What is Wasabi? Your essential guide to Japan's rarest condiment

 

We are passionate about herbs, and Wasabi certainly ranks among the world's most extraordinary. Did you know approximately 90-95% of restaurants outside Japan aren't actually serving genuine Wasabi? That green paste with your sushi is typically horseradish, artificial colouring and mustard powder.

True Wasabi comes from the Wasabia japonica plant, a fascinating member of the Brassicaceae family alongside radishes and horseradish. This rare Japanese herb stands as one of the world's most expensive crops, fetching between £160-£250 per kilogramme.

We take immense pride in sharing our knowledge of speciality herbs, and Wasabi is particularly unique in its growing requirements:

• Needs to be partially submerged in water
• Thrives in specific temperature conditions
• Requires precise shade levels

This explains why the Izu Peninsula region in Shizuoka Prefecture produces approximately 70% of Japan's Wasabi. Throughout our guide, we'll share everything about this fascinating plant, from its authentic taste to whether you can grow it in your UK garden.

What is Wasabi, and where does it come from?

Wasabi's fascinating history stretches back centuries in Japan, with the earliest documented use dating to the Asuka period (538-710 CE). The term 'wasabi' first appeared in Japan's oldest medicinal plant encyclopaedia, 'Honzo Wamyo', highlighting its initial importance as a health remedy rather than just a condiment.

The Wasabi plant: Wasabia japonica

Botanically known as Wasabia japonica or Eutrema japonicum, Wasabi belongs to the Brassicaceae family alongside horseradish, mustard, and cabbage. This perennial plant is native to Japan, the Russian Far East including Sakhalin, and the Korean Peninsula.

Wasabi grows naturally along mountain stream beds where it thrives in clear running water. The plant features large, heart-shaped leaves and produces clusters of fragrant white flowers in early spring. While many refer to Wasabi as a root, it's technically a rhizome – a modified, underground stem that sends out roots and shoots from its nodes.

How Wasabi is traditionally used in Japan

Throughout Japanese culinary history, Wasabi evolved from a medicinal herb to an essential condiment. Its popularity as a seasoning for sushi began during the Bunka/Bunsei era (1804-1830) of the Edo period. Japanese chefs traditionally prepare Wasabi by grating the fresh rhizome against a coarse sharkskin grater called an oroshigane.

Wasabi's antimicrobial properties made it particularly valuable in pre-refrigeration Japan, where it helped reduce fishy odours, inhibit bacterial growth, and prevent food poisoning. Beyond sushi and sashimi, Wasabi appears in numerous Japanese dishes, including noodles like udon.

What is Wasabi made of?

The distinctive pungency in Wasabi comes primarily from allyl isothiocyanate, though its chemical composition differs significantly from horseradish. When wasabi cells are broken through grating, this compound is released through hydrolysis of naturally occurring glucosinolates.

Different parts of the wasabi plant offer varying culinary uses:

• The rhizome provides the familiar spicy paste
• The leaves can be eaten raw or cooked, carrying a milder spiciness
• The leaf stems (petioles) are often pickled
• The delicate white flowers serve as edible garnishes

Several varieties exist, including:

• Hon wasabi (本わさび): 100% pure wasabi rhizome
• Nama wasabi: Freshly grated hon wasabi without additives
• Yama wasabi: A white variant from Hokkaido known for extra spiciness

Wasabi contains several beneficial compounds besides its pungent isothiocyanates. Researchers have identified compounds like "Wasabi-sulfinyl™" and "Wasabi-flavone™" extracted from various parts of the plant, each with unique properties.

Real vs fake Wasabi: How to spot the difference

That green paste on your sushi plate? We hate to break it to you, but it's almost certainly not genuine Wasabi. Most diners outside Japan have never tasted genuine Wasabi, as approximately 95% of "wasabi" served globally is actually an imitation product.

What's in Wasabi paste sold outside Japan?

Numerous commercial wasabi products have been analysed and found they typically contain:

• Horseradish (70-95% of the mixture)
• Mustard powder
• Cornstarch
• Artificial food colouring (often E133 Brilliant Blue and E102 Tartrazine)
• Various stabilisers

This combination creates a reasonable approximation of Wasabi's pungency but lacks the complex flavour profile of the genuine article.

 

How to tell if your Wasabi is real

Genuine Wasabi has several distinguishing characteristics:

Appearance: Real Wasabi is a pale, natural green colour with visible plant fibre texture, not the uniform bright green of imitations.

Preparation: Authentic Wasabi is freshly grated at your table or just before serving, not squeezed from a tube.

Taste: The flavour of real Wasabi is complex with a sweet, vegetal undertone followed by heat that dissipates within 10-30 seconds. In contrast, imitation wasabi delivers a more aggressive, longer-lasting heat with a simpler flavour profile.

