Red bean
The red bean, commonly known as the adzuki bean (Vigna angularis), is an annual bushy herb in the legume family Fabaceae, characterized by trifoliate leaves, yellow flowers, and cylindrical pods containing 4–12 small, reddish-brown seeds.[1] Native to East Asia, with its wild ancestor (V. angularis var. nipponensis) distributed across the region, the earliest archaeological evidence dates to approximately 9000 BP in China, while genomic studies suggest a single domestication origin in central Japan around 3,000–5,000 years ago.[2][3] It has been cultivated for thousands of years, with major production in China (approximately 350,000 metric tons as of 2024/25), Japan (approximately 100,000 tons annually in recent years, though consumption exceeds 140,000 tons), South Korea, Taiwan, and increasingly in the United States, Canada, Australia, and India's northeastern hills.[4][1] The plant typically reaches 30–90 cm in height and thrives in warm climates, intolerant of low temperatures. In culinary traditions, particularly in East Asian cuisine, adzuki beans are prized for their sweet, nutty flavor and are most notably processed into red bean paste (anko) for use in desserts such as Japanese manju buns, mochi, tangyuan dumplings in Chinese cuisine, and various porridges, jellies, ice creams, and adzuki rice blends.[1] The beans also serve practical agricultural roles, including as forage, green manure, and for soil conservation due to their nitrogen-fixing properties as a legume.[5] Nutritionally, raw adzuki beans are dense in energy at 329 kcal per 100 g, providing 19.87 g of protein, 62.9 g of carbohydrates (including 12.7 g of dietary fiber), and essential micronutrients such as 622 µg of folate (155% of the daily value), 1,254 mg of potassium, 127 mg of magnesium, 381 mg of phosphorus, and 4.98 mg of iron.[6] They contain bioactive compounds like phenolic compounds and flavonoids, contributing antioxidant properties, and have been used medicinally in traditional Chinese practices as a diuretic for conditions such as dropsy.[1]Botanical Overview
Taxonomy and Classification
The red bean, scientifically known as Vigna angularis (Willd.) Ohwi & Ohashi, belongs to the family Fabaceae and the subfamily Faboideae, within the subgenus Ceratotropis of the genus Vigna.[7][8] This classification places it among other economically important legumes, reflecting its shared characteristics such as nitrogen-fixing nodules and pod-bearing fruits typical of the Fabaceae family.[1] The species encompasses two primary varieties: the cultivated form, V. angularis var. angularis, which features larger seeds and non-shattering pods adapted for human harvest, and the wild progenitor, V. angularis var. nipponensis, characterized by smaller seeds, shattering pods, and greater environmental resilience.[1] Genetic divergence between these varieties, estimated at approximately 50,000 years ago, predates archaeological evidence of domestication and is supported by genome sequencing analyses showing purifying selection and structural variations.[9][5] Evolutionary studies position V. angularis closely related to other Asian Vigna species in the subgenus Ceratotropis, including the mung bean (Vigna radiata) and black gram (Vigna mungo), with which it shares a common ancestor diverging from more distant relatives like cowpea (Vigna unguiculata) around 8–15 million years ago.[10] These relations are evidenced by comparative genomics revealing conserved synteny and similar domestication syndromes, such as reduced seed dormancy and altered pod dehiscence.[11] Common names for V. angularis include adzuki bean and azuki bean, derived from the Japanese term "azuki" meaning "small bean," reflecting its compact seed size relative to other legumes like soybean; in Chinese, it is known as "hong dou," literally "red bean," due to the predominant red seed coat in cultivated varieties.[12] It is also sometimes called red mung bean to distinguish it from the green-seeded mung bean, though this can cause confusion given their taxonomic proximity.[1]Physical Description
The red bean plant (Vigna angularis), an annual herbaceous legume, exhibits a bushy and erect growth habit, typically reaching 25–90 cm in height, though it can occasionally adopt a slightly vining or prostrate form.[7] Its leaves are trifoliolate, with ovate leaflets measuring 3–13 cm long and 2–9 cm wide, featuring surfaces that range from glabrous to sparsely pubescent; these are borne on petioles 2–10 cm in length with short petiolules of 1–3 mm.[7] The flowers are small, measuring 5–8 mm in length, and display yellow to orange coloration within papilionaceous corollas; they are self-pollinating and arranged in racemes of 1–10 blooms on peduncles 1–15 cm long, typically appearing during summer months from June to September.[7][13] The fruit consists of linear to cylindrical pods, 6–13 cm long and 4–6 mm wide, which are glabrous or sparsely hairy and contain 4–10 seeds each.[7] The seeds are small and cylindrical, approximately 2–5 mm long, 2–3 mm wide, and 1.5–2.5 mm thick, encased in a smooth hull that is characteristically red to maroon with a prominent white hilum; the cotyledons possess a high starch content, ranging from 44.55% to 53.92% of the seed's dry weight.[7][1][7] Among cultivars, seed colors vary to include brown, black, white, gray, or mottled patterns, with corresponding differences in size and hull texture.[7]History and Origin
Domestication
