Bean

A bean is the seed of any of several genera of the flowering plant family Fabaceae, used as a vegetable, as a source of protein, or as animal feed. In everyday usage, the term most often refers to the common bean, Phaseolus vulgaris, and closely related species such as the lima bean, runner bean, and tepary bean, but it is also applied broadly to many other edible legume seeds, including the soybean, chickpea, lentil, pea, cowpea, mung bean, adzuki bean, and fava bean. Beans are valued as staple foods because they are rich in protein, dietary fiber, complex carbohydrates, and micronutrients, and because legume crops can improve soil fertility through nitrogen fixation.

Description and terminology

The word bean does not correspond to a single botanical taxon. It is a culinary and agricultural term for edible seeds of leguminous plants, especially those harvested as dry grain or eaten as immature pods or seeds. In the food and trade sense, beans are often divided into dry beans, which are harvested when mature and dried, and green beans or snap beans, which are harvested while the pods are still tender. The term pulse is used by the Food and Agriculture Organization for annual leguminous crops harvested solely for dry grain, excluding green beans, green peas, and crops used mainly for oil extraction or sowing. Under this definition, most dry beans are pulses, while the soybean and peanut are not. Some plant products called beans, such as coffee beans, cocoa beans, castor beans, and vanilla beans, are not true beans in a botanical or culinary sense.

Botanical characteristics

Bean plants belong to the family Fabaceae, commonly called the legume, pea, or bean family. They may be herbaceous annuals, biennials, or perennials, depending on species and climate. Many cultivated beans are annuals with either a bushy, determinate growth habit or a climbing, indeterminate habit. The leaves of many Phaseolus species are trifoliate, while the flowers are typically papilionaceous, with a characteristic banner, wings, and keel. The fruit is a pod, botanically a legume, that usually splits open along two seams when mature.

Like most legumes, bean plants form symbiotic relationships with nitrogen-fixing bacteria, especially species of Rhizobium and Bradyrhizobium, which live in root nodules. These bacteria convert atmospheric nitrogen into ammonia, supplying the plant with nitrogen and reducing the need for synthetic nitrogen fertilizer. The seeds themselves vary widely in size, shape, and color, from small round peas to large kidney-shaped beans, and from white, cream, and yellow to red, brown, black, speckled, and mottled.

Major types of beans

Beans are produced from many species across several genera. The most widely consumed include:

• Common bean (Phaseolus vulgaris): includes black beans, kidney beans, pinto beans, navy beans, great northern beans, cannellini beans, cranberry beans, and flageolet beans.
• Lima bean (Phaseolus lunatus): also known as butter bean.
• Runner bean (Phaseolus coccineus): grown for edible pods and seeds.
• Tepary bean (Phaseolus acutifolius): a drought-tolerant species native to the southwestern United States and Mexico.
• Soybean (Glycine max): an oilseed and protein crop, used fresh as edamame and in many processed forms.
• Fava bean or broad bean (Vicia faba): an important crop in Mediterranean, Middle Eastern, and North African cuisines.
• Mung bean (Vigna radiata): used whole, split, sprouted, or ground into starch.
• Adzuki bean (Vigna angularis): widely used in East Asian sweet bean paste.
• Cowpea (Vigna unguiculata): includes the black-eyed pea and yardlong bean.
• Chickpea (Cicer arietinum): also known as garbanzo bean, used in hummus and many stews.
• Lentil (Lens culinaris): a small lens-shaped legume seed, usually classified as a pulse.
• Pea (Pisum sativum): consumed fresh as green peas or dried as split peas.
• Pigeon pea (Cajanus cajan): an important crop in South Asia, Africa, and Latin America.
• Hyacinth bean (Lablab purpureus): grown in tropical Africa and Asia.
• Winged bean (Psophocarpus tetragonolobus): a tropical species whose pods, leaves, and tubers are edible.

History and domestication

Beans were domesticated independently in several centers of agricultural origin. The common bean was domesticated at least twice: once in the Andes and once in Mesoamerica, giving rise to distinct gene pools. Remains of common beans have been found in archaeological sites in Peru and Mexico dating back thousands of years. The fava bean was one of the earliest domesticated crops of the ancient Mediterranean and Middle East. The soybean was domesticated in East Asia, likely from wild Glycine soja, and has been cultivated in China for several millennia. Cowpeas were domesticated in Africa, while chickpeas and lentils were among the founder crops of the Fertile Crescent.

