The cashew tree (Anacardium occidentale) is a tropical evergreen that produces the cashew nut and the cashew apple. It can grow as high as 14 metres (46 ft), but the dwarf cashew, growing up to 6 metres (20 ft), has proved more profitable, with earlier maturity and higher yields.
The cashew nut is served as a snack or used in recipes, like other nuts, although it is actually a seed. The cashew apple is a fruit, whose pulp can be processed into a sweet, astringent fruit drink or distilled into liqueur.
The shell of the cashew nut yields derivatives that can be used in many applications from lubricants to paints, and other parts of the tree have traditionally been used for snake-bites and other folk remedies.
Originally native to northeastern Brazil, the tree is now widely grown in tropical regions, India and Nigeria being major producers, in addition to Vietnam, the Ivory Coast, and Indonesia.
Its English name derives from the Portuguese for the fruit of the cashew tree, caju (Portuguese pronunciation: which itself is derived from the indigenous Tupi name, acajú. The name Anacardium, originally from the Greek, actually refers to the nut, core or heart of the fruit, which is outwardly located (ana means “upwards” and -cardium means “heart”). In the Tupian languages, acajú means “nut that produces itself.”
Habitat and growth
The cashew tree is large and evergreen, growing to 10-12m (~32 ft) tall, with a short, often irregularly shaped trunk. The leaves are spirally arranged, leathery textured, elliptic to obovate, 4 to 22 cm long and 2 to 15 cm broad, with smooth margins. The flowers are produced in a panicle or corymb up to 26 cm long; each flower is small, pale green at first, then turning reddish, with five slender, acute petals 7 to 15 mm long. The largest cashew tree in the world covers an area of about 7,500 square metres (81,000 sq ft); it is located in Natal, Rio Grande do Norte, Brazil.
The fruit of the cashew tree is an accessory fruit (sometimes called a pseudocarp or false fruit). What appears to be the fruit is an oval or pear-shaped structure, a hypocarpium, that develops from the pedicel and the receptacle of the cashew flower. Called the cashew apple, better known in Central America as marañón, it ripens into a yellow and/or red structure about 5–11 cm long. It is edible, and has a strong “sweet” smell and a sweet taste. The pulp of the cashew apple is very juicy, but the skin is fragile, making it unsuitable for transport. In Latin America, a fruit drink is made from the cashew apple pulp which has a very refreshing taste and tropical flavor that can be described as having notes of mango, raw green pepper, and just a little hint of grapefruit-like citrus.
The true fruit of the cashew tree is a kidney or boxing-glove shaped drupe that grows at the end of the cashew apple. The drupe develops first on the tree, and then the pedicel expands to become the cashew apple. Within the true fruit is a single seed, the cashew nut. Although a nut in the culinary sense, in the botanical sense the nut of the cashew is a seed. The seed is surrounded by a double shell containing an allergenic phenolic resin, anacardic acid, a potent skin irritant chemically related to the better-known allergenic oil urushiol which is also a toxin found in the related poison ivy. Properly roasting cashews destroys the toxin, but it must be done outdoors as the smoke (not unlike that from burning poison ivy) contains urushiol droplets which can cause severe, sometimes life-threatening, reactions by irritating the lungs. People who are allergic to cashew urushiols may also react to mango or pistachio which are also in the Anacardiaceae family. Some people are allergic to cashew nuts, but cashews are a less frequent allergen than other nuts or peanuts.
While the cashew plant is native to northeast Brazil, the Portuguese took it to Goa, India, between 1560 and 1565. From there it spread throughout Southeast Asia and eventually Africa.
Cashew nuts are a popular snack and food source. Cashews, unlike other oily tree nuts, contain starch to about 10% of their weight. This makes them more effective than other nuts in thickening water-based dishes such as soups, meat stews, and some Indian milk-based desserts. Many southeast Asian cuisines use cashews for this unusual characteristic, rather than other nuts.
The shell of the cashew nut is toxic, which is why the shell is removed before it is sold to consumers.
Cashew nuts are commonly used in Indian cuisine, whole for garnishing sweets or curries, or ground into a paste that forms a base of sauces for curries (e.g., korma), or some sweets (e.g., kaju barfi). It is also used in powdered form in the preparation of several Indian sweets and desserts. In Goan cuisine, both roasted and raw kernels are used whole for making curries and sweets.
The cashew nut can also be harvested in its tender form, when the shell has not hardened and is green in color. The shell is soft and can be cut with a knife and the kernel extracted, but it is still corrosive at this stage, so gloves are required. The kernel can be soaked in turmeric water to get rid of the corrosive material before use. Cashew nuts are also used in Thai and Chinese cuisine, generally in whole form.
In the Philippines, cashew is a known product of Antipolo, and is eaten with suman. Pampanga also has a sweet dessert called turrones de casuy, which is cashew marzipan wrapped in white wafers.