The adzuki bean (Vigna angularis), commonly referred to as red bean, is native to East Asia, where its wild progenitor (V. angularis var. nipponensis) is distributed across regions including Japan, Korea, southern China, and extending into the Himalayan foothills of Bhutan, Nepal, and northern India.[14] Recent genomic research points to a single domestication event in central Japan during the Jōmon period, approximately 3,000 to 5,000 years ago (ca. 1000–3000 BCE), rather than multiple independent origins, with subsequent hybridization incorporating genetic diversity from Chinese wild populations.[3] Archaeological evidence documents early human interaction with adzuki beans in China, including charred remains from the Xiaogao site in Shandong province dated to 9,000–8,000 years ago (ca. 7000–6000 BCE), during the Early Neolithic period; these small seeds, with an average volume of 5.8 mm³, suggest initial gathering or incipient cultivation within a multicropping system alongside millet, rice, and soybeans, predating the Yangshao culture.[2] In Japan, Jōmon period sites (ca. 4000–2000 BCE) yield the earliest indicators of domestication, with morphological changes such as larger seed size and reduced pod shattering evident in archaeobotanical assemblages, reflecting human selection for non-dispersing varieties suitable for harvesting.[3] Genetic studies confirm domestication syndrome traits, including diminished pod dehiscence through a frameshift mutation in the VaMYB26 gene, enhanced seed size, and uniform red coloration via mutations in VaANR1 (for proanthocyanidin reduction) and VaPAP1 (eliminating mottled patterns), which distinguish cultivated from wild forms.[3] Analyses using simple sequence repeat (SSR) markers reveal a genetic bottleneck associated with this single domestication origin, followed by elevated diversity in cultivated lines due to introgression and regional adaptation.[15] Early domesticated adzuki beans served primarily as a pulse crop, valued for their protein-rich seeds in human diets and integrated into Jōmon subsistence economies that emphasized foraging and semi-intensive plant management.[2][3]Spread and Historical Cultivation
The spread of red beans (Vigna angularis), commonly known as adzuki beans, beyond their East Asian origins occurred through ancient trade networks, facilitating their adoption in neighboring regions. Following initial domestication in central Japan around 3,000 to 5,000 years ago, with subsequent hybridization incorporating genetic diversity from Chinese wild populations, cultivated varieties expanded to the Asian mainland, with archaeological evidence of carbonized seeds from early sites dating back to ~4800 cal BP during the Chulmun period, and later in sites such as the Kudara ruins (~700 CE), often alongside rice and soybeans.[16][14] Trade routes, including those akin to the early Silk Road exchanges, contributed to dissemination from China to Korea and Southeast Asia, where adzuki beans integrated into local agricultural systems by the late first millennium BCE, supported by findings of early Neolithic multicropping with millet, rice, and soybeans in eastern China dating to 9,000–8,000 years ago.[12][17][2] Historical records document adzuki beans' early recognition in Chinese texts as a medicinal plant, with mentions in the Shennong Bencao Jing (compiled around 100 CE but attributed to traditions from ~200 BCE) describing it as "hsiao tou" or small red bean, classified as a middle-grade drug that eliminates water, expels swellings, and smooths the skin.[12] In medieval Japan, cultivation intensified for both practical and ceremonial purposes; the Engi-shiki (927 CE) recommended adzuki beans as a taxable crop, while they featured prominently in festivals through dishes like sekihan (red rice with beans), symbolizing auspiciousness due to the beans' red color believed to ward off evil.[12] By the Tokugawa period (1649 edict), adzuki cultivation was mandated between rice fields to enhance soil fertility and provide a reliable harvest for confections and rituals.[12] European interest in adzuki beans emerged in the 19th century primarily as a potential forage crop, with early introductions including trials in France in 1882 by Vilmorin-Andrieux and in Kansas in 1890 by agronomist C.C. Georgeson, who noted its suitability for green manure but limited yield for fodder in temperate climates.[12] The beans reached the Americas in the 19th century via Japanese immigrants, who brought seeds to Hawaii and the mainland United States as part of their agricultural practices; a key event was the 1878 introduction to California, where initial plantings supported small-scale farming among immigrant communities.[12] Post-World War II global trade expanded significantly due to Asian diaspora networks, particularly Japanese and Chinese communities in North America and Europe, which popularized adzuki beans through macrobiotic diets and ethnic cuisines, boosting imports and consumption from 440,000 tons annually in Japan by 1979 to wider international markets.[12] In the 20th century, breeding programs in Japan and China focused on improving yield, disease resistance, and seed quality to meet growing demand; Japan's efforts, led by institutions like the National Agriculture and Food Research Organization, developed high-yielding varieties through conventional selection since the 1920s, while China's programs emphasized diverse landraces for regional adaptation, resulting in cultivars with larger seeds and non-shattering pods by the mid-century.[18][19]Cultivation and Production
Growing Conditions
