|Horseradish is a perennial plant of the Brassicaceae. 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 (4.9 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. Grated mash should be used immediately or preserved in vinegar for best flavor. Once exposed to air or heat it will begin to lose its pungency, darken in color, and become unpleasantly bitter tasting over time.