Alys Fowler: Horseradish

Fresh horseradish, unlike the preserved stuff, has the devil inside it.If you've ever grated fresh horseradish you'll know it has the devil inside it. The roots contain a compound that when broken down releases wild, volatile mustard oils that will have you weeping and spluttering. It's the plant's defence against herbivores. If you intend to grate a lot, it's well worth donning goggles and opening all available windows.This compound is harmful to the plant as well as the eater, and is stored in a stable state until the plant is munched. As the cells are macerated, the plant releases an enzyme that causes the compound to break down. It is very unstable and quickly starts to degrade, which is why fresh grated horseradish will turn dark and bitter if left unpreserved. For this reason, if you care for a kick, preserved sauces are never the way to go. They will always lack the pungency of the freshly crushed root.Horseradish (Armoracia rusticana) is easy to grow - perhaps too easy, as anyone who's left it unharvested will find out. It's a clump-forming perennial that becomes invasive if not regularly harvested. It will grow anywhere damp and doesn't mind partial shade, but for fat, straight roots, you need good fertile soil rich in well-rotted organic matter.Old, neglected plants tend to have woody roots that aren't much use in the kitchen, so split clumps every three years. This can be done now if the soil is workable, or take root cuttings (pencil thickness, 10cm long) in spring. If you dig up your plant, any fragments of root that remain will resprout. It's pretty hard to get rid of a horseradish. When replanting, add well-rotted compost or manure.Many books will tell you the roots need to be harvested in early winter and then can be stored in damp sand somewhere cool and frost-free. In reality, unless you want huge quantities, harvest the roots any time you can dig (though in spring the young roots will be thin). Thin out any very small or crooked roots as you go, otherwise the plant becomes overcrowded.The leaves are edible, though they toughen with age. The tender spring leaves are good in salads, imparting a hint of spice. Or steam them like mustard or spinach (prolonged cooking will break down the heat, but leave them bitter).The leaves are often added to fermented pickles to keep them crunchy. Still, I think the best use of fresh horseradish is to shave a little root into vodka and let it sit for a hour or so before making a bloody mary. It makes for a wonderful, complex heat beneath the tomato juice.'It's pretty hard to get rid of a horseradish.' Photograph: Getty Images