Thepeanut (Arachis hypogaea), also known as thegroundnut,[a][2]goober (US),[3]goober pea,[4]pindar (US)[3] ormonkey nut (UK), is alegume crop grown mainly for its edibleseeds, contained in underground pods. It is widely grown in thetropics andsubtropics by small and large commercial producers, both as agrain legume[5] and as an oil crop.[6]Underground fruiting (geocarpy) is atypical among legumes, which led botanistCarl Linnaeus to name the specieshypogaea, from Greek 'under the earth'.[7]
Edible products includepeanut oil andpeanut butter. Industrial uses include paint, varnish, and furniture polish made with peanut oil. The plant tops are used forsilage, while oilcake meal is used as animal feed and as a fertilizer. Peanut sauces are used in Latin America and Southeast Asia, while in the Indian subcontinent, they are added to salads and stews. In North America, peanuts are used in candies, cakes, and cookies, while peanut butter is widely eaten.
The leaves areopposite andpinnate with four leaflets (two opposite pairs; no terminal leaflet); each leaflet is 1 to 7 cm (1⁄2 to2+3⁄4 in) long and1 to 3 cm (1⁄2 to1+1⁄4 in) across. Like those of many other legumes, the leaves arenyctinastic; that is, they have "sleep" movements, closing at night.[11] The flowers are1 to 1.5 cm (3⁄8 to5⁄8 in) across, and yellowish orange with reddish veining.[12][9] They are borne inaxillary clusters on the stems.[8]
Peanut fruits develop underground, an unusual feature known asgeocarpy.[13] Afterfertilization, a short stalk at the base of the ovary—often termed agynophore, but which appears to be part of the ovary—elongates to form a thread-like structure known as a "peg". This peg grows into the soil, allowing the fruit to develop underground.[13] These pods, technically called legumes, are 3 to 7 centimetres (1 to 3 in) long, normally containing one to fourseeds.[12][9] The shell of the peanut fruit consists primarily of a mesocarp with several large veins traversing its length.[13] Botanically they arenot nuts ("fruit whoseovary wall becomes hard at maturity").[14]
Illustration of a peanut plant and pods with seeds inLes plantes potagères,Vilmorin-Andrieux, 1903
TheArachis genus is native toSouth America, east of theAndes, around Peru, Bolivia, Argentina, and Brazil.[17] Cultivated peanuts (A. hypogaea) arose from ahybrid between two wild species of peanut, thought to beA. duranensis andA. ipaensis.[17][18][19] The initial hybrid would have been sterile, but spontaneouschromosome doubling restored its fertility, forming what is termed anamphidiploid orallotetraploid.[17] Genetic analysis suggests the hybridization may have occurred only once and gave rise toA. monticola, a wild form of peanut that occurs in a few limited locations in northwestern Argentina, or in southeastern Bolivia, where the peanutlandraces with the most wild-like features are grown today,[12] and byartificial selection toA. hypogaea.[17][18]
The process of domestication through artificial selection madeA. hypogaea dramatically different from its wild relatives. The domesticated plants are bushier, more compact, and have a different pod structure and larger seeds. From thiscenter of origin, cultivation spread and formed secondary and tertiarycenters of diversity in Peru, Ecuador, Brazil, Paraguay, and Uruguay. Over time, thousands of peanut landraces evolved; these are classified into six botanical varieties and two subspecies (as listed in the peanut scientific classification table). SubspeciesA. h. fastigiata types are more upright in their growth habit and have shorter crop cycles. SubspeciesA. h. hypogaea types spread more on the ground and have longer crop cycles.[12]
The oldest knownarcheological remains of pods have been dated at about 7,600 years old, possibly a wild species that was in cultivation, orA. hypogaea in the early phase of domestication.[20] They were found in Peru, where dry climatic conditions are favorable for the preservation of organic material. Almost certainly, peanut cultivation predated this at the center of origin where the climate is moister. Manypre-Columbian cultures, such as theMoche, depicted peanuts in their art.[21] Cultivation was well-established inMesoamerica before the Spanish arrived. There, theconquistadors found thetlālcacahuatl (the plant'sNahuatl name, hence the name inSpanishcacahuate) offered for sale in the marketplace ofTenochtitlan. Its cultivation was introduced in Europe in the 19th century through Spain, particularlyValencia, where it is still produced, albeit marginally.[22] European traders later spread the peanut worldwide, and cultivation is now widespread in tropical and subtropical regions. InWest Africa, it substantially replaced a crop plant from the same family, theBambara groundnut, whose seed pods also develop underground.[23]
Peanuts were introduced to the U.S. during thecolonial period and grown as a garden crop.[24][9] Starting in 1870, they were used as ananimal feedstock until human consumption grew in the 1930s.[9]George Washington Carver (1864–1943) championed the peanut as part of his efforts for agricultural extension in the American South, where soils were depleted after repeated plantings of cotton. He invented and promulgated hundreds of peanut-based products, including cosmetics, paints, plastics, gasoline and nitroglycerin.[25]
