Kale

• 1. Introduction

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  Kale is a leaf cabbage that spent most of the 20th century in the United States doing almost nothing that had to do with food. It sat on restaurant plates as a garnish, a bed of green meant to frame the meal rather than be eaten, and it only became a widely consumed vegetable there starting in the 1990s. What changed, and what exactly is kale doing in the vegetable world that made it worth eating in the first place? Kale belongs to the same species as headed cabbage, Brassica oleracea, but instead of forming a tight head, its central leaves stay loose, ranging from bumpy or curly to flat, and in colors from purple to green. This is a plant with roots in the eastern Mediterranean, a name borrowed from Northern Middle English, and a nutrient profile that eventually pulled it out of the garnish tray and onto the plate itself.

• 2. A Very Old Cabbage

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  Kale traces back to the eastern Mediterranean and Anatolia, where people were cultivating it for food by 2000 BCE at the latest. By the 4th century BC in Greece, both curly-leaved and flat-leaved varieties of cabbage already existed side by side, forms the Romans later called Sabellian kale and which are considered the ancestors of the kale grown today. Hard-heading cabbage shows up in the historical record of western Europe by the 13th century, and by the 14th century, English records draw a clear line between that hard-heading cabbage and the loose-leaf kale grown alongside it. Russian traders carried Russian kale into Canada and then the United States during the 19th century. American botanist David Fairchild is credited with introducing kale, among many other crops, to the United States after bringing it back from Croatia, an odd credit given that Fairchild personally disliked cabbages, kale included. In Croatia at the time, kale was grown widely mainly because it was cheap and easy, and because it could help desalinate soil.

• 3. Naming The Varieties

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  The English word kale descends from the Northern Middle English cale, related to the Scots word kail and the German Kohl, both meaning cabbage, and tracing further back to the Latin caulis. That shared root sits underneath a wide range of named forms. Curly-leaf kale includes Scots kale and blue curled kale, while bumpy-leaf kale is better known by its Italian name, cavolo nero, also called Tuscan kale, lacinato, or dinosaur kale. Other categories include sparkly-leaf kale, with a shiny, glossy surface, plain-leaf kale, such as red Russian and white Russian varieties, and a leaf-and-spear or feathery type that crosses curly-leaf and plain-leaf traits. One variety of rape kale earned the nickname "hungry gap," named for the stretch of winter in traditional agriculture when little else could be harvested, while an extra-tall variety goes by Jersey kale or cow cabbage. Kai-lan, or Chinese kale, is a cultivar commonly used in Chinese cooking, and in Portugal, a bumpy-leaved kale is called couve galega, or Galician kale.

• 4. Growing In The Cold

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  Derived from wild mustard, kale sits closer to wild cabbage than most of the domesticated forms of Brassica oleracea. It is typically grown as a biennial from seed, with a wide range of temperatures at which it will germinate, and it thrives specifically in winter, surviving temperatures as low as minus 15 degrees Celsius; a heavy frost can even make the leaves taste sweeter. That cold tolerance carried real commercial weight in one notable case: in 2012, Pizza Hut purchased approximately 14,000 pounds of kale purely for use as decoration on its salad bars. Ornamental varieties, grown for leaves in brilliant white, red, pink, lavender, blue, or violet at the center of the rosette, are technically as edible as any other kale, though generally regarded as less palatable, and kale leaves are increasingly used as an ingredient in vegetable and wedding bouquets.

• 5. What Kale Delivers Nutritionally

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  Raw kale is roughly 84 percent water, 9 percent carbohydrates, 4 percent protein, and 1 percent fat. A 100-gram serving of raw kale provides 207 kilojoules of food energy and 3.7 times the daily value of vitamin K, along with rich amounts, 20 percent or more of the daily value, of vitamin A, vitamin C, folate, and manganese. It also supplies good levels, in the 10 to 19 percent range, of riboflavin, pantothenic acid, vitamin B6, vitamin E, calcium, magnesium, and potassium. Boiling raw kale strips out most of these nutrients, though vitamins A, C, and K along with manganese remain substantial even after cooking. Kale also contains the carotenoids lutein and zeaxanthin, along with glucosinolate compounds such as glucoraphanin, which contributes to the formation of sulforaphane, a compound currently under preliminary research for potential health effects; boiling reduces glucosinolate levels, while steaming, microwaving, or stir-frying does not cause significant loss. The plant is also high in oxalic acid, which cooking can reduce, and contains polyphenols such as ferulic acid at levels that vary with environmental and genetic factors.

• 6. On Tables Around The World

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  In the Netherlands, a winter dish called boerenkoolstamppot mixes curly kale with mashed potatoes, sometimes with fried bacon, and is served alongside rookworst, a smoked sausage. Northern Germany marks winter with a tradition called Kohlfahrt, or "kale trip," a daytime hike through the woods that ends with a gathering at an inn or private home to eat kale, typically with bacon and a kale sausage called Kohlwurst; the region treats kale as a staple comfort food. In Italy, cavolo nero is an ingredient in the Tuscan soup ribollita, while in Portugal, caldo verde combines pureed potatoes, finely sliced kale, olive oil, and salt, sometimes with broth and sliced spicy sausage added. In Scotland, kale was so central to the traditional diet that the word became synonymous with food in some Scots dialects, giving rise to the phrase "off one's kail" to describe feeling too ill to eat. In Ireland, kale mixed with mashed potatoes forms colcannon, a dish especially popular on Halloween, sometimes served with sausages. In the United Kingdom, the government promoted kale cultivation, alongside other vegetables, during World War II through the Dig for Victory campaign. In Sri Lanka, kale is known as kola gova or ela gova and appears in a dish called kale mallung, served with rice almost everywhere on the island.

• 7. Kailyard And Kale Chips

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  The Kailyard school of Scottish writers, whose members included J. M. Barrie, creator of Peter Pan, took its name directly from the plant: kailyard means "kale field," and its authors wrote about traditional rural Scottish life. In his book Autumn in Kyle and the Charm of Cunninghame, writer Cuthbertson records that Kilmaurs, in East Ayrshire, was famous for its kale as an important local foodstuff, and tells of a neighboring village offering a generous price for Kilmaurs kale seeds. The locals accepted the deal but first gave the seeds a gentle roasting on a shovel over a coal fire, ensuring the buyers' crop would never germinate. Kale's culinary reputation has traveled a long way from that story and from its decades as American restaurant garnish: kale chips are now produced as a substitute for potato chips, and the plant has become one of the most popular greens in the United States, showing up regularly in salads and green smoothies.