Kale is one of the big harvests at the Penn State Horticulture Research Farm. The beautiful leaves, especially of the curly kale variety, provide an earthy flavor and more nutritional value for fewer calories than almost any other food around. Although it can be found in markets throughout the year, it is in season from the middle of winter through the beginning of spring, when it has a sweeter taste and is more widely available. We have been growing it for years in our high tunnels in the wintertime, as it is extremely hardy.
Kale (Brassica oleracea) is a leafy green vegetable that belongs to a group of vegetables that includes cabbage, collards and Brussels sprouts that have gained recent widespread attention due to their health-promoting, sulfur-containing phytonutrients. Kale is easy to grow and can thrive in colder temperatures; a light frost will produce especially sweet kale leaves. There are several varieties of kale — curly kale, ornamental kale and dinosaur (or Lacinato or Tuscan) kale, all of which differ in taste, texture and appearance.
Curly kale has ruffled leaves and a fibrous stalk and is usually deep green in color. It has a lively, pungent flavor with delicious bitter, peppery qualities. Ornamental kale is a more recently cultivated species that often is referred to as salad savoy. Its leaves may either be green, white or purple, and its stalks coalesce to form a loosely knit head. Ornamental kale has a more mellow flavor and tender texture.
Dinosaur kale features dark blue-green leaves that have an embossed texture. It has a slightly sweeter and more delicate taste than curly kale.
Like broccoli, cauliflower and collards, kale is a descendent of the wild cabbage, a plant thought to have originated in Asia Minor and brought to Europe around 600 B.C. by groups of Celtic wanderers. Curly kale played an important role in early European foods, having been a significant crop during ancient Roman times and a popular vegetable eaten by peasants in the Middle Ages. English settlers brought kale to the United States in the 17th century.
Both ornamental and dinosaur kale are much more recent varieties. Dinosaur kale was discovered in Italy in the late 19th century. Ornamental kale, originally a decorative garden plant, was first cultivated commercially in the 1980s in California.
Look for kale with firm, deeply colored leaves and moist, hardy stems. Kale should be displayed in a cool environment, because warm temperatures will cause it to wilt and will negatively affect its flavor. The leaves should look fresh, be unwilted, and be free from signs of browning, yellowing and small holes. Choose kale with smaller-sized leaves, because these will be tenderer and have a milder flavor than those with larger leaves.
To store, place kale in a plastic storage bag, removing as much of the air from the bag as possible. Store in the refrigerator, where it will keep for five days. The longer it is stored, the more bitter its flavor becomes. Do not wash kale before storing, because exposure to water encourages spoilage.
Kale also provides cholesterol-lowering benefits if it’s steamed. The fiber-related components in kale do a better job of binding together with bile acids in your digestive tract when they’ve been steamed. When this binding process takes place, it’s easier for bile acids to be excreted, and the result is a lowering of your cholesterol levels. Raw kale still has cholesterol-lowering ability — just not as much.
Kale’s risk-lowering benefits for cancer recently were extended to at least five different types of cancer, including bladder, breast, colon, ovary and prostate. Isothiocyanates made from glucosinolates in kale play a primary role in achieving these risk-lowering benefits. Kale is now recognized as providing comprehensive support for the body’s detoxification system. New research has shown that the ITCs made from kale’s glucosinolates can help regulate detox at a genetic level. In addition, researchers have identified more than 45 different flavonoids in kale. With kaempferol and quercetin heading the list, kale’s flavonoids combine both antioxidant and anti-inflammatory benefits in a way that gives kale a leading dietary role with respect to avoidance of chronic inflammation and oxidative stress.