What Is Wasabi Made Of: The Real Root and What's in the Tube
What is wasabi made of: real wasabi paste is grated from the rhizome of Eutrema japonicum, which grows in the flowing water of mountain streams. Tubes and inexpensive restaurants usually sell not this, but a paste made from horseradish with green coloring. You can tell one from the other by the labeling: Japanese standards separately name real wasabi and just wasabi — it's not a fake, but two different products under similar names.
All the frequent questions about wasabi boil down to one — what is it actually made of — and the answer doesn't match what's on the plate in most restaurants. Let's break down how the real root differs from what's sold in tubes, why the heat hits your nose rather than burning your tongue, and why a shark skin grater is used for it. Separately — where real wasabi grows and why it's not a quick harvest.
A mountain stream rhizome, not a root in the usual sense
For real wasabi, what's eaten is the thickened rhizome — more precisely, a modified stem of a plant that lives not in ordinary soil, but right in cold mountain streams with a constant flow of water. It's grated on a grater immediately before serving: the heat and aroma appear at the moment of grating and almost completely disappear within a few minutes after.
Why it can't be grated in advance
The sharp taste and smell of wasabi are not a permanent property of the rhizome, but the result of its cells being broken down. While the root is whole, it barely smells; all the power appears only at the moment it's grated, and quickly dissipates. That's why in restaurants that serve real wasabi, it's grated in portions, not in advance for the whole day.
葵 — значение: mallow, Tokugawa clan crest — онъёми: キ — кунъёми: あおい — 12 штрих(ов). 葵 — 'mallow': in the word 山葵 this is the second character, 山 'mountain' plus 葵 'mallow' — literally 'mountain mallow', though botanically wasabi has nothing to do with mallows, it's a cruciferous plant. The same character is known from the crest of the Tokugawa clan — 三つ葉葵, 'three mallow leaves'.
Write 葵 along the guides — the second character in the word 山葵, which in the botanical name calls the plant 'mountain mallow'.
The tube and the real root are most often different plants
Most of what's sold in tubes and served in inexpensive restaurants is made not from Eutrema japonicum, but from 西洋わさび (seiyō wasabi) — ordinary horseradish colored green. This is not a fake in the legal sense: Japan has labeling rules that explicitly separate real wasabi and its horseradish substitute under a similar name.
What the label 本わさび使用 means
According to the unified standard of the Japan Wasabi Processors Association (日本加工わさび協会), the label 本わさび使用 ('real wasabi used') can only be applied if the share of the real root in the composition is at least half. If the share is lower, the product is labeled more softly — 本わさび入り, 'with real wasabi added', and without either label there's no real root in the tube at all.
Why wasabi hits your nose rather than burning your tongue like pepper
Pepper heat stays on the tongue, while wasabi's pungency almost immediately rises into the nasopharynx and fades just as quickly — this is due to volatile compounds that form only when the rhizome's cells are broken down. While the cells are intact, harmless compounds lie separately in them; the enzyme triggers the reaction only when the tissue is grated into a paste.
Why a shark skin grater is needed
That's why the shark skin grater (鮫皮おろし) was invented: its surface is finer and softer than a metal one, and it breaks down the rhizome's cells more gently, without squeezing out excess juice. A metal grater cuts more coarsely, and some of the aroma is lost even before serving — that's why restaurants with real wasabi almost always use shark skin.
Shizuoka and Nagano — two dissimilar ways of growing
Real wasabi is grown in few places: the main regions are the Izu Peninsula in Shizuoka Prefecture and Azumino in Nagano Prefecture. In Izu, wasabi is grown on terraced beds lined with stone since the late 19th century — this allows water and oxygen to pass through the entire bed and protects the root from disease. In Azumino, a different method is used: planting directly on a flat sandy plot where snowmelt water from the Northern Alps constantly flows out.
Why the real root is expensive
The plant needs cold flowing water, shade, and a constant temperature — few places in Japan meet these conditions, and it takes a couple of years to grow a marketable root, not one season. All this makes real wasabi a labor-intensive and slow crop, and that's why it costs more than horseradish with coloring, not just because of the rarity of the name.
FAQ
- What is wasabi made of?
- Real wasabi is the thickened rhizome of the plant Eutrema japonicum, which grows in the cold flowing water of mountain streams and is grated right before serving. But tubes and inexpensive restaurants more often sell a paste made from horseradish with green coloring, not from this plant.
- What's actually in a tube of wasabi?
- Most often — a paste made from 西洋わさび, ordinary horseradish, colored green, not from the real rhizome of Eutrema japonicum. This is not a fake in the legal sense: Japan has labeling that honestly separates products with real wasabi and without it, it's just that the names are similar.
- How does real wasabi differ from horseradish?
- They are different plants from different families, though both belong to the cruciferous family and both are pungent. Real wasabi grows in the flowing water of mountain streams and requires years of care, while horseradish is undemanding and grows in almost any soil. Hence the difference in price, and the fact that what's most often sold as wasabi is actually horseradish.
- Why does wasabi hit your nose?
- The pungent volatile compounds form only when the rhizome's cells are broken down — that is, at the moment of grating, not in advance. These compounds rise into the nasopharynx rather than lingering on the tongue like pepper's capsaicin, so the sensation is sharp but short and fades almost immediately.
- Why is wasabi grated on a shark skin grater?
- The surface of shark skin is finer and softer than a metal grater, so it breaks down the rhizome's cells more gently, without squeezing out excess juice and without destroying the aroma. A metal grater cuts more coarsely, and some of the pungency and smell is lost even before the dish is served.
- Where is real wasabi grown?
- The main regions are the Izu Peninsula in Shizuoka Prefecture and Azumino in Nagano Prefecture. In Izu, wasabi has been grown on stone terraced beds since the late 19th century, while in Azumino flat plots with a constant flow of snowmelt water from the mountains are used for planting. The plant needs cold flowing water and shade, so there are few suitable places.
Sources
Updated: 2026-09-21