The characteristically curved, edible seed or nut of the domesticated cashew tree. The tropical and subtropical evergreen shrub or tree is native to the New World, but commercially cultivated mainly in Brazil and India. The nut, rich in oil and distinctively flavoured, is a commonly used ingredient in South and Southeast Asian cuisine, and it is a characteristic ingredient of numerous chicken and vegetarian dishes of southern India. In Western countries it is eaten mainly as a premium-quality snack food.
The cashew tree produces wood that is useful in local economies for such practical items as shipping crates, boats, and charcoal (and also for a gum that it produces that is similar to gum arabic), but most cultivation is directed toward production of the valuable nut crop.
The plant may grow to 12 metres (40 feet) in height where the soil is fertile and the humidity high. The nut, shaped like a large, thick bean, is sometimes more than 2.5 cm (1 inch) long and forms in an unusual way. It appears as though one of its ends had been forcibly sunk into the end of a pear-shaped, swollen stem, called the cashew apple, which is about three times as large as the nut and reddish or yellow. The cashew apple is used locally in beverages, jams, and jellies. The nut has two walls, or shells; the outer, smooth and glasslike, over the surface, thin and somewhat elastic but stout, and olive green until maturity, when it becomes strawberry roan. The inner shell is harder and must be cracked like the shells of other nuts to obtain the edible portion inside. A brown oil between the shells blisters human skin and is used as a lubricant and an insecticide and in the production of plastics.
The fruits are picked by hand, and the nuts are first detached, then sun dried. In some localities the dried nuts are roasted amid burning logs, where the heat causes the outer shells to burst open and release the oil. The oil quickly catches fire, giving off fumes injurious to the eyes and skin. In improved methods of roasting, the poisonous properties are dispelled in roasting cylinders. Later, the inner shells are broken open by hand and the kernels heated to remove the skins.
The cashew is probably native to northeastern Brazil. Portuguese missionaries took it to East Africa and India during the late 16th century, where it became abundant at low altitudes near the seacoast. Parts of the cashew must be handled with care by susceptible individuals; it is related to the American poison ivy and poison sumac. The wild cashew, or espave (A. excelsum), is a closely related tree that grows in Central and South America. Both species are members of the sumac family.