Kidney Bean

The kidney bean is the seed of a climbing or bush annual with trifoliate leaves and pods that hang in clusters. The mature dry seeds are about 1.5 cm long, smooth and glossy, shaped like a kidney, with colours from light pink to dark red. White kidney beans, known as cannellini, belong to the same species. The beans are firm and slightly mealy when cooked, hold their shape well in slow cooking, and absorb the flavours of sauces, which makes them suited to stews and chilli. They are sold dried, canned, or precooked in jars. Dried beans keep for a year or more if stored cool and dry, though older beans take longer to soften.

The common bean was domesticated in the Americas, with at least two separate centres: Mesoamerica, in what is now Mexico, and the southern Andes. Wild ancestors are found from northern Mexico to Argentina. The name kidney bean describes the shape of the seed. The scientific name Phaseolus comes from the Latin for a small bean or pod, and vulgaris means common. Rajma, the North Indian name, is thought to derive from a word for the bean's introduction through traders. Frijol, used in Spanish, relates to Latin words for beans.

Archaeological finds in the Andes and Mexico indicate that common beans were being cultivated several thousand years ago, often grown together with maize and squash in a system known as the three sisters. After the arrival of Europeans, beans spread to Europe, Africa and Asia within decades, and many regional landraces were developed that are now considered local classics. In Europe they largely displaced older Old World legumes such as the broad bean in some cuisines. Beans reached the Indian subcontinent in the sixteenth and seventeenth centuries, and the red kidney bean became the basis of rajma chawal, a signature dish of Punjab and Kashmir. In Mexico and the American Southwest, they are central to chilli and refried bean dishes, while in the Caribbean and Latin America red beans and rice is a beloved dish, notably in Louisiana. Kidney beans are now grown worldwide, with large producers including India, Brazil, Myanmar, China and the United States, and they have an important role as an affordable plant protein.

Kidney beans are soaked and boiled for chilli con carne, rajma curry, red beans and rice, three-bean salads, soups and minestrone. Canned beans are convenient for quick dishes and salads. They can be mashed into burgers and dips, and dried beans are ground into flour for some products. Cannellini beans are popular in Italian dishes such as pasta e fagioli. Beans can also be sprouted briefly, though safety guidance applies, and the whole plant is used as a green manure and nitrogen-fixing crop.

Kidney beans provide plant protein, soluble and insoluble fibre, folate, iron, potassium and magnesium, and they have a relatively low glycaemic index. Regular consumption of pulses is associated with improved cholesterol levels and better blood sugar control in clinical and observational research, as part of a balanced diet. The fibre feeds gut bacteria and may cause gas in some people, which usually lessens as intake becomes regular. Iron absorption from beans is lower than from meat, but it improves when eaten with vitamin C-rich foods.