A small to medium tree, generally single-trunked and
spreading in habit, up to 40' in height but generally 10-20' in
cultivation. In older trees, spread may be greater than
height, with lower limbs bending to touch the ground. Leaves are thick,
prominently veined, oval to spatulate in shape, with blunt tips and
entire margins. New foliage contains reddish pigment
CURRENT PRACTICAL USES Specific indications and Uses.Post-partum and
other uterine hemorrhage, with profuse flow, cold extremities,
and pallid surface; haematuria; haemoptysis.
Common names: Cashew,
Parts Used: Seeds, Leaves, Bark
Fruit juice: daily
caustic shell oil: externally
Cashew is native to northeastern Brazil, in the area between the Atlantic rain forest and the Amazon rainforest. The vegetation type of the region is dry forest, savannah woodland or thorn scrub, and includes the almost desert-like Caatinga. Cashew is sometimes referred to as a rainforest species and the nuts are found in products that have a rainforest friendly label or connotation. Although the trees will grow in tropical wet forests, they rarely produce many nuts, and production is far greater in areas with a distinct wet and dry season, such as its native range in Brazil, India and east Africa.
The Portuguese introduced cashew to the west coast of India and east Africa in the 16th century, shortly after its discovery in 1578. It was planted in India initially to reduce erosion, and uses for the nut and pseudofruit, the cashew apple, were developed much later. The trees were well adapted to the region, and became naturalized. Trees also became naturalized in Central America and the Caribbean islands. Nut domestication predated the arrival of Europeans to Brazil, although international nut trade did not occur until the 1920s. Native South Americans discovered that roasting nuts in fire would remove the caustic oil, allowing the nut to be cracked and consumed without any ill effects. The roasting practice was either not known or not appreciated outside the native range, and as a result the cashew apple was the first product consumed, with the nut being discarded. Natives also knew of many medicinal uses for the apple juice, bark, and caustic seed oil that were later exploited by Europeans.
India developed more refined methods for removing the caustic shell oil, and this country is given credit for developing the modern nut industry. India led the world in cashew production for many years until just recently, when production in Viet Nam surged about 3-fold in a few years. In its native Brazil, cashew nut production ranks in the top 5 of the world, and virtually all cashew apples and juice products come from this country. Preliminary data indicate the cashew nut production surpassed almond in 2003, and thus cashew now claims the title of #1 nut crop in the world.
Medicinal uses of cashew bark, leaves, and apple juice are plentiful, and were well known prior to recorded history in the native region of Brazil. Bark teas were used for diarrhea, and the caustic shell oil was used to treat skin infections, warts, worms, and botfly larvae beneath the skin. Teas and fruit juices are known to have antimicrobial, anti-inflammatory, astringent, diuretic, hypoglycemic, and other medicinal properties. The active principles are thought to be tannins, anacardic acid, and cardol. The red apples have higher tannin content than the yellow. Modern uses of shell oil and fruit juice include facial peels and scalp conditioners and shampoos. Clinical studies have documented the anti-inflammatory properties of tannins, and the antimicrobial properties of anacardic acid against several species, including Escherichia coli and Helicobacter pylori. Leaf extracts show hypoglycemic activity in rodents, and a reduction in artificially induced diabetes. Cashew apples contain up to 5 times the amount of vitamin C as citrus and strawberries, and higher amounts of some minerals than other fruits.
Cashew nut shell liquid (CNSL) is sandwiched in a honeycomb layer of tissue between the two walls of the nut shell. Industrial uses include automobile brakes, adhesives, paints and varnishes, insecticides, electrical insulation, and anti-microbials. The shell oil is highly caustic, causing moderate to severe skin irritation. When wood is burned or nuts roasted, contact with or breathing of the fumes can cause skin and eye irritation, inflammation, and poisoning. In addition to CNSL, resins and gums from fruit stems or bark is used as a varnish for books, wood, and flooring to protect from ants and other home-invading insects.
The nut shell has an inner and outer wall, separated by a honeycomb tissue infused with caustic oil. Cracking the nuts fresh results in the oil contaminating the kernel, so nuts are roasted to drive off oils before they are shelled. The nuts are about 22-30% kernel by weight, and kernels are difficult to extract whole compared to other tree nuts.
Soils and Climate
Cashews are said to be tolerant of sandy, poor soils where many other crops will not thrive. Soil pH is generally on the acidic side, 4.5-6.5. Trees are strongly taprooted and drought tolerant if soils are deep, and can grow in areas receiving only 30-50" of rain per year. Cashews are especially intolerant of poor soil drainage.
Climatically, cashews prefer hot, tropical lowlands (< 3000 ft elevation) with a distinct dry season. High rainfall and humidity favor diseases that destroy the flowers and reduce fruit set. They have no cold tolerance whatsoever, requiring protection from cold even in extreme southern Florida.
Propagation is most often by seed, planted directly in the field where the tree is to be sited. Improved cashews are propagated by grafting, layering, or cuttings. Fruit production occurs in 4-5 yr from seed, and 2-3 yr from vegetative propagation.
Rootstocks - generally none, but cashew seedlings can be used for rootstocks for grafted trees.
