Velvet Bean

Mucuna pruriens is a fast-growing annual climbing vine reaching several metres, with purplish flowers in long drooping clusters. Its curved pods, covered in fine, itchy hairs, hold three to seven glossy seeds that may be white, brown, grey, black or mottled. The hairs on the pods contain mucunain, which causes intense itching on contact with skin, hence the names cowhage and cowitch. The seeds have a bitter taste and a hard coat and have to be soaked and boiled thoroughly before they can be eaten. The plant is also grown widely as green manure and cover crop.

The velvet bean is believed to be native to tropical Africa and Asia, and it is now naturalised across the tropics and subtropics. It is grown or found in India, Sri Lanka, West Africa, Southeast Asia, Central America and Brazil. Its ability to fix nitrogen, smother weeds and produce large amounts of leaf biomass has made it a useful crop for restoring soil fertility in smallholder farming systems, in addition to its use for food, fodder and traditional medicine.

In India, the seeds appear in Ayurvedic texts under the name kapikacchu, and have been used in traditional preparations for many centuries. In Benin, Ghana, Nigeria and Guatemala, the roasted seeds have been used in food and as a coffee substitute, giving rise to the nickname Nescafé bean in some places. In many regions the seeds were an emergency food in times of famine, as they were available when other crops failed.

In the twentieth century, researchers discovered that the seeds contain levodopa, or L-DOPA, a precursor of dopamine, the same compound that is used as a medicine in Parkinson's disease treatment. This prompted considerable scientific interest and the sale of velvet bean powders and extracts as supplements, although quality varies and evidence is limited. Meanwhile agronomists promote the plant as a cover crop, and it is still a locally important food in several countries.

As food, the seeds must be soaked in changed water, boiled for a long time and sometimes fermented, then eaten in stews, mashed preparations or ground into flour. Roasted ground seeds are used as a coffee-like drink. In India, seed powder is taken in traditional preparations, often with milk, and extracts are sold as supplements. The leaves and young pods are cooked as vegetables in some regions, and the whole plant is used as animal feed and green manure.

Velvet bean seeds are high in protein for a legume, along with carbohydrate and fibre, and the seeds contain minerals such as iron and magnesium. Their main distinguishing feature is L-DOPA, present in amounts of a few percent by weight, depending on the variety. L-DOPA is a drug-active compound, so seeds should not be regarded as an ordinary food. Small studies of extracts have investigated their effects on movement and mood, but evidence is preliminary and not a substitute for medical care.