Winged Bean

Psophocarpus tetragonolobus is a perennial vine, usually grown as an annual, that climbs several metres on supports. Its distinctive pods are 6 to 36 centimetres long with four frilly wings running down their length, giving them a square cross-section when cut. The immature pods are eaten like green beans, with a crisp, mild flavour. Mature pods contain 5 to 20 round seeds that are brown, cream or black. The plant also forms starchy, tuberous roots, and the flowers, which are pale blue, and the young leaves are eaten as vegetables.

The winged bean's origin is uncertain. It is generally believed to come from tropical Asia, with Papua New Guinea and Indonesia often suggested, though some researchers have also argued for Africa. It has been grown for a long time in Papua New Guinea, Myanmar, Thailand, Indonesia, the Philippines and southern India and Sri Lanka, and has been introduced to West Africa and the Caribbean. It thrives in hot, humid conditions and is sensitive to day length, which has limited its use in temperate zones.

For a long time, winged bean was a regional garden crop in Southeast Asia and Melanesia, known to local farmers but little recognised elsewhere. Its potential as a food was highlighted in 1975, when the United States National Academy of Sciences published a report, The Winged Bean: A High-Protein Crop for the Tropics, which described it as a promising plant for improving diets in developing countries.

The report stimulated research projects in several countries, which found that the plant could produce high-protein seeds, edible tubers and nutritious leaves. Problems with uneven yields, pod shattering, long maturation and the need for staking, as well as the cost of processing the seeds, limited its spread as a major crop. It has remained a valued local vegetable and an object of scientific interest, and breeding programmes continue.

The young pods are eaten sliced raw in salads, stir-fried, curried or pickled, especially in Thai, Indonesian, Malaysian and Sri Lankan cuisines. Mature seeds are boiled thoroughly or processed into flour, tempeh-like fermented food, milk or oil, similar to soy. Young leaves are cooked as greens and flowers added to salads. The tubers are boiled or roasted. The plant is also used as a green manure and cover crop.

Dry winged bean seeds are very high in protein and contain notable amounts of fat, similar to soybeans, along with fibre and minerals. The leaves and young pods provide vitamins, including vitamin C and provitamin A, in fresh form. Tubers are a starchy, protein-richer root than cassava. The seeds do contain antinutritional factors, including trypsin inhibitors and lectins, which cooking reduces. Nutrient levels vary between varieties.