Peanut butter was first manufactured in Canada by a process patented in the U.S. in 1884 byMarcellus Gilmore Edson ofMontreal.[26] Peanuts were sold in North America at fairs or by pushcart operators throughout the 19th century.[27] Peanut butter became well known in the United States after theBeech-Nut company began selling it at theSt. Louis World's Fair in 1904.[28] TheU.S. Department of Agriculture initiated a program to encourage agricultural production and human consumption of peanuts in the late 19th and early 20th centuries.[9]
Cultivation
Agronomy
World distribution map. Areas are political and may exceed the actual area under cultivation. Key: Green=Natural range; Purple=Introduced.[8]
Peanuts grow best in light, sandyloam soil with a pH of 5.9–7. Their capacity to fix nitrogen means that providing they nodulate properly, peanuts benefit little or not at all from nitrogen-containingfertilizer,[29] and they improvesoil fertility. Therefore, they are valuable incrop rotations. Also, the yield of the peanut crop itself is increased in rotations through reduced diseases, pests, and weeds. For example, inTexas, peanuts in a three-year rotation with corn yield 50% more than non-rotated peanuts.[29] Adequate levels of phosphorus, potassium, calcium, magnesium, and micronutrients are also necessary for good yields.[29] Peanuts need warm weather throughout the growing season to develop well. They can be grown with as little as 350 mm (14 in) of water,[30] but for best yields need at least 500 mm (20 in).[31] Depending on growing conditions and the cultivar of peanut, harvest is usually 90 to 130 days after planting for subspeciesA. h. fastigiata types, and 120 to 150 days after planting for subspeciesA. h. hypogaea types.[30][32][33]
Peanut plants continue to produce flowers when pods are developing; therefore, some pods are immature even when they are ready for harvest. To maximize yield, the timing of harvest is important. If it is too early, too many pods will be unripe; if too late, the pods will snap off at the stalk and remain in the soil.[34] For harvesting, the entire plant, including most of the roots, is removed from the soil.[34]
The main yield-limiting factors in semi-arid regions are drought and high-temperature stress. The stages of reproductive development before flowering, at flowering, and at early pod development are particularly sensitive to these constraints. Apart fromnitrogen,phosphorus andpotassium, other nutrient deficiencies causing significant yield losses arecalcium,iron andboron. Biotic stresses mainly include pests, diseases, and weeds. Among insects pests, pod borers, aphids, and mites are of importance. The most important diseases are leaf spots, rusts, and the toxin-producing fungusAspergillus.[35]
In mechanized systems, a machine is used to cut off the main root of the peanut plant by cutting through the soil just below the level of the peanut pods. The machine lifts the "bush" from the ground, shakes it, then inverts it, leaving the plant upside down to keep the peanuts out of the soil. This allows the peanuts to dry slowly to a little less than a third of their original moisture level over three to four days. Traditionally, peanuts were pulled and inverted by hand. After the peanuts have dried sufficiently, they arethreshed, removing the peanut pods from the rest of the bush.[34]
Cultivation
Pegs growing into the soil. The buried tip of the peg develops into a fruit.
There are many peanutcultivars grown around the world. The market classes grown in the United States are Spanish, Runner, Virginia, and Valencia.[36] Peanuts are produced in three major areas of the U.S.: the southeastern region which includes Alabama, Georgia, and Florida; the southwestern region which includesNew Mexico,Oklahoma, and Texas; and in the general eastern U.S. which includes Virginia, North Carolina, and South Carolina.[36] In Georgia,Naomi Chapman Woodroof is responsible for developing the breeding program of peanuts, resulting in a harvest almost five times greater.[37]
The small Spanish types are grown in South Africa and the southwestern and southeastern United States. Until 1940, 90% of the peanuts grown in theU.S. state of Georgia were Spanish types, but the trend since then has been larger-seeded, higher-yielding, moredisease-resistant cultivars. Spanish peanuts have a higher oil content than other types of peanuts. In the U.S., the Spanish group is primarily grown in New Mexico, Oklahoma, and Texas.[36]
Pests and diseases
If peanut plants are subjected to severe drought during pod formation, or if pods are not properly stored, they may become contaminated with the moldAspergillus flavus which may producecarcinogenicaflatoxins. Lower-quality and moldy peanuts are more likely to be contaminated.[38] The USDA tests every truckload of raw peanuts for aflatoxin; any containing more than 15 parts per billion are destroyed. The industry has manufacturing steps to ensure all peanuts are inspected for aflatoxin.[39] Peanuts tested to have high aflatoxin are used to make peanut oil where the mold can be removed.[40] The ant leaves can be affected by a fungus,Alternaria arachidis.[41]
In 2023, world production of peanuts (reported as groundnuts excluding shelled) was 54 milliontonnes, led by China with 36% of the total and India with 19% (table).