The introduction of New World beans to Europe, Africa, and Asia after the Columbian exchange transformed diets around the world. In many regions, beans replaced or complemented older legumes such as fava beans, lentils, and chickpeas. The soybean later became a major global commodity, especially after the development of industrial oil and meal processing in the twentieth century.

Cultivation

Beans are grown in temperate, subtropical, and tropical regions. The common bean is a warm-season crop that is sensitive to frost; it grows best at temperatures between about 18 and 27 degrees Celsius. Planting is usually done after the last frost, with seeds placed directly in well-drained soil. Bush varieties mature in about 55 to 70 days, while pole varieties may require 70 to 110 days. Beans prefer a soil pH near neutral and benefit from adequate phosphorus and potassium, though many species require little nitrogen fertilizer because of nitrogen fixation.

Cropping systems vary widely. Beans are often intercropped with maize, cassava, coffee, or other crops. In traditional agriculture of the Americas, the common bean was one of the "Three Sisters" planted with maize and squash. Rotating beans with cereal crops helps break pest and disease cycles and improves soil nitrogen status. In modern large-scale agriculture, soybeans are commonly grown in rotation with maize or wheat, particularly in the Americas.

Global production of dry beans is in the tens of millions of tonnes annually. Major producers of dry common beans include India, Myanmar, Brazil, China, Mexico, and the United States. Soybean production is much larger, exceeding 300 million tonnes per year, with Brazil, the United States, and Argentina among the leading producers. Chickpeas, lentils, and dry peas are also significant pulse crops in South Asia, Canada, Australia, and the Mediterranean region.

Nutrition

Beans are nutrient-dense foods. A 100-gram serving of cooked common beans provides roughly 120 to 130 kilocalories, about 8 to 9 grams of protein, 5 to 7 grams of dietary fiber, and complex carbohydrates, with little fat. They contain folate, iron, magnesium, potassium, phosphorus, zinc, and several B vitamins. Colored beans, especially black and kidney beans, also contain polyphenols and other bioactive compounds with antioxidant activity.

The protein quality of beans is limited by low levels of the sulfur amino acids methionine and cysteine, but beans are rich in lysine, an amino acid that cereals lack in relative terms. Combining beans with cereal grains, such as rice, maize, or wheat, improves overall protein quality. Many traditional diets rely on such combinations, including rice and beans, maize and beans, and dal with wheat or rice.

Raw or improperly cooked beans contain antinutritional factors. Many dry beans, particularly kidney beans, contain lectins such as phytohaemagglutinin, which can cause severe gastrointestinal illness if beans are eaten raw or undercooked. Soaking and boiling at high temperature destroy most lectins. Beans also contain phytic acid, tannins, protease inhibitors, and oligosaccharides such as raffinose and stachyose. The oligosaccharides are not fully digested by human enzymes and are fermented by bacteria in the large intestine, which can cause flatulence. Fermentation, germination, soaking, and prolonged cooking reduce many antinutritional factors.

Health effects

Regular consumption of beans is associated with several health benefits. Epidemiological studies and clinical trials suggest that diets rich in beans may help lower LDL cholesterol, improve blood glucose control, reduce blood pressure, and support healthy body weight. Beans have a low glycemic index because their starch is digested slowly, and their fiber and protein promote satiety. Dietary guidelines in many countries recommend legumes as part of a healthy eating pattern, often as a plant-based protein alternative to meat.

Beans are also important for food security and nutrition in low-income regions, where they provide an inexpensive source of protein, iron, zinc, and folate. However, the bioavailability of iron and zinc from beans can be reduced by phytates. Processing methods such as soaking, fermenting, and sprouting can improve mineral absorption. Some individuals with favism, a genetic deficiency of the enzyme glucose-6-phosphate dehydrogenase, must avoid fava beans because certain compounds in them can trigger hemolytic anemia.

