G.Gaertn., B.Mey. & Scherb.
Horseradish (Armoracia rusticana, syn. Cochlearia armoracia) is a perennial plant of the Brassicaceae family (which also includes mustard, wasabi, broccoli, and cabbage). The plant is probably native to southeastern Europe and western Asia. It is now popular around the world. It grows up to 1.5 meters (5 feet) tall, and is cultivated primarily for its large, white, tapered root.
The intact horseradish root has hardly any aroma. When cut or grated, however, enzymes from the now-broken plant cells break down sinigrin (a glucosinolate) to produce allyl isothiocyanate (mustard oil), which irritates the mucous membranes of the sinuses and eyes. Once exposed to air (via grating) or heat, if not used immediately or mixed in vinegar, the grated mash darkens, loses its pungency, and becomes unpleasantly bitter-tasting.
Horseradish has been cultivated since antiquity. According to Greek mythology, the Delphic Oracle told Apollo that the horseradish was worth its weight in gold. Horseradish was known in Egypt in 1500 BC. Dioscorides listed horseradish under Thlaspi or Persicon; Cato discusses the plant in his treatises on agriculture, and a mural in Pompeii shows the plant. Horseradish is probably the plant mentioned by Pliny the Elder in his Natural History under the name of Amoracia, and recommended by him for its medicinal qualities, and possibly the Wild Radish, or raphanos agrios of the Greeks. The early Renaissance herbalists Pietro Andrea Mattioli and John Gerard showed it under Raphanus.
Both root and leaves were used as a medicine during the Middle Ages and the root was used as a condiment on meats in Germany, Scandinavia, and Britain. It was brought to North America during Colonial times.
William Turner mentions horseradish as Red Cole in his "Herbal" (1551–1568), but not as a condiment. In The Herball, or Generall Historie of Plantes (1597), John Gerard describes it under the name of raphanus rusticanus, stating that it occurs wild in several parts of England. After referring to its medicinal uses, he says:
|“||[T]he Horse Radish stamped with a little vinegar put thereto, is commonly used among the Germans for sauce to eat fish with and such like meats as we do mustard.||”|
The word horseradish is attested in English from the 1590s. It combines the word horse (formerly used as an adjective meaning "strong, large, or coarse") and the word radish. Despite the name, this plant is poisonous to horses.
Horseradish is perennial in hardiness zones 2–9 and can be grown as an annual in other zones, although not as successfully as in zones with both a long growing season and winter temperatures cold enough to ensure plant dormancy. After the first frost in the autumn kills the leaves, the root is dug and divided. The main root is harvested and one or more large offshoots of the main root are replanted to produce next year's crop. Horseradish left undisturbed in the garden spreads via underground shoots and can become invasive. Older roots left in the ground become woody, after which they are no longer culinarily useful, although older plants can be dug and re-divided to start new plants.
Pests and diseases 
Widely introduced by accident, "cabbageworms", the larvae of Pieris rapae, the Small White Butterfly, are a common caterpillar pest in horseradish. The adults are white butterflies with black spots on the forewings that are commonly seen flying around plants during the day. The caterpillars are velvety green with faint yellow stripes running lengthwise down the back and sides. Full grown caterpillars are about 1-inch (25 mm) in length. They move sluggishly when prodded. They overwinter in green pupal cases. Adults start appearing in gardens after the last frost and are a problem through the remainder of the growing season. There are three to five overlapping generations a year. Mature caterpillars chew large, ragged holes in the leaves leaving the large veins intact. Handpicking is an effective control strategy.
Culinary uses 
Cooks use the terms "horseradish" or "prepared horseradish" to refer to the grated root of the horseradish plant mixed with vinegar. Prepared horseradish is white to creamy-beige in colour. It will keep for months refrigerated but eventually will darken, indicating it is losing flavour and should be replaced. The leaves of the plant, while edible, are not commonly eaten, and are referred to as "horseradish greens".