Some people (1.4–2% in Europe and the United States) experienceallergic reactions to peanut exposure; symptoms range from watery eyes toanaphylactic shock.[43] Thehygiene hypothesis of allergy states that a lack of early childhood exposure to infectious agents like germs and parasites could be causing the increase in food allergies.[44] Delaying exposure to peanuts in childhood can greatly increase the risk of developing allergy.[45][46] Peanut allergy has been associated with the use of skin preparations containing peanut oil among children, but the evidence is inconclusive. Peanut allergies are associated with family history and intake of soy products.[47] Refined peanut oil does not cause allergic reactions in most people with peanut allergies.[48] However, crude (unrefined) peanut oils contain protein, which may cause allergic reactions.[49][50]
Someschool districts in the U.S. and elsewhere have banned peanuts and products containing them.[51][52][53] However, a 2015 study in Canada found no difference in the percentage of accidental exposures occurring in schools prohibiting peanuts compared to schools allowing them.[54]
Some studies show that regular consumption of peanuts is associated with a lower specific risk ofmortality from certain diseases.[57][15] However, thestudy designs do not allowcause and effect to be inferred. According to the USFood and Drug Administration, "Scientific evidence suggests but does not prove that eating 1.5 ounces per day of most nuts (such as peanuts) as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease."[58]
Countering malnutrition
With their high protein concentration, peanuts are used to help reduce or preventmalnutrition.Plumpy Nut, MANA Nutrition, and Medika Mamba are high-protein, high-energy, and high-nutrient peanut-based pastes developed to be used as a therapeutic food by agencies includingUSAID to help infamine relief in developing countries.[59][60][61]
Peanuts can be used like other legumes and grains to make alactose-free,milk-like beverage,peanut milk, developed as a way to reduce malnutrition among children.[62]
Animal feed
Peanut plant tops and crop residues can be used forsilage.[63]
Theoilcake meal residue from oil processing is used as animal feed and soil fertilizer. Groundnut cake is a livestock feed, mostly used by cattle as protein supplements.[64] It is one of the most important and valuable feeds for all types of livestock and one of the most active ingredients for poultry rations.[65] Poor storage of the cake may sometimes result in its contamination byaflatoxin, a naturally occurringmycotoxin that is produced byAspergillus flavus andAspergillus parasiticus.[66] Some peanuts can be fed whole to livestock, for example, those over the peanut quota in the US or those with a higher aflatoxin content than that permitted by the food regulations.[67] Peanut processing often requires dehulling: the hulls generated in large amounts by the peanut industry can feed livestock, particularlyruminants.[68]
Edible products
Whole peanuts
Dry roasting is a common method of preparation, though the roast flavor is lost more quickly than with oil roasting or blister frying (oil roasting after soaking in water).[69]
Boiled peanuts are a popular snack in India, China, West Africa, and the southern United States. In the U.S. South, boiled peanuts are often prepared in briny water and sold in streetside stands.[70] Fresh "green" peanuts (not dehydrated) are ready for boiling; raw dehydrated peanuts must be rehydrated before boiling (usually in a bowl full of water overnight).[70]
Peanut oil is often used in cooking because it has a mild flavor and a relatively highsmoke point. Due to its highmonounsaturated content, it is considered more healthful thansaturated oils and is resistant torancidity. The several types of peanut oil include aromatic roasted peanut oil, refined peanut oil, extra virgin or cold-pressed peanut oil, and peanut extract. Refined peanut oil is exempt from allergen labeling laws in the U.S.[71]
A common cooking andsalad oil, peanut oil is 46% monounsaturated fats (primarilyoleic acid), 32%polyunsaturated fats (primarilylinoleic acid), and 17% saturated fats (primarilypalmitic acid) (source in nutrition table).[72] Extractable from whole peanuts using a simple water andcentrifugation method, the oil is being considered byNASA's Advanced Life Support program for future long-duration humanspace missions.[73]
