Wasabi (ワサビ or わさび(山葵, earlier 和佐比); Eutrema japonicum or Wasabia japonica) or Japanese horseradish is a plant of the Brassicaceae family, which also includes horseradish and mustard in other genera. A paste made from its ground rhizomes is used as a pungent condiment for sushi and other foods. It is similar in taste to hot mustard or horseradish rather than chili peppers in that it stimulates the nose 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 oldest record of wasabi as a food dates to the 8th century CE. The popularity of wasabi in English-speaking countries has tracked that of sushi, growing steadily starting in about 1980.
Due to issues that limit the Japanese Wasabi plant's mass cultivation and thus increases its price and decreases availability, outside of Japan the Western Horseradish plant is generally used in place of the Japanese Horseradish. This version is commonly referred to as "Western Wasabi" in Japan.
In some high-end restaurants, the paste is prepared when the customer orders, and is made using a grater to grate the stem; once the paste is prepared, it loses flavor in 15 minutes if left uncovered. In sushi preparation, sushi chefs usually put the wasabi between the fish and the rice because covering wasabi until served preserves its flavor.
Fresh wasabi leaves can be eaten, having the spicy flavor of wasabi stems.
Legumes (peanuts, soybeans, or peas) may be roasted or fried, then coated with wasabi powder mixed with sugar, salt, or oil and eaten as a crunchy snack. In Japan, it's called 'wasabi-mame'. 'mame' means bean.
Wasabi crop growing on Japan's Izu Peninsula
Wasabi favours growing conditions that restrict its wide cultivation (among other things, it is quite intolerant of direct sunlight, requires an air temperature between 8°C (46°F) and 20 °C (70°F), and prefers high humidity in summer). This makes it impossible for growers to fully satisfy commercial demand, which makes wasabi quite expensive. Therefore, outside Japan, it is rare to find real wasabi plants. Due to its high cost, a common substitute is a mixture of horseradish, mustard, starch, and green food coloring or spinach powder. Often packages are labeled as wasabi while the ingredients do not actually include any part of the wasabi plant. The primary difference between the two is color, with Wasabi being naturally green. In Japan, horseradish is referred to as seiyō wasabi (西洋わさび, "western wasabi"). In the United States, true wasabi is generally found only at specialty grocers and high-end restaurants.
The chemical in wasabi that provides for its initial pungency is the volatile allyl isothiocyanate, which is produced by hydrolysis of natural thioglucosides (conjugates of the sugar glucose, and sulfur-containing organic compounds); the hydrolysis reaction is catalyzed by myrosinase and occurs when the enzyme is released on cell rupture caused by maceration – e.g., grating – of the plant. The same compound is responsible for the pungency of horseradish and mustard. Allyl isothiocyanate can also be released when the wasabi plants have been damaged, because it is being used as a defense mechanism.
The unique flavor of wasabi is a result of complex chemical mixtures from the broken cells of the plant, including those resulting from the hydrolysis of thioglucosides into glucose and methylthioalkyl isothiocyanates:
- 7-methylthioheptyl isothiocyanate
- 8-methylthiooctyl isothiocyanate
Because the burning sensations of wasabi are not oil-based, they are short-lived compared to the effects of capsaicin in chili peppers, and are washed away with more food or liquid. The sensation is felt primarily in the nasal passage and can be quite painful depending on the amount consumed. Inhaling or sniffing wasabi vapor has an effect like smelling salts, a property exploited by researchers attempting to create a smoke alarm for the deaf. One deaf subject participating in a test of the prototype awoke within 10 seconds of wasabi vapor sprayed into his sleeping chamber. The 2011 Ig Nobel Prize in Chemistry was awarded to the researchers for determining the ideal density of airborne wasabi to wake people in the event of an emergency.
Wasabi is normally consumed in such small quantities that its nutritional value is negligible. The major constituents of raw wasabi root are carbohydrates (46%), water (32%), and fat (11%).
Few places are suitable for large-scale wasabi cultivation, and cultivation is difficult even in ideal conditions. In Japan, wasabi is cultivated mainly in these regions:
- Izu Peninsula, in Shizuoka Prefecture
- Nagano Prefecture including the Daio Wasabi Farm in Azumino; a popular tourist attraction and the world's largest commercial wasabi farm.
- Iwate Prefecture
- Shimane Prefecture known as its Hikimi wasabi
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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 Taiwan, Korea, Israel, Thailand and New Zealand. In North America, a handful of companies and small farmers cultivate Wasabia japonica. In Europe wasabi is grown commercially in Iceland and the UK.
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.
The two kanji characters "山" and "葵" do not correspond to their pronunciation: as such it is an example of gikun (related to meaning, not the 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).
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