large veins intact. Handpicking is an effective control strategy in home gardens. Production In the United States, horseradish is grown in several areas such as Eau Claire, Wisconsin, and Tule Lake, California. The most concentrated growth occurs in the Collinsville, Illinois region. 30,000 metric tonnes of horseradish are produced in Europe annually, of which Hungary produces 12,000, making it the biggest single producer. Culinary uses 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 enzyme myrosinase. 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 . Because of this instability, horseradish sauces lack the pungency of the freshly crushed roots. Cooks may use the terms "horseradish" or "prepared horseradish" to refer to the mashed (or grated) root of the horseradish plant mixed with vinegar. Prepared horseradish is white to creamy-beige in color. It can be stored for up to 3 months under refrigeration, but eventually will darken, indicating less flavour. The leaves of the plant are edible, either cooked or raw when young, with a flavor similar but weaker than the roots. On Passover, many Ashkenazi Jews (outside of Israel) use grated horseradish as a choice for Maror (bitter herbs) at the Passover Seder. Horseradish sauce Horseradish sauce made from grated horseradish root and vinegar is a common condiment in the United Kingdom, in Denmark (with sugar added) 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, 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 available 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