Peanut butter is a foodpaste orspread made fromgrounddry roasted peanuts. It often contains additional ingredients that modify the taste or texture, such as salt, sweeteners, oremulsifiers. Many companies have added twists on traditionally plain peanut butter by adding various flavor varieties, such as chocolate, birthday cake, and cinnamon raisin.[74] Peanut butter is served as a spread on bread, toast or crackers, and used to make sandwiches (notably thepeanut butter and jelly sandwich). It is also used in a number of confections, such as peanut-flavoredgranola bars or croissants and other pastries. The United States is a leading exporter of peanut butter,[75] and itself consumes $800 million of peanut butter annually.[76]
Peanut protein concentrates and isolates are commercially produced from defatted peanut flour using several methods. Peanut flour concentrates (about 70% protein) are produced fromdehulled kernels by removing most of the oil and the water-soluble, non-protein components.Hydraulic pressing,screw pressing,solvent extraction, and pre-pressing followed by solvent extraction may be used for oil removal, after which protein isolation and purification are implemented.[78]
Edible products
Roasted peanuts as snack food
Roasting of peanuts in India
Peanut oil
Peanut butter
Roasted peanuts with shell
Sev mamra, puffed rice, peanuts and fried seasoned noodles
Peanuts are particularly common inPeruvian andMexican cuisine, both of which marry indigenous and European ingredients. For instance, in Peru, a popular traditional dish ispicante de cuy,[79] a roastedguinea pig served in a sauce of ground peanuts (ingredients native to South America) with roasted onions and garlic (ingredients from European cuisine). Also, in the Peruvian city ofArequipa, a dish calledocopa consists of a smooth sauce of roasted peanuts andhot peppers (both native to the region) with roasted onions, garlic, and oil, poured over meat or potatoes.[80] Another example is africassee combining a similar mixture with sautéed seafood or boiled and shredded chicken. These dishes are generally known asajíes, meaning "hot peppers", such asají de pollo andají de mariscos (seafoodajíes may omit peanuts). In Mexico, it is also used to prepare different traditional dishes, such as chicken in peanut sauce (encacahuatado), and is used as the main ingredient for the preparation of other famous dishes such as redpipián,mole poblano and oaxacanmole negro.[81]
Throughout the region, many candies and snacks are made using peanuts. In Mexico, it is common to find them in different presentations as a snack or candy: salty,"Japanese" peanuts,praline,enchilados or in the form of a traditional sweet made with peanuts and honey calledpalanqueta, and even as peanutmarzipan. There is a similar form of peanut candy in Brazil, calledpé-de-moleque, made with peanuts andmolasses, which resembles the Indianchikki in form.[82]
Southeast Asia
Fried peanuts in the Philippines
A Philippine dish using peanuts iskare-kare, with meat in a spicy peanut sauce.[83]
Peanuts are used in theMalian meat stewmaafe.[94] In Ghana, peanut butter is used forpeanut butter soupnkate nkwan.[95] Crushed peanuts may also be used for peanut candiesnkate cake andkuli-kuli, as well as other local foods such asoto.[95]
East Africa
Peanuts are a common ingredient of several relishes (dishes which accompanynshima) eaten inMalawi, and in the eastern part ofZambia, and these dishes are common throughout both countries. Thick peanut sauces are made inUganda to serve with rice and other starchy foods. Groundnut stew, calledebinyebwa in Uganda, is made by boiling ground peanut flour with other ingredients, such ascabbage,mushrooms, dried fish, meat or vegetables.[96]
North America
Fried curry peanuts
The state of Georgia leads the U.S. in peanut production, with 49 percent of the nation's peanut acreage and output. In 2014, farmers cultivated 591,000 acres of peanuts, yielding of 2.4 billion pounds. The most famous peanut farmer wasJimmy Carter ofSumter County, Georgia, who became the U.S. president in 1976.[97]
In the U.S. and Canada, peanuts are used in candies, cakes, and cookies. They are eatendry-roasted with or without salt. Ninety-five percent of Canadians eat them, with the average consumption of3 kilograms (6+1⁄2 lb) per person annually, while 79% of Canadians consume peanut butter weekly.[98] In the United States, peanut products are central in the diet, and are considered ascomfort foods.[99] Peanut butter represents half the American consumption and $850 million in annual retail sales.[100]Peanut soup is found on restaurant menus in the southeastern states.[101] In the southern U.S., peanuts are boiled for several hours until soft.[102] Peanuts can bedeep-fried, sometimes within the shell. Per person, Americans eat 2.7 kg (6 lb) of peanut products annually, at a retail cost of $2 billion.[100]
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