Wasabi is a Japanese plant whose thick stem is grated to a green paste with a sweet, fresh, nose-tingling heat. Most wasabi served abroad is actually horseradish, mustard and green colouring.
What it is¶
True wasabi is a perennial in the cabbage family, native to Japan, where it grows wild along cold, shaded mountain streams. The part used is the thick, knobbly stem at the base of the plant — usually called a rhizome — which is grated to a fine, pale green paste just before eating.
Two ways of growing it are distinguished in Japan:
- Sawa wasabi (water wasabi), grown in beds of gravel with cold spring water running through them. It produces the prized stems.
- Oka wasabi (field wasabi), grown in soil. It gives smaller, less fine stems, and is often used for processed products.
Wasabi is notoriously slow and difficult to grow, taking roughly 18 months to two years or more to produce a usable stem, and it needs shade, cool temperatures and clean water. Fresh stems are expensive. As a result, the great majority of "wasabi" sold outside Japan — and a good deal inside it — is a paste or powder of horseradish, mustard and green colouring, sometimes with a little real wasabi added.
Origins and history¶
Wasabi appears in Japanese texts of the early 10th century, originally as a medicinal plant. Cultivation is generally traced to the early 17th century in the Utogi area of Shizuoka, near the Abe River, and the plant's rise in cooking went hand in hand with the growth of sushi and sashimi culture in Edo (now Tokyo). A popular story says the shogun Tokugawa Ieyasu so admired the plant that its cultivation was restricted; like many such stories, it is not well supported.
The powdered and tubed substitutes were developed in the 20th century, making the flavour cheap and widespread just as Japanese food became popular abroad. Real wasabi has since been grown commercially outside Japan, including farms in southern England since around 2010.
Flavour and aroma¶
Freshly grated real wasabi is less brutally hot than the tubed kind. Its heat is clean and sweet, with a green, herbal, slightly vegetal flavour, and it rushes up into the nose rather than burning the tongue. The pungency comes from isothiocyanates released when grating ruptures the plant's cells and lets the enzyme myrosinase act on glucosinolates — the same chemistry as mustard and horseradish. Real wasabi produces a broader mix of these compounds, which is thought to account for its fresher, more complex aroma.
The heat peaks a few minutes after grating and fades within about 15–20 minutes, which is why it is grated to order.
In the kitchen¶
- Grate the stem, top end first, in small circles on a very fine grater: traditionally a sharkskin grater (samegawa oroshi) or a fine metal oroshigane. Fine grating ruptures more cells and gives more heat and sweetness.
- Rest the grated paste for 2–3 minutes to develop, then use within 15 minutes.
- With sushi and sashimi: a small dab placed on the fish (or between fish and rice in nigiri). In Japan, stirring wasabi into soy sauce is common but traditionally frowned on for good sushi.
- With soba: stirred into the dipping sauce.
- With beef: fresh wasabi and salt with grilled steak is a Japanese pairing, and excellent.
- Leaves and stalks: edible, peppery and good in salads, tempura or pickled as wasabi-zuke with sake lees.
- Tubes and powders: mix powder with an equal volume of cold water and leave 5 minutes, covered, to develop.
💡 Keep it cold
Wrap an unused stem in damp kitchen paper, then cling film, and keep it in the coldest part of the fridge; rinse it and change the paper every few days. Cut off the grated end's browned surface before grating again. A fresh stem keeps for two to four weeks.
Buying and storing¶
Fresh stems: as above. Frozen grated wasabi keeps for months and is a good compromise. Opened tubes belong in the fridge and lose pungency within weeks. Powder keeps for about a year sealed; mix only what you need.
Substitutes¶
horseradish, freshly grated, with a pinch of English mustard powder is what most commercial "wasabi" is anyway. Tubed and powdered products are fine for everyday use — read the label to see how much real wasabi, if any, they contain.
Pairs well with¶
Raw fish, tuna, salmon, beef, soba noodles, avocado, soy sauce, rice vinegar, mayonnaise, cucumber, peas, ginger (pickled or fresh), sesame, shiso, spring onion and shichimi-togarashi.
Growing your own¶
Wasabi can be grown in cool, damp, shady spots, in the UK and similar climates, but it is not easy. It needs temperatures that stay roughly between 7 and 20°C, deep shade, constant moisture without waterlogging, and protection from slugs and aphids. A large pot of free-draining compost kept in a cool, shaded corner and watered with cold water can work. Expect to wait around 18 months to two years before harvesting a small stem; the leaves can be picked sooner.
Health and safety¶
📌 Check what you are eating
Because most "wasabi" paste and powder is made mainly from horseradish and mustard, people allergic to mustard — one of the 14 major allergens in the UK and EU — should check the label rather than assume it is safe. Wasabi-flavoured snacks and dressings commonly contain mustard too. See spice-allergies.
The rush of wasabi's heat is felt in the nose because isothiocyanates are volatile; it is intense but not harmful in normal amounts, and fades far faster than chilli heat.