What 'wasabi' actually is — and what most 'wasabi' on overseas shelves is
Wasabia japonica (true wasabi) is a Brassicaceae plant native to Japan that grows along cold mountain streams. It produces a green rhizome with a distinctively delicate, complex pungency — sharp at first, then quickly dissipating, with floral and herbaceous notes. The active compounds (allyl isothiocyanate and similar isothiocyanates) are volatile and degrade within ~15 minutes of grating.
The 'wasabi' on most overseas sushi counters and supermarket shelves is not wasabi. It is typically a paste of grated horseradish (Armoracia rusticana — a European root), powdered mustard, and green food colouring. The pungency profile is harsher, longer-lasting, and lacks the aromatic complexity. This isn't a defect — it's a different ingredient with its own merits — but for buyers wanting to position 'real Japanese wasabi' the distinction matters.