Horseradish sauce 
Horseradish sauce made from grated horseradish root and vinegar is a popular condiment in the United Kingdom and in Poland. In the UK it is usually served with roast beef, often as part of a traditional Sunday roast, but can be used in a number of other dishes also, including sandwiches or salads. A variation of horseradish sauce, which in some cases may substitute the vinegar with other products like lemon juice or citric acid, is known in Germany as Tafelmeerrettich. Also popular in the UK is Tewkesbury mustard, a blend of mustard and grated horseradish originating in medieval times and mentioned by Shakespeare (Falstaff says: "his wit's as thick as Tewkesbury Mustard" in Henry IV Part II). A very similar mustard, called Krensenf or Meerrettichsenf, is popular in Austria and parts of Eastern Germany.
In the U.S., the term "horseradish sauce" refers to grated horseradish combined with mayonnaise or salad dressing. Prepared horseradish is a common ingredient in Bloody Mary cocktails and in cocktail sauce, and is used as a sauce or sandwich spread.
The distinctive pungent taste of horseradish is from the compound allyl isothiocyanate. Upon crushing the flesh of horseradish, the enzyme myrosinase is released and acts on the glucosinolates sinigrin and gluconasturtiin, which are precursors to the allyl isothiocyanate. The allyl isothiocyanate serves the plant as a natural defense against herbivores. Since allyl isothiocyanate is harmful to the plant itself, it is stored in the harmless form of the glucosinolate, separate from the myrosinase enzyme. When an animal chews the plant, the allyl isothiocyanate is released, repelling the animal. Allyl isothiocyanate is an unstable compound, degrading over the course of days at 37 °C. Because of this instability, horseradish sauces lack the pungency of the freshly crushed roots.
In Central and Eastern Europe horseradish is called khreyn (in various spellings like kren) in many Slavic languages, in Austria, in parts of Germany (where the other German name Meerrettich isn't used), in North-East Italy, and in Yiddish (כריין translitered as khreyn). There are two varieties of khreyn. "Red" khreyn is mixed with red beet (beetroot) and "white" khreyn contains no beet. It is popular in Ukraine (under the name of хрін, khrin), in Poland (under the name of chrzan), in Lithuania (krienai) in the Czech Republic (křen), in Russia (хрен, khren), in Hungary (torma), in Romania (hrean), in Bulgaria (хрян, khryan), and in Slovakia (under the name of chren). Having this on the table is a part of Christian Easter and Jewish Passover tradition in Eastern and Central Europe. A variety with red beet is called ćwikła z chrzanem or simply ćwikła in Poland. In Ashkenazi European Jewish cooking beet horseradish is commonly served with gefilte fish. Red beet with horseradish is also used as a salad served with lamb dishes at Easter called sfecla cu hrean in Transylvania and other Romanian regions. Horseradish (often grated and mixed with cream, hard-boiled eggs, or apples) is also a traditional Easter dish in Slovenia and in the adjacent Italian region of Friuli Venezia Giulia; it is used also in the other nearby Italian region of Veneto. In Croatia freshly grated horseradish(Croatian: Hren) is often eaten with boiled ham or beef. In Serbia ren is an essential condiment with cooked meat and freshly roasted suckling pig.
Relation to wasabi 
The Japanese condiment wasabi, although traditionally prepared from the wasabi plant, is now usually made with horseradish due to the scarcity of the wasabi plant. The Japanese botanical name for horseradish is seiyōwasabi (セイヨウワサビ, 西洋山葵), or "Western wasabi". Both plants are members of the family Brassicaceae.
Nutritional and biomedical uses 
Compounds found in horseradish have been widely studied for a plethora of health benefits. Horseradish contains volatile oils, notably mustard oil, which has antibacterial properties due to the presence of allyl isothiocyanate. Fresh, the plant also contains average 79.31 mg of vitamin C per 100 g of raw horseradish.
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- International Horseradish Festival
- Horseradish Information Council
- Herb Society of America Herb of the Year 2011