In Indonesia, roasted and salted cashew nut is called kacang mete or kacang mede, while the cashew apple is called jambu monyet (literally means monkey rose apple).
In Mozambique, bolo polana is a cake prepared using powdered cashews and mashed potatoes as the main ingredients. This dessert is popular in South Africa, too.
South American countries have developed their own specialities. In Brazil, the cashew fruit juice is popular all across the country. In Panama, the cashew fruit is cooked with water and sugar for a prolonged time to make a sweet, brown, paste-like dessert called dulce de marañón. Marañón is one of the Spanish names for cashew.
Nigeria was the world’s largest producer of cashew nuts with shell in 2010. Cashew nut production trends have varied over the decades. African countries used to be the major producers before the 1980s; India became the largest producer in the 1990s, followed by Vietnam which became the largest producer in the mid-2000s. In 2008, Nigeria has become the largest producer. As of 2014 though, the rapid growth of the culture in Côte d’Ivoire made this country the first African producer, first global exporter and second world producer after India. Cashew nuts are produced in tropical countries because the tree is very frost sensitive; they have been adapted to various climatic regions around the world between the latitudes of 25°N and 25°S.
Peru reported the world’s highest production yields for cashew nuts in 2010, at 5.27 metric tons per hectare, nearly nine times the world average. The traditional cashew tree is tall (up to 14 m) and takes three years from planting before it starts production, and eight years before economic harvests can begin. More recent breeds, such as the dwarf cashew trees, are up to 6 m tall, and start producing after the first year, with economic yields after three years. The cashew nut yields for the traditional tree are about 0.25 metric tons per hectare, in contrast to over a ton per hectare for the dwarf variety. Grafting and other modern tree management technologies are used to further improve and sustain cashew nut yields in commercial orchards.
Fluctuations in world market prices for cashew nuts have been a source of discontent for communities in Tanzania which grow the nut as a cash crop; reduced payments in April 2013 sparked serious rioting in Liwale District in the south of the country.
The fats and oils in cashew nuts are 62% monounsaturated fat, 18% polyunsaturated fat, and 21% saturated fat (9% palmitic acid (16:0) and 7% stearic acid (18:0))
Cashews, as with other tree nuts, are a good source of antioxidants. Alkyl phenols, in particular, are abundant in cashews. Cashews are also a source of dietary trace minerals copper, manganese, magnesium and phosphorus.
For some people, cashews, like other tree nuts, can lead to complications or allergic reactions. Cashews contain gastric and intestinal soluble oxalates, albeit less than some other tree nuts; people with a tendency to form kidney stones may need moderation and medical guidance. Allergies to tree nuts such as cashews can be of severe nature to some people. These allergic reactions can be life-threatening or even fatal; prompt medical attention is necessary if tree nut allergy reaction is observed. These allergies are triggered by the proteins found in tree nuts, and cooking often does not remove or change these proteins. Reactions to cashew and other tree nuts can also occur as a consequence of hidden nut ingredients or traces of nuts that may inadvertently be introduced during food processing, handling or manufacturing. Many nations require food label warning if the food may get inadvertent exposure to tree nuts such as cashews. Individuals with IgE-mediated allergy to cashews are highly likely to be sensitized to the botanically related pistachio nut.
In some people, cashew nut allergy may be a different form, namely birch pollen allergy. This is usually a minor form. Symptoms are confined largely to the mouth.
Cashew oil is a dark yellow oil for cooking or salad dressing pressed from cashew nuts (typically broken chunks created during processing). This may be produced from a single cold pressing.
Cashew shell oil
Cashew nutshell liquid (CNSL) or cashew shell oil (CAS registry number 8007-24-7) is a natural resin found in the honeycomb structure of the cashew nutshell and is a byproduct of processing cashew nuts. It is a raw material of multiple uses in developing drugs, antioxidants, fungicides, etc. It is used in tropical folk medicine and for anti-termite treatment of timber. Its composition varies depending on how it is processed.
Cold, solvent extracted CNSL is mostly composed of anacardic acids (70%), cardol (18%) and cardanol (5%).
Heating CNSL decarboxylates the anacardic acids, producing a technical grade of CNSL that is rich in cardanol. Distillation of this material gives distilled, technical CNSL containing 78% cardanol and 8% cardol (cardol has one more hydroxyl group than cardanol). This process also reduces the degree of thermal polymerization of the unsaturated alkyl-phenols present in cashew shell nut liquid.
Anacardic acid is also used in the chemical industry for the production of cardanol, which is used for resins, coatings, and frictional materials.
These substances are skin allergens, like the oils of the poison ivy, and present danger during manual cashew processing.
