and sashimi, soba (buckwheat noodles), and is even making appearances in Western food, replacing mustard as an accompaniment for beef.

Found naturally along shaded streams in Japan, its cultivation is believed to have begun 400 years ago in Shizuoka Prefecture, and has since expanded across Japan. It is even being grown overseas to meet increasing worldwide demand.

But to find out more about this tantalizingly spicy plant, I set off for Nagano Prefecture in central Japan, which produces the largest amount of wasabi in the country. My destination was in the rural area of Azumino, which draws the eyes with its ample waterways framed by picture-postcard mountains. This is the environment in which wasabi thrives.

In this region lies Daio Wasabi Farm, which stretches for 15 hectares. About 60,000 wasabi plants line waterways and ridges, laid out in a geometric, arrow-like pattern.
Squatting among them is Shigetoshi Hama, the impressively-titled Wasabi Master and PR Manager at the farm. At 72 years old, he joined the farm four years ago, moved by memories of a date with his first love at the very same location. His passion for the place shines through as he explains the secrets of Azumino and the green treasure it holds.

Wasabi needs a lot of running water but there’s plenty in supply – the area is fed by abundant reserves of spring water, which originates as melt water from the Northern Alps. An incredible 120,000 tons well up every day – according to Hama, that’s enough to provide water for a day in a town of 250,000 people!

This water, during its journey through the soil, picks up four key nutrients: potassium, nitrogen, lime and phosphorous. Nutrient-rich water is essential for wasabi grown hydroponically, which means without any soil. As Hama beautifully explains, "The fallen leaves of the forest are the father of wasabi, the spring water is its mother.”

Wasabi has earned its reputation as being difficult to grow for a reason. The water must be very clean and clear – any turbidity reduces oxygen levels, which stunts wasabi’s growth. What’s more, while it can survive temperatures in the negative in winter and nudging 30°C in the summer, it is exceptionally sensitive to water temperature. The optimum is between 10 and 15°C. The water at Azumino wells up at a cool 13 - 14°C but to avoid overheating, the plants are shaded by black cheesecloth nets between May and October. These may not be sightly, but they catch 80% of the sunlight.

These prized plants can only be harvested every one and a half to two years. Coupled with its particular growing requirements, it’s easy to understand why real wasabi will cost you a lot. Wasabi can fetch more than 5000 yen per kilogram at wholesale in Tokyo.

Fortunately wasabi is also a very versatile plant. Nearly every part can be eaten; only the roots are discarded. The upper stems and leaves can be employed in a variety of dishes, and are particularly good as tempura or pickles. But it is the rhizome, the main stem, which is most commonly sold in shops.

And it’s the rhizome that contains one of wasabi’s biggest secrets. If you take a slice or take a bite, it’s not spicy at all. Wasabi’s signature tingling sensation comes from the act of grating. This breaks down the plant’s cell structure, allowing an enzyme known as myrosinase to act on a natural chemical called sinigrin, producing a mustard oil. This might sound all very scientific, but the process is actually a clever natural defence against insects. Somehow it just hasn’t worked against us humans...

Traditionally, a sharkskin grater is used for wasabi preparation. Made of enamel, it breaks down the stem without producing excess heat, ensuring the creaminess of the paste. Yet wasabi rapidly loses flavor after grating. High-end restaurants recommend eating it within 15 minutes of grating, but Hama, channelling the true spirit of a Wasabi Master, advises eating it within just three!

I decided to do a little wasabi mastering of my own, and sample it as fresh as it comes. On the farm is a restaurant overlooking the rows of plants and running water. I ordered unadon – eel on rice – which came with a giant wasabi leaf and mini rhizome to grate by myself.

Grating the wasabi immediately released a clear, enticing fragrance. Fresh wasabi has a much cleaner taste – it begins with a slight bitterness, mellowing to sweet, and rushing up your nose if you’ve put too much in your mouth at once! But the flavor is refreshing and cuts through the richness of the eel (or equally of a fish like tuna), leaving a coolness after the spice. Eating fresh wasabi makes you feel as clear as the pure mountain water that went into growing it.

I found that wasabi leaves are surprisingly mild. I also tucked into one in a wasabi croquette burger, replete with wasabi mayonnaise – an extremely popular combination in Japan – and some wasabi juice, which was a kind of lemonade topped with wasabi to mix in.

Given the shade on the farm is mainly for the wasabi plants, it seemed somewhat compulsory after strolling around in the heat to enjoy a wasabi soft cream – milky with just a faint hint of wasabi tingling through.

However, if you don’t want to tuck into wasabi right away, pickling is a great option. I sampled some pickled upper stems mixed with sake kasu – leftover yeast after fermenting the rice to make sake. The spiciness of the stems cut through the richness and sweetness of the kasu, producing a flavor that teases your tongue and evolves as you eat it, leaving a signature cool finish.

New wasabi recipes and wasabi products are on the rise, from wasabi salad dressing to wasabi chocolate, reflecting a growing interest in both Japan and overseas. This trend is a testament to the complex and compelling flavor of this difficult-to-grow plant, once only found in shaded river valleys of Japan.

Text and photos: Phoebe Amoroso