Cashew Tree (Anacardium occidentale)

It may surprise you to know that cashew (Anacardium occidentale) is related to poison ivy, pistachio, and even mango! It is a tropical evergreen native to Brazil and produces a wood used to build shipping crates, boats, and charcoal. The resin in the shells of the fruits are used to make insecticides and plastics, so the nuts must be separated from the shells before being sold as food. Explorers from Portugal are responsible for introducing cashews to the outside world.

I. Appearance and Characteristics

Cashew is the common name of a tropical evergreen tree Anacardium occidentale, in the family Anacardiaceae. It is native to South America and is the source of the cashew nut and the cashew apple, an accessory fruit.

The English name derives from the Portuguese name for the fruit of the cashew tree: caju (Portuguese pronunciation: ), also known as acaju, which itself is from the Tupi word acajú, literally meaning “nut that produces itself”.

The generic name Anacardium is composed of the Greek prefix ana- (ἀνά-, aná, ‘up, upward’), the Greek cardia (καρδία, kardía, ‘heart’), and the Neo-Latin suffix -ium. It possibly refers to the heart shape of the fruit, to “the top of the fruit stem” or to the seed. The word anacardium was earlier used to refer to Semecarpus anacardium (the marking nut tree) before Carl Linnaeus transferred it to the cashew; both plants are in the same family. The epithet occidentale derives from the Western (or Occidental) world.

The plant has diverse common names in various languages among its wide distribution range, including anacardier (French) with the fruit referred to as pomme de cajou, caju (Portuguese pronunciation: ), or acaju (Portuguese).

The cashew tree is large and evergreen, growing to 14 metres (46 feet) tall, with a short, often irregularly shaped trunk. The leaves are spirally arranged, leathery textured, elliptic to obovate, 4–22 centimetres (1+1⁄2–8+3⁄4 inches) long and 2–15 cm (3⁄4–6 in) broad, with smooth margins. The flowers are produced in a panicle or corymb up to 26 cm (10 in) long; each flower is small, pale green at first, then turning reddish, with five slender, acute petals 7–15 millimetres (1⁄4–5⁄8 in) long. The largest cashew tree in the world covers an area around 7,500 m2 (81,000 sq ft) and is located in Natal, 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 or red structure about 5–11 cm (2–4+1⁄4 in) long.

The true fruit of the cashew tree is a kidney-shaped or boxing glove-shaped drupe that grows at the end of the cashew apple. The drupe first develops on the tree and then the pedicel expands to become the cashew apple. The drupe becomes the true fruit, a single shell-encased seed, which is often considered a nut in the culinary sense. The seed is surrounded by a double shell that contains an allergenic phenolic resin, anacardic acid—which is a potent skin irritant chemically related to the better-known and also toxic allergenic oil urushiol, which is found in the related poison ivy and lacquer tree.

II. How to Grow and Care

Sunlight

Cashew thrives in full sunlight conditions, requiring this intensity for optimal growth and fruit production. Without adequate sun exposure, the plant’s growth can be stunted, and it might produce fewer fruits. Frequent deprive of sunlight can lead to poor plant health and increased susceptibility to pests and diseases. Cashew has a moderate tolerance to light variations, though it prefers a sunny environment. This species is characteristically adaptable, with leaves capable of orienting to maximize light absorption. It is best planted outdoors in clear, unshaded areas where it can receive at least 6-8 hours of direct sunlight daily.

Watering

Originating from the tropical climates, cashew has adapted to thrive in environments with high humidity and regular rainfall. Its water habits indicate a preference for consistent moisture without being waterlogged, showcasing moderate drought tolerance. Accordingly, it should be watered once every two weeks to maintain its hydration needs without over-saturating the soil. As an outdoor plant often found in warmer regions, cashew benefits significantly from mulching to retain soil moisture during hot periods, ensuring a stable growth cycle.

Fertilizing

For optimal health, cashew benefits from high nitrogen fertilizers, promoting robust growth and prolific fruiting. Apply a balanced N-P-K blend during active growth, reducing frequency in the dormant season. Begin with a quarterly regimen, adjusting based on plant response. Use manufacturer-recommended quantities to avoid overfertilization, which could damage cashew. Be mindful of local climate variations, with increased needs during prolonged growing seasons. To maximize uptake, apply during cool periods of the day and water thoroughly. Always wear gloves and avoid contact with cashew’s sap when fertilizing.

Propagation

Cashew can be propagated by cutting, a method that involves taking a healthy section of a stem or branch and allowing it to take root. For successful propagation, use semi-hardwood cuttings and ensure they are from disease-free mother plants. It’s important to maintain high humidity and adequate warmth to facilitate root development. Using a rooting hormone can stimulate faster root growth. Careful handling is paramount to avoid damage to the cutting, and once rooted, the young plant requires gradual acclimatization to less controlled environments.

Transplanting

Ideally, transition cashew in the heart of spring, leveraging optimal growth temperatures. Choose a sunny, sheltered spot with well-drained soil. Gently acclimate cashew to its new location to reduce transplant shock.