This natural oil phenol has been found to have interesting chemical structural features which enable a range of chemical modifications to create a wide spectrum of bio-based monomers capitalizing on the chemically versatile construct, containing three different functional groups, the aromatic ring, the hydroxyl group and the double bonds in the flanking alkyl chain. These can be split into key groups, used as polyols, which have recently seen a dramatic increase in demand for their bio-based origin and key chemical attributes such as high reactivity, range of functionalities, reduction in blowing agents and naturally occurring fire retardant properties in the field of ridged polyurethanes aided by their inherent phenolic structure and larger number of reactive units per unit mass.
CNSL based Novolac is another versatile industrial monomer deriving from cardanol typically used as a reticulating agent for epoxy matrices in composite applications providing good thermal and mechanical properties to the final composite material.
Further examples of applications which are cashew shell nut liquid derived materials are being evaluated, are in the fields of chemical intermediates, additives, stabilizers, lubricants, diesel engine fuel alternatives, poor point dispersants, anti-oxidants, and anticorrosive paints.
Abrasives and friction dusts have also been developed from Residol, the residue byproduct of this synthesis process.
Other uses of cashew shell oil have been explored, including as an additive to brake fluid, to reduce brake fade and brake lining wear.
Composite Technical Services (Kettering, Ohio, USA) has researched the use of cashew shell oil (which has a yellowish sheen) as a resin for carbon composite products.
The cashew apple, also called cashew fruit, is the fleshy part of the cashew fruit that is attached to the cashew nut. The top end of the cashew apple is attached to the stem that comes off the tree. The bottom end of the cashew apple attaches to the cashew nut, which is encased in a shell. In botanical terms, the cashew apple is an accessory fruit that grows on the cashew seed (which is the nut).
The cashew apple is a soft fruit, rich in nutrients, and contains five times more vitamin C than an orange. It is eaten fresh, cooked in curries, or fermented into vinegar, as well as an alcoholic drink. It is also used to make preserves, chutneys, and jams in some countries such as India and Brazil. In many countries, particularly in South America, the cashew apple is used to flavor drinks, both alcoholic and nonalcoholic. In Brazil, it is a popular fruit flavor for the national drink, the caipirinha.
In much of Brazil, people regard the cashew apple as the delicacy, rather than the nut kernel which is popular elsewhere. In fact, in parts of Brazil and neighbour countries, the cashew apple is more popular as a food than is the cashew nut. A large reason for this is simply the availability of cashew apples. They tend to be popular where they are readily available.
Cashew nuts are more popular than cashew apples in many parts of the world—regions that do not grow cashews—because the fruit, unlike the nut, is difficult to transport to these places. Unlike cashew nuts, cashew apples are extremely soft and easily bruised in shipment. For this reason, cashew juice and cashew juice concentrate are often shipped to these nonlocal countries instead of the fresh fruit.
Cashew apples have a sweet but astringent taste. This astringency has been traced to the waxy layer on the skin that contains a chemical, urushiol, which can cause minor skin irritation to areas that have had contact with it. It is almost identical to the astringency caused by the skin of a mango, which also contains urushiol. The astringency from mango skin can be mildly tasted in the flesh of mango fruit, just as the astringency of cashew apple skin can be mildly tasted in the flesh of cashew apples. In cultures that consume cashew apples, this astringency is sometimes removed by steaming the fruit for five minutes before washing it in cold water; alternatively, boiling the fruit in salt water for five minutes or soaking it in gelatin solution also reduces the astringency. When mixed in drinks or used as a flavoring, the astringency becomes highly diluted and typically causes no irritation to those without urushiol allergies.
Young cashew nuts
In Goa, the cashew apple (the accessory fruit) is mashed, the juice is extracted and kept for fermentation for a few days. Fermented juice then undergoes a double distillation process. The resulting beverage is called feni or fenny. Feni is about 40-42% alcohol. The single-distilled version is called urrac, which is about 15% alcohol.
In the southern region of Mtwara, Tanzania, the cashew apple (bibo in Swahili) is dried and saved. Later it is reconstituted with water and fermented, then distilled to make a strong liquor often referred to by the generic name, gongo.
In Mozambique, cashew farmers commonly make a strong liquor from the cashew apple, agua ardente (burning water).
According to An Account of the Island of Ceylon by Robert Percival an alcohol had been distilled in the early 20th century from the juice of the fruit, and had been manufactured in the West Indies. Apparently, the Dutch considered it superior to brandy as a liqueur.
Many parts of the plant are used in the traditional medicine of the Patamona of Guyana. They grind the seeds into a poultice for treating snakebites, apply nut oil to cracked heels or as an antifungal agent, and use the fruits, bark, and leaves for many other purposes including anti-fungal activity, for sores and rashes, or as an antipyretic, and for antidiarrheal applications. The leaf extracts with petroleum ether and ethanol inhibited growth of several species of bacteria and fungi. Chemicals identified in cashew shell oil have been assayed against Streptococcus mutans, a bacterium responsible for many dental cavities, and found to have activity in vitro against this and other Gram positive bacteria.