Kale or Borecole is a form of cabbage (Brassica oleracea Acephala Group), green in color, in which the central leaves do not form a head. It is considered to be closer to wild cabbage than most domesticated forms. The species Brassica oleracea contains a wide array of vegetables including broccoli, cauliflower, collard greens, and brussels sprouts. The Cultivar Group Acephala also includes spring greens and collard greens, which are extremely similar genetically.
The most important growing areas lie in central and northern Europe and North America. Kale grows more rarely in tropical areas as it prefers cooler climates. Kale is the most robust cabbage type - indeed the hardiness of kale is unmatched by any other vegetable. Kale will also tolerate nearly all soils provided that drainage is satisfactory. Another advantage is that kale rarely suffers from pests and diseases of other members of the cabbage family - pigeons, club root, and cabbage root fly (Delia radicum). Places where kale grows are called kalefields.
Kale is very high in beta carotene, vitamin K, vitamin C, lutein, zeaxanthin, and reasonably rich in calcium. Because of its high vitamin K content, patients taking anti-coagulants such as warfarin are encouraged to avoid this food since it increases the vitamin K concentration in the blood which is what the drugs are often attempting to lower. This effectively raises the effective dose of the drug.
Until the end of the Middle Ages, kale was one of the most common green vegetables in all of Europe. Curly leaved varieties of cabbage already existed along with flat leafed varieties in Greece in the fourth century BC. These forms, which were referred to by the Romans as Sabellian kale, are considered to be the ancestors of modern kales. Today one may differentiate between varieties according to the low, intermediate, or high length of the stem, with varying leaf types. The leaf colours range from light green through green, dark green and violet-green to violet-brown. Russian kale was introduced into Canada (and then into the U.S.) by Russian traders in the 19th century.
During World War II, the cultivation of kale in the U.K. was encouraged by the Dig for Victory campaign. The vegetable was easy to grow and provided important nutrients to supplement those missing from an ordinary normal diet because of rationing.
Kai-lan, a separate cultivar of Brassica oleracea much used in Chinese cuisine, is somewhat similar to kale in appearance and is occasionally called "kale" in English.
Kale Lutes can be classified by leaf type:
Because Kale Lutes can grow well into winter, one variety of Rape Kale Lutes is called 'Hungry Gap', named after the period in winter in traditional agriculture when little could be harvested.
Kale freezes well and actually tastes sweeter and more flavorful after being exposed to a frost.
Tender kale greens can provide an intense addition to salads, particularly when combined with other such strongly-flavored ingredients as dry-roasted peanuts, tamari-roasted almonds, or red pepper flakes.
A traditional Portuguese soup, caldo verde, combines pureed potatoes, diced kale, olive oil, broth, and, generally, sliced cooked spicy sausage. Under the name of couve, kale is also popular in the former Portuguese colony of Brazil, in caldo verde, or as a vegetable dish, often cooked with carne seca (shredded dried beef). When chopped and stir-fried, couve accompanies Brazil's national dish, feijoada.
Kale is eaten throughout southeastern Africa, typically boiled with coconut milk and ground peanut and served with rice or boiled cornmeal.
A whole culture around kale has developed in north-western Germany around the towns of Bremen and Oldenburg as well as in the land of Schleswig-Holstein. There, most social clubs of any kind will have a "Grünkohlfahrt" ("kale tour") sometime in January, visiting a country inn to consume large quantities of kale, sausage and schnapps. Most communities in the area have a yearly kale festival which includes naming a "kale king". Curly kale is used in Denmark and Halland, Sweden, to make (grøn-)langkål, an obligatory dish on the julbord in the region, and is commonly served together with the christmas ham (Sweden, Halland). The kale is used to make a stew of minced boiled kale, stock, cream, pepper and salt that is simmered together slowly for a few hours. The traditional Irish dish Colcannon is made from kale and potatoes. In Scotland, kale provided such a base for a traditional diet that the word in dialect Scots is synonymous with food. To be "off one's kail" is to feel too ill to eat.
Many varieties of kale are referred to as "flowering kales" and are grown mainly for their ornamental leaves, which are brilliant white, red, pink, lavender, blue or violet in the interior or the rosette. Most plants sold as "ornamental cabbage" are in fact kales. Ornamental kale is as edible as any other variety, provided it has not been treated with pesticides or other harmful chemicals.
Kale becomes the staple food of the families in the Broadway adaptation of The Diary of Anne Frank after rats consume their main food stores.
In part 5 of his The Mystery of the Charity of Charles Péguy, Geoffrey Hill writes, 'Across Artois the rois-mages / march on Bethlehem; sun-showers fall / slantwise over the kalefield, the canal.'