Planting Design, Training, Pruning
Cashews are planted at various densities, depending on the intensity of production, amount of rainfall, and other factors. New plantings are often established with 20-35 ft between trees and rows. Higher densities are possible, but require selective tree thinning as canopies enlarge. In arid Tanzania, research showed that when about 50-60% of the ground area was covered by cashew tree canopy, yield per acre was maximized. This is a relatively low amount of light interception compared to intensive orchards, and probably reflects the need for trees to explore large soil volumes in arid areas.
Cashews form open, spreading canopies naturally, and very little information on pruning exists.
The cashew apple and nut abscise from trees naturally when ripe. Maturation occurs over a period of several weeks during the dry season.
Nuts are collected from the ground by hand. Frequent passes though the planting must be made if apples are to be utilized, as they are highly perishable. Rain at harvest may increase rot and stimulate nut germination.
The presence of caustic cashew nut shell liquid (CNSL) in the shells makes cashew processing more difficult and hazardous than for other nut crops. After harvest, the nuts are dried in the sun or in simple tray driers and stored for processing later. Dried nuts can be stored for about 2 years at room temperature after reaching water contents of 5-10%. Nuts are re-hydrated partially by soaking or storing in high humidity since this facilitates extraction of whole kernels and CNSL. Nuts are separated by size before roasting to ensure uniformity of the roasting process.
Nuts are roasted in one of two ways: heating in pans or drums over fire, or in hot oil. Heating in pans is done in small scale operations. About 2 pounds of nuts are placed in a shallow, broad pan much like a wok, which is heated over a fire. The CNSL exuded from the shells ignites, and the nuts are stirred while they flame and smoke for about 2 minutes. The smoke and flame is dowsed with water, and nuts removed from the pan to dry. Drum roasters are semi-mechanized forms of pan roasting, where nuts are fed into the high end of a large metal, rotating drum that is tilted from horizontal. The nuts catch fire during their transit along the drum and are sprayed with water at the low end where they exit the drum. The hot oil methods are the most sophisticated and generally reserved for larger processing facilities. Nuts are immersed in a tank of CNSL heated to 375°F, and CNSL is driven out of the shell, increasing the volume of hot oil in the tank. About 50% of the oil is removed in 1-4 minutes, which is enough to allow safe cracking of nuts. Roasting in hot oil is the only method that captures CNSL as a by-product of cashew production.
After roasting, nuts are shelled either by hand or in machines. Hand shelling uses wooden mallets to crack nuts, which is very slow and tedious (only a few nuts per minute). However, cracking employs a large number of people in poor, rural areas where cashews are grown. Machine cracking can increase efficiency to a few dozen to 1000 kg of nuts per hour, but is used in only sophisticated operations. Machines either use knives to open shells, or centrifugal force to throw nuts against a hard surface. Hand cracking yields high numbers of whole kernels, but whole kernel yields from machines vary from 20-75%. Kernels are then dried in the sun or ovens at 160°F until the moisture content is about 3%. The papery seed coat must be removed from the nut, usually by hand at rates of up to about 25 lbs per day. Nuts are graded by hand, and separated into whole kernels and various sized pieces of broken kernels. Nuts are vacuum packed or packed in carbon dioxide for export.
Cashew apples can be juiced easily since they do not contain seed, however, juicing must be done immediately at harvest. Apples yield about 60-70% of their weight as juice. Poor flavors, due to tannins and oils, can be removed by steam treatment, cooking in brine, or adding gelatin to juice with subsequent filtration (tannins are precipitated by gelatin, as in wine). Juice can be concentrated and frozen, or sulfited and stored at room temperature for several weeks. Juice has properties allowing it to be fermented to wine easily; Feni is a distilled beverage of about 40% alcohol content made from cashew wine distillation.
Vacuum packed, roasted nuts can be stored for up to one year, and carbon dioxide packing extends life an additional year.
The cashew apple may be consumed fresh, but contains high quantities of tannins yielding a bitter taste and dry mouth feel. It is more often cooked, partially dried, or candied, as in the Dominican Republic and India. The alcoholic drink, Feni, is made from fermented cashew apple juice in India. The wine made from the juice is said to be the finest made from tropical fruits.
Per capita consumption of cashew is unknown, but that of all tree nuts is 2.7 lbs/year in the USA. Cashews are likely to be less than 1 lb/year.
Dietary value, per 100 gram edible portion
Crude Fiber (%)
% of US RDA*
A small to medium tree, generally single-trunked and spreading in habit, up to 40' in height but generally 10-20' in cultivation. In older trees, spread may be greater than height, with lower limbs bending to touch the ground. Leaves are thick, prominently veined, oval to spatulate in shape, with blunt tips and entire margins. New foliage contains reddish pigment
CURRENT PRACTICAL USESEvery part of the cashew tree can be used: the root is a cleanser (purgative) while the light, water resistant bark is used to make canoes; the antibiotic property of the fruit juice, which is also rich in vitamin C, cures symptoms of the common cold, sore throat, flu and dysentery; the fruit itself treats premature aging of the skin and the nut alleviates cough, hiccup, depression and lowers blood cholesterol; the gum from the fruit stems is a natural repellent against insects and ants while the oil in the shell of the nut is used commercially for varnish, paints, shampoos and conditioners. Furthermore the medicinal properties of cashew have been evident against diabetes, tumors, and kidney problems.
Specific indications and Uses.Post-partum and other uterine hemorrhage, with profuse flow, cold extremities, and pallid surface; haematuria; haemoptysis.