Price: If you're paying only a small amount for Wasabi or receiving it freely with inexpensive sushi, it's almost certainly fake.

Grow Genuine Wasabi at home - supplied by Culinary Herb Co.

At Culinary Herb Co., we’re on a mission to make herbs accessible to passionate UK growers - and our Wasabi (Eutrema japonicum) plants are a perfect example. This isn’t some horseradish knock-off, it’s the real deal: the same elusive, shade-loving rhizome revered by Japanese chefs and sought after by herb collectors worldwide.

We supply established wasabi plants grown right here in the UK, ready to settle into your shady garden spot or a large container with consistent moisture. Our Wasabi is not at seedling stage - you’re getting a well-rooted plant that’s been carefully nurtured to thrive in British conditions. With patience, care, and the right growing environment, you’ll be able to harvest the prized rhizome in 18–24 months. In the meantime, you can enjoy the edible leaves and stems, which offer a more delicate version of that distinctive wasabi heat.

Growing conditions Wasabi plants demand

We've studied the specific growing conditions that these temperamental plants require:

• Temperatures consistently between 8-20°C
• Shade from direct sunlight (at least 75% shade)
• High humidity, especially in summer
• Constant access to clean water
• Well-draining yet continuously moist soil.

These stringent requirements mimic Wasabi's natural habitat - misty mountain stream beds in Japan, where the plants grow partially submerged in flowing water. From our experience with delicate herbs, even minor environmental changes can stress or kill wasabi plants, making commercial cultivation exceptionally difficult.

Regions in Japan famous for Wasabi farming

Japan remains the heart of wasabi production, with specific regions dominating cultivation:

• Shizuoka Prefecture (particularly the Izu Peninsula) produces approximately 70% of Japan's Wasabi
• Nagano Prefecture, home to the Daio Wasabi Farm - the world's largest commercial wasabi operation
• Iwate Prefecture, leading in hata-wasabi (field-grown wasabi) production
• Shimane Prefecture, known for its Hikimi wasabi

We've found these areas possess the ideal combination of clean mountain water, suitable climate, and traditional farming expertise developed over centuries.

Can you grow Wasabi at home or in the UK?

Growing Wasabi at home or in the UK presents challenges yet remains possible. The UK has at least one commercial wasabi operation in Dorset/Hampshire. We're particularly excited that some of our customers have successfully grown this treasure in their gardens.

For home cultivation, Wasabi can survive British winters (tolerating temperatures down to -5°C with protection) and thrives in shaded areas like north-facing garden spots. Container growing works with a minimum 9-litre pot size, provided you maintain consistent moisture without waterlogging. Throughout this long growing period of 18-24 months, you can harvest the edible leaves, stems and flowers while waiting for the prized rhizome to develop.

What does Wasabi taste like, and is it good for you?

Wasabi creates a sensory journey unlike any other herb - beginning in your mouth and travelling upward rather than lingering like chilli heat.

The true Wasabi taste experience

Real Wasabi delivers a complex flavour profile that we absolutely adore. It starts with a fresh, herbaceous taste followed by a sharp heat that quickly disappears, leaving a surprisingly sweet aftertaste. This clean, powerful, yet fleeting spiciness makes Wasabi uniquely refreshing among herbs.

Fake Wasabi (horseradish-based) produces a harsher, more pungent sensation that lingers uncomfortably, lacking the nuanced, aromatic notes and gentle sweetness found only in the genuine article.

Why Wasabi's heat travels to your nose

Unlike chilli peppers that primarily affect your tongue through capsaicin, Wasabi's heat targets your nasal passages. This occurs because Wasabi contains allyl isothiocyanate, a highly volatile compound that immediately vaporises in your mouth.

When eaten, these vapours travel through the back of your mouth into your nasal cavity, where they activate the TRPA1 ion channel in sensory neuron endings. This creates that familiar nose-tingling sensation without the prolonged burn of oil-based spices.

Our final thoughts on Wasabi

We consider Wasabi one of the world's most extraordinary culinary herbs. Though genuine Wasabi remains exceptionally rare outside Japan, understanding its authentic character helps explain why this plant commands such respect and premium prices. Unlike its common horseradish-based impostor, real Wasabi delivers a complex, fleeting heat with a subtle sweetness that truly transforms the dining experience.

The extreme growing conditions required by this temperamental plant explain both its scarcity and expense. Despite these challenges, dedicated growers have successfully cultivated Wasabi beyond Japan, including here in the UK, where our shaded, moist conditions can provide suitable environments for ambitious gardeners.

