Wasabi (ワサビ or わさび（山葵）?, earlier 和佐比; Eutrema japonicum or Wasabia japonica) is a plant of the Brassicaceae family, which includes cabbages, horseradish, and mustard. It is also called Japanese horseradish, although horseradish is a different plant (which is generally used as a substitute for wasabi, due to the scarcity of the wasabi plant). Its stem is used as a condiment and has an extremely strong pungency more akin to hot mustard than the capsaicin in a chili pepper, producing vapours that stimulate the nasal passages more than the tongue.
The plant grows naturally along stream beds in mountain river valleys in Japan. The two main cultivars in the marketplace are E. japonicum ‘Daruma’ and ‘Mazuma’, but there are many others. The origin of wasabi cuisine has been clarified from the oldest historical records; it takes its rise in Nara prefecture, and more recently has seen a surge in popularity from the early 1990s to mid 2000s.
Real wasabi tastes more herbal than the horseradish stuff. It’s hot but doesn’t have a lingering, burning aftertaste. It’s supposed to taste smoother, cleaner and more “plant-like” than its commonly used substitute. The horseradish paste served in restaurants is harsher and not as fresh-tasting.
Wasabi is often grated with a metal oroshigane, but some prefer to use a more traditional tool made of dried sharkskin with fine skin on one side and coarse skin on the other. A hand-made grater with irregular teeth can also be used. If a shark-skin grater is unavailable, ceramic is usually preferred.
There are also numerous artificial cultivation facilities as far north as Hokkaido and as far south as Kyushu. As the demand for real wasabi is very high, Japan imports an amount from China, Taiwan, and New Zealand. In North America, a handful of companies and small farmers cultivate Wasabia japonica. A UK grower, believed to be the only producer in Europe, also grows wasabi in Dorset and Hampshire.
The two kanji characters “山” and “葵” do not correspond to their pronunciation: as such it is an example of gikun (meaning, not sound). The two characters actually refer to the mountain Asarum, as the plant’s leaves resemble those of a member of Asarum species, in addition to its ability to grow on shady hillsides. The word, in the form 和佐比, appeared in 918 in The Japanese Names of Medical Herbs (本草和名 Honzō Wamyō). Spelled in this way, the particular kanji are used for their phonetic values only, known as ateji (sound, not meaning – opposite of gikun).