Culinary uses

Beans are used in an enormous variety of culinary preparations around the world. Dry beans are typically soaked, rinsed, and then simmered until tender. They are used in soups, stews, salads, casseroles, spreads, and fillings. Famous bean dishes include Boston baked beans, French cassoulet, Brazilian feijoada, Mexican refried beans, Caribbean rice and peas, Cuban black beans, Italian pasta e fagioli, Greek fasolada, and Spanish fabada.

Green beans and other immature pods are eaten steamed, boiled, stir-fried, pickled, or in casseroles. Soybeans are consumed fresh as edamame, or processed into tofu, tempeh, miso, soy sauce, soy milk, and soybean oil. Mung beans are sprouted for bean sprouts or ground into starch for cellophane noodles. Adzuki beans are often sweetened and made into red bean paste used in East Asian desserts. Chickpeas are used in hummus, falafel, and curries. Lentils are stewed into dals and soups.

Processing and products

Beans are sold fresh, dried, canned, frozen, and as processed ingredients. Canned beans are often pre-cooked and convenient, though they may contain added sodium and, in some cases, additives. Dried beans have a long shelf life but require soaking and cooking. Bean flours are made from various species and are used in gluten-free baking, batters, and traditional foods. In West Africa, cowpea flour is used for fritters and steamed pastes. In East Asia, mung bean starch is used for noodles and dessert gels.

Soybeans are among the most intensively processed agricultural commodities. Industrial crushing separates soybean oil from protein-rich meal, which is used mainly as animal feed. Further processing of soybeans produces soy protein isolates, concentrates, texturized vegetable protein, tofu, soy milk, miso, tempeh, natto, and soy sauce. Fermented soybean products such as miso, tempeh, and natto are distinctive for their flavors, microbial transformations, and improved digestibility.

Economic importance

Beans are economically significant as food crops, cash crops, and rotation crops. Dry pulses are important in regional trade, especially in South Asia, Latin America, East Africa, and parts of Europe. Smallholder farmers in many developing countries grow beans for subsistence and local markets. The common bean is a major source of dietary protein in parts of Latin America and eastern and southern Africa, where it is sometimes called "the poor man's meat."

The soybean has a uniquely large role in the global agricultural economy. It is the world's largest source of vegetable oil and a major source of high-protein animal feed. Soybean meal is central to poultry, pork, and aquaculture production. International trade in soybeans, particularly from Brazil and the United States to China and Europe, has major economic and environmental implications, including concerns about deforestation and land-use change in South America.

Pests, diseases, and abiotic stresses

Beans are affected by a wide range of pests and diseases. Common insect pests include bean beetles, bean weevils, aphids, leafhoppers, whiteflies, and pod borers. Stored beans may be damaged by bruchid beetles. Major diseases of common bean include anthracnose, common bacterial blight, halo blight, rust, angular leaf spot, white mold, and bean common mosaic virus. Root rots and damping-off caused by soil fungi can be severe in wet conditions.

Soybeans are affected by soybean cyst nematode, sudden death syndrome, Asian soybean rust, phytophthora root rot, and several viral diseases. Integrated pest management strategies include resistant varieties, crop rotation, sanitation, biological control, and the careful use of pesticides. Abiotic stresses such as drought, heat, waterlogging, and soil acidity limit bean production in many regions. Breeding programs have developed improved varieties with greater tolerance to drought, low phosphorus, and major diseases.

Cultural and social significance

Beans have deep cultural meaning in many societies. In Mesoamerica and North America, the intercropping of maize, beans, and squash, known as the Three Sisters, has long been a foundational agricultural and spiritual practice among Indigenous peoples. In many Latin American countries, beans are a daily staple and a symbol of home cooking and national identity. Cowpeas and black-eyed peas are traditional in the cuisine of West Africa and the African diaspora, especially in the southern United States, where eating black-eyed peas on New Year's Day is associated with good luck.

In Asia, soybeans and mung beans are central to fermented foods, sweets, and temple and festival dishes. In Europe and the Mediterranean, fava beans, lentils, and chickpeas have been cultivated and eaten since antiquity. Because beans are inexpensive, storable, and nutritious, they have often been associated with peasant food, but in modern cuisine they are also celebrated as part of plant-based and sustainable diets. Their low environmental footprint relative to many animal protein sources has made beans a focus of global discussions on sustainable food systems and climate-friendly nutrition.