Red beans, scientifically known as Vigna angularis, thrive in warm temperate climates with optimal daytime temperatures ranging from 20 to 30°C, though they can tolerate a broader range of 15 to 32°C during active growth.[20][21] The plants are highly frost-sensitive and require soil temperatures above 15°C for germination, making them unsuitable for regions with prolonged cold spells or early/late frosts.[20][22] As short-day plants, they exhibit enhanced flowering under photoperiods of 12 to 14 hours, which influences their adaptation to temperate latitudes.[20][23] For soil, red beans prefer well-drained sandy loam or loamy textures rich in organic matter, with a pH range of 5.5 to 6.5 to support optimal nutrient uptake.[24][25] Poor drainage can lead to root rot, while heavy clay soils hinder root development.[22] As nitrogen-fixing legumes, they form symbiotic relationships with rhizobia bacteria in root nodules, reducing the need for external nitrogen fertilizers, though inoculation of seeds is recommended in soils low in native rhizobia.[24][26] Planting typically involves direct sowing seeds at a depth of 2 to 3 cm in rows spaced 30 to 45 cm apart, with in-row spacing of 5 to 10 cm to achieve a plant density of about 100,000 to 150,000 plants per hectare.[22][27] Narrower row spacings promote taller plants for easier mechanical harvest. Irrigation requirements total 300 to 500 mm of water over the growing season, with consistent moisture during flowering and pod fill to prevent stress, though the crop shows moderate drought tolerance once established.[28][29] Common pests such as aphids and pod borers (Maruca vitrata) can damage foliage and pods; management includes monitoring for early infestations, using insecticidal soaps for aphids, and targeted insecticides applied before larvae enter pods.[30][31][32] Harvesting occurs 90 to 120 days after planting, when pods dry to a tan color and rattle with mature seeds, typically in mid- to late autumn depending on sowing date.[29][27] Plants are cut or pulled, dried in the field, and threshed to separate seeds from pods, with yields optimized by timely harvest to avoid pod shatter.[20][7]Major Producing Regions
China is the world's leading producer of adzuki beans (Vigna angularis), commonly known as red beans, accounting for the majority of global output with an estimated 350,000 metric tons in the 2024/25 marketing year, representing approximately 60-70% of total production.[4] This dominance stems from extensive cultivation in provinces like Heilongjiang and Jilin, where the crop benefits from suitable temperate climates and established farming infrastructure.[3] Japan follows as the second-largest producer, yielding around 100,000 metric tons annually, primarily in Hokkaido, though domestic production meets only a portion of its high consumption needs.[33] South Korea and Taiwan contribute smaller but significant shares, with production estimated at 20,000–25,000 metric tons in South Korea, focused in regions like Gangwon Province.[1] Emerging production areas include Australia, Canada, the United States, and India. In Australia, annual production remains limited at under 5,000 metric tons, constrained by agronomic challenges but aided by favorable southern climates.[34] Canada produces a significant volume, with exports reaching approximately 31,000 metric tons in 2023, mainly to Japan.[35] The U.S., mainly through California and Idaho farms, exports approximately 10,000–12,000 metric tons yearly to Asian markets.[36] In India, cultivation is increasing in the northeastern hills. Average yields across major regions range from 1 to 2 metric tons per hectare, influenced by soil type and irrigation, with varietal improvements—such as disease-resistant hybrids—boosting output by up to 20% since 2010 in key East Asian areas.[37][38] Global trade in adzuki beans reached a value of about $188 million USD in 2023, projected to approach $200 million in 2024, driven by demand for traditional foods.[36] Japan, a major importer, supplements domestic shortfalls with imports totaling approximately 29,000 metric tons as of 2023, sourcing about 40% from China and 53% from Canada.[39] Economic factors, including fluctuating prices and export quotas, shape production decisions, with China's exports alone exceeding 38,000 metric tons in 2023/24.[4] Production faces challenges from climate change in East Asia, including erratic rainfall and rising temperatures that reduce yields by 10-15% in affected seasons, prompting shifts toward resilient varieties.[5] Sustainable practices, such as crop rotation with cereals to enhance soil health and nitrogen fixation, are increasingly adopted to mitigate these impacts and maintain long-term productivity.[3]Nutritional Profile
Macronutrients and Micronutrients
Adzuki beans (Vigna angularis) in their dry seed form offer a nutrient-dense profile, with approximately 329 kcal per 100 g serving derived primarily from complex carbohydrates and plant protein. The macronutrients include 19.87 g of protein (about 20% of the weight), 62.9 g of carbohydrates (predominantly starch), 0.53 g of fat, and 12.7 g of dietary fiber, making them a valuable source for energy and digestive health support.[6]| Macronutrient | Amount per 100 g dry | % Daily Value* |
|---|---|---|
| Calories | 329 kcal | 16% |
| Protein | 19.87 g | 40% |
| Carbohydrates | 62.9 g | 23% |
| Fat | 0.53 g | 1% |
| Fiber | 12.7 g | 45% |
| Micronutrient | Amount per 100 g dry | % Daily Value* |
|---|---|---|
| Folate | 622 µg | 155% |
| Iron | 4.98 mg | 28% |
| Potassium | 1,254 mg | 27% |
| Magnesium | 127 mg | 30% |
| Phosphorus | 381 mg | 30% |