III. Uses and Benefits

• Nutrition

Raw cashews are 5% water, 30% carbohydrates, 44% fat, and 18% protein (table). In a 100-gram reference amount, raw cashews provide 553 kilocalories, 67% of the Daily Value (DV) in total fats, 36% DV of protein, 13% DV of dietary fiber and 11% DV of carbohydrates. Cashews are rich sources (20% or more of the DV) of dietary minerals, including particularly copper, manganese, phosphorus, and magnesium (79–110% DV), and of thiamin, vitamin B6 and vitamin K (32–37% DV). Iron, potassium, zinc, and selenium are present in significant content (14–61% DV) (table). Cashews (100 g, raw) contain 113 milligrams (1.74 gr) of beta-sitosterol.

• Nut and shell

Culinary uses for cashew seeds in snacking and cooking are similar to those for all tree seeds called nuts.

Cashews are commonly used in South Asian 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. Cashews are also used in Thai and Chinese cuisines, generally in whole form. In the Philippines, cashew is a known product of Antipolo, and is eaten with suman. The province of Pampanga also has a sweet dessert called turrones de casuy, which is cashew marzipan wrapped in white wafers. In Indonesia, roasted and salted cashews are called kacang mete or kacang mede, while the cashew apple is called jambu monyet (lit. ‘monkey rose apple’).

In the 21st century, cashew cultivation increased in several African countries to meet the demands for manufacturing cashew milk, a plant milk alternative to dairy milk. In Mozambique, bolo polana is a cake prepared using powdered cashews and mashed potatoes as the main ingredients. This dessert is common in South Africa.

• Husk

The cashew nut kernel has a slight curvature and two cotyledons, each representing around 20–25% of the weight of the nut. It is encased in a reddish-brown membrane called a husk, which accounts for approximately 5% of the total nut. Cashew nut husk is used in emerging industrial applications, such as an adsorbent, composites, biopolymers, dyes and enzyme synthesis.

• Apple

The mature cashew apple can be eaten fresh, cooked in curries, or fermented into vinegar, citric acid or 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, cashew fruit juice and the fruit pulp are used in the production of sweets, juice, mixed with alcoholic beverages such as cachaça, and as a flour, milk, or cheese. 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 being a Spanish name for cashew).

Cashew nuts are more widely traded than cashew apples, because the fruit, unlike the nut, is easily bruised and has a very limited shelf life. Cashew apple juice, however, may be used for manufacturing blended juices.

When the apple is consumed, its astringency is sometimes removed by steaming the fruit for five minutes before washing it in cold water. Steeping the fruit in boiling salt water for five minutes also reduces the astringency.

In Cambodia, where the plant is usually grown as an ornamental rather than an economic tree, the fruit is a delicacy and is eaten with salt.

• Alcohol

In the Indian state of Goa, the ripened cashew apples are mashed, and the juice, called “neero”, is extracted and kept for fermentation for a few days. This fermented juice then undergoes a double distillation process. The resulting beverage is called feni or fenny. Feni is about 40–42% alcohol (80–84 proof). The single-distilled version is called urrak, which is about 15% alcohol (30 proof). In Tanzania, the cashew apple (bibo in Swahili) is dried and reconstituted with water and fermented, then distilled to make a strong liquor called gongo.

• Nut oil

Cashew nut oil is a dark yellow oil derived from pressing the cashew nuts (typically from lower value broken chunks created accidentally during processing), and is used for cooking or as a salad dressing. The highest quality oil is produced from a single cold pressing.

• Shell oil

Cashew nutshell liquid (CNSL) or cashew shell oil (CAS registry number 8007-24-7) is a natural resin with a yellowish sheen found in the honeycomb structure of the cashew nutshell, and is a byproduct of processing cashew nuts. As it is a strong irritant, it should not be confused with the edible cashew nut oil. It is dangerous to handle in small-scale processing of the shells, but is itself a raw material with multiple uses. 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 CNSL.

– 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 lacquer and the oils of poison ivy, and they present a danger during manual cashew processing.

This natural oil phenol has interesting chemical structural features that can be modified to create a wide spectrum of biobased monomers. These capitalize on the chemically versatile construct, which contains three functional groups: the aromatic ring, the hydroxyl group, and the double bonds in the flanking alkyl chain. These include polyols, which have recently seen increased demand for their biobased 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 rigid polyurethanes, aided by their inherent phenolic structure and larger number of reactive units per unit mass.

CNSL may be used as a resin for carbon composite products. CNSL-based novolac is another versatile industrial monomer deriving from cardanol typically used as a reticulating agent (hardener) for epoxy matrices in composite applications providing good thermal and mechanical properties to the final composite material.

• Animal feed

Discarded cashew nuts unfit for human consumption, alongside the residues of oil extraction from cashew kernels, can be fed to livestock. Animals can also eat the leaves of cashew trees.

• Other uses

As well as the nut and fruit, the plant has several other uses. In Cambodia, the bark gives a yellow dye, the timber is used in boat-making, and for house-boards, and the wood makes excellent charcoal. The shells yield a black oil used as a preservative and water-proofing agent in varnishes, cements, and as a lubricant or timber seal. Timber is used to manufacture furniture, boats, packing crates, and charcoal. Its juice turns black on exposure to air, providing an indelible ink.