The Secrets of Wasabi

Wasabi is one of the world's most expensive crops. But even if you enjoy sushi, you might never have tasted the real thing.

Wasabi is one of the world’s most expensive crops, currently priced at $160 USD per kilogram. It’s not the most expensive food you could buy - a kilogram of saffron could be $15,000 USD, and a kilogram of Black Ivory elephant dung bean coffee costs $1,800 USD.¹ But it is one of the hardest crops to grow.

The most popular wasabi species is Wasabi japonica, which evolved to grow in the gravel beds of mountain streams in Japan. It doesn’t like direct sunlight, and it takes two years to grow to maturity. It was listed as a medicinal plant in a Japanese medical encyclopaedia in 918 AD and was cultivated from 1596 to 1615 AD. At first, only the ruling class were allowed to use it.² Yet, by the 19th century, common people were eating wasabi as a sushi seasoning, and by the 20th century, sushi had gained global popularity.

Why is wasabi spicy and bitter?

Wasabi is part of a group of plants known as the mustards or cabbage family. This group includes less obviously spicy vegetables like Brussels sprouts, cabbages, kale and cauliflower. But all of these plants contain a secret sting. Inside their cells, they hold stores of an enzyme called myrosinase and organic molecules called glucosinolates.

When damaged - like by a chomping predator - the myrosinase and glucosinolates mix together and start reacting. The result? A variety of molecules which evoke bitter and spicy flavours. Chief among these molecules are isothiocyanates.

Isothiocyanates trigger special sensors in our cells, which some scientists have dubbed the ‘wasabi receptor’, or less colourfully, TRPA1. These sensors are our body’s ‘fire alarm’, and they create feelings of pain and inflammation. TRPA1 sensors can also be activated by capsaicin from chilli peppers, acids, high temperatures, and pollutants. It’s the lining of TRPA1 sensors in your airway which makes you cough if you inhale smoke.³

Freshly grated wasabi will reach peak spiciness after about a minute, then lose its flavour after 15 minutes.

The cocktail of different types and amounts of isothiocyanates is why a bite of raw kale tastes bitter, and mustard is spicy. Wasabi contains over 3000 times more isothiocyanates than cabbage.⁴ But isothiocyanates are very volatile and evaporate quickly.

So what is wasabi made of, and what have I been eating?

Early in the 20th century, a tea broker in Japan had the idea of drying wasabi and selling it as a powder. But powdered wasabi lost most of its volatile pungency and flavour. To compensate for this, wasabi blended with horseradish and mustard powder started to be sold.⁵ More modern techniques like freezing wasabi at an ultra-low temperature (-196°C) using liquid nitrogen are more successful at preserving its flavour, as it stops the enzymic reaction.

In essence, that’s why most wasabi condiments outside of Japan contain mostly horseradish and mustard and very little wasabi at all. At restaurants, real wasabi should be served as the root (rhizome) with a piece of sharkskin or metal to grate it on.

More than a flavour

So, if Wasabi trips our TRPA1 sensors, is it bad for us? Not at all. It became popular to use on raw fish because it made people less likely to get sick.⁶ Remember isothiocyanates? Scientists have found these molecules have a number of useful properties, like killing harmful bacteria. Japanese company WasaOuro uses flavourless wasabi extract as a coating for food packaging.⁷ Scientists even proposed wasabi isothiocyanates could help prevent tooth decay. They can also lower the risk of blood clots, show anti-cancer properties, and assist against asthma.⁸

TRPA1 receptors are particularly concentrated in the nasal passages. An Ig Nobel prize was awarded to a fire alarm which released wasabi isothiocyanates when smoke was detected. Out of 100 tested odours, the irritating effects of the wasabi gas were best at waking up sleeping volunteers.⁹ Just don’t go too far. A woman suffered ‘broken heart syndrome’ after eating an unusually large amount of wasabi. She had mistaken it for avocado.¹⁰
 

Broken heart syndrome is a condition caused by stress or extreme emotions - causing temporary damage to a person's heart.

Where next?

Image credit: The Functional Plant Company

Wasabi isn’t meant to be spread liberally over sushi. Sushi masters, like Jiri Ono, usually apply the amount of wasabi, depending on the type of sushi they create.¹¹ The wasabi also helps to stick fish layers to the rice underneath. And beyond sushi, there’s wasabi peas, wasabi gin, wasabi ice cream... By 2013, Japan produced over 17 000 tons of wasabi. But global demand still outstrips supply.

Cultivation of wasabi has now spread to countries such as Taiwan, China, America, Canada, the UK, New Zealand and Tasmania. And new technologies, like those of the Functional Plant company in Scotland, are making wasabi easier to grow. “Cloned tissue doesn’t have any of the issues that sometimes are inherent after growing several generations of wasabi,” said Janet Colston, co-owner of The Functional Plant Company, which produces wasabi seedlings by cloning, growing in hydroponics (nutrient-filled water) and LED lighting.¹²

"I think it’s becoming more known in the west. People are less fearful of that two-year growing cycle. And what we hope to do is encourage more people to understand that it’s possible to grow wasabi using our new farming methods."

So perhaps we’ll be enjoying the taste – and health benefits – of real wasabi soon.