Whether you seek out a high-end Japanese restaurant serving freshly grated Wasabi or attempt to grow your own wasabi plants, experiencing the genuine article proves worthwhile. This green treasure, traditionally grated moments before serving on sharkskin graters, offers a true taste of Japanese culinary heritage that few Western diners ever encounter.

The next time you see that familiar green paste alongside your sushi, you'll certainly know whether you're experiencing Japan's rarest herb condiment or simply its widespread imitation.

Frequently Asked Questions about Wasabi.

What is real Wasabi, and how does it differ from imitation?

Real Wasabi comes from the Wasabia japonica plant and has a complex, fresh flavour with a quick heat that dissipates rapidly. Most Wasabi served outside Japan is actually a mixture of horseradish, mustard, and food colouring, which has a harsher, longer-lasting heat.

Why is authentic Wasabi so expensive?

Genuine Wasabi is costly due to its specific growing requirements, including cool temperatures, clean flowing water, and shade. It takes up to three years to cultivate and is susceptible to pests and diseases, resulting in limited supply and high prices.

How do Japanese people typically use Wasabi?

In Japan, Wasabi is primarily used with sushi and sashimi, where chefs often add a small amount directly to the dish. It's also used in cold noodle dipping sauces, as a topping for rice, and in various side dishes and marinades.

Can Wasabi be grown at home?

While challenging, it is possible to grow Wasabi at home, as we at Culinary Herb Co. do. It requires specific conditions like shade, consistent moisture, and temperatures between 8-20°C. Container growing is possible with a minimum 9-litre pot size, but it takes 18-24 months for the rhizome to mature.

Is Wasabi Powder the same as fresh Wasabi?

Not quite. Wasabi powder is typically made from dried horseradish and mustard, with a dash of green food colouring to mimic the appearance of real Wasabi. While some high-quality powders contain trace amounts of Wasabia japonica, most fall short of replicating the nuanced flavour and quick-vanishing heat of freshly grated Wasabi rhizome. If you’re after an authentic experience, fresh is best.

What is Western Wasabi and how does it compare?

“Western Wasabi” is often a polite way of describing the horseradish-based imitation served in most non-Japanese restaurants. While it packs a similar spicy punch, the flavour of real Wasabi is notably more complex - herbaceous, sweet, and fleeting. Western Wasabi lacks the clean nasal heat and fragrant profile of the true Japanese wasabi plant, Wasabia japonica.

Why is Wasabi often mixed with green food colouring?

Because real Wasabi is rare and expensive, most commercial pastes use green food colouring (often E102 or E133) to resemble the natural pale-green hue of fresh Wasabi. This visual mimicry helps maintain the illusion, but don’t be fooled - if the colour is unnaturally bright or fluorescent, it’s likely not the real deal.

Does Wasabi contain soybean oil or other additives?

Real Wasabi should never contain soybean oil. However, many imitation Wasabi products - especially those sold in tubes or powders - use soybean oil, emulsifiers, and stabilisers to create a paste-like consistency and prolong shelf life. Always check the ingredients list if you’re unsure.

Is Wasabi used in a wide range of dishes beyond sushi?

Absolutely. While most famous as a sushi companion, Wasabi features in a wide range of Japanese cuisine. It’s used in noodle broths, salad dressings, marinades, pickled side dishes, and even desserts like ice cream and chocolate. Its versatile flavour lends itself to both savoury and sweet creations when used thoughtfully.

What gives Wasabi its unique flavour and spicy kick?

The flavour of Wasabi comes from a volatile compound called allyl isothiocyanate, produced when the plant’s cells are broken. Unlike chilli heat that lingers on the tongue, wasabi spicy heat rises quickly into the nasal passages and fades within seconds. This ephemeral heat is one of the herb’s most celebrated traits.

What’s the difference between Wasabi and the Japanese wasabi plant?

‘Wasabi’ commonly refers to the prepared condiment, but it originates from the Japanese wasabi plant Wasabia japonica (also known as Eutrema japonicum). This shade-loving perennial produces the rhizome we grate into Wasabi paste. It also offers edible leaves, stems, and flowers - each with a milder expression of the plant’s signature heat.

Is Wasabi spicy in the same way as chillies?

Not at all. Wasabi’s spice is aromatic, not oily. It activates receptors in the nasal passages rather than the tongue, creating a short-lived but intense hit that quickly fades. The sensation is often described as “clean heat” - refreshing and intense but never lingering or numbing like chilli.

What chemical in Wasabi causes the nose-tingling sensation?

The culprit is allyl isothiocyanate - a natural compound also found in mustard and horseradish. In Wasabi, it’s released when the rhizome is grated. Because it’s highly volatile, it vaporises quickly, stimulating nerve endings in your nasal cavity and producing that distinctive head-clearing tingle.