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A walnut is the edible seed of a
drupe In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or ''pyrena'') of hardened endocarp with a seed (''kernel ...
of any
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
of the genus ''
Juglans Walnut trees are any species of tree in the plant genus ''Juglans'', the type genus of the family Juglandaceae, the seeds of which are referred to as walnuts. All species are deciduous trees, tall, with pinnate leaves , with 5–25 leaflets ...
'' (family Juglandaceae), particularly the Persian or English walnut, '' Juglans regia''. Although culinarily considered a "nut" and used as such, it is not a true botanical nut. After full ripening, the shell is discarded and the kernel is eaten. Nuts of the eastern black walnut (''
Juglans nigra ''Juglans nigra'', the eastern American black walnut, is a species of deciduous tree in the walnut family, Juglandaceae, native to North America. It grows mostly in riparian zones, from southern Ontario, west to southeast South Dakota, south ...
'') and butternuts ('' Juglans cinerea'') are less commonly consumed.


Characteristics

Walnuts are rounded, single-seeded stone fruits of the walnut tree commonly used for food after fully ripening between September and November, in which the removal of the husk at this stage reveals a browning wrinkly walnut shell, which is usually commercially found in two segments (three or four-segment shells can also form). During the ripening process, the husk will become brittle and the shell hard. The shell encloses the kernel or meat, which is usually made up of two halves separated by a membranous partition. The seed kernels – commonly available as shelled walnuts – are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen, thereby preventing rancidity. Walnut trees are late to grow leaves, typically not leafing out until more than halfway through the spring. They emit chemicals into the soil to prevent competing vegetation from growing. Because of this, susceptible plants should not be planted close to them.


History and cultivation

During the
Byzantine era The Byzantine calendar, also called the Roman calendar, the Creation Era of Constantinople or the Era of the World ( grc, Ἔτη Γενέσεως Κόσμου κατὰ Ῥωμαίους, also or , abbreviated as ε.Κ.; literal translation of ...
, the walnut was also known by the name "royal nut". An article on walnut tree cultivation in
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...
is included in Ibn al-'Awwam's 12th-century ''Book on Agriculture''. The walnut was originally known as the ''Welsh nut'', i.e. it came through France and/or Italy to Germanic speakers (German , Dutch or , Danish , Swedish ). In Polish translates to "Italian nuts" ( being the adjectival form of ("Italy")).


Types

The two most common major species of walnuts are grown for their seeds – the Persian or English walnut and the black walnut. The English walnut (''J. regia'') originated in
Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
(
Persia Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
), and the black walnut (''J. nigra'') is native to eastern
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
. The black walnut is of high flavor, but due to its hard shell and poor hulling characteristics it is not commercially cultivated in orchards. Numerous walnut
cultivars A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
have been developed commercially, which are nearly all hybrids of the English walnut. Other species include '' J. californica'', the
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
black walnut (often used as a
rootstock A rootstock is part of a plant, often an underground part, from which new above-ground growth can be produced. It could also be described as a stem with a well developed root system, to which a bud from another plant is grafted. It can refer to a ...
for commercial propagation of ''J. regia''), ''J. cinerea'' (butternuts), and ''J. major'', the Arizona walnut. Other sources list ''J. californica californica'' as native to southern California, and ''Juglans californica hindsii'', or just ''J. hindsii'', as native to northern California; in at least one case, these are given as "geographic variants" instead of subspecies (Botanica).


Production

In 2020, world production of walnuts (in shell) was 3.3 million
tonnes The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...
, with
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
contributing 33% of the total (table). Other major producers (in the order of decreasing harvest) were the United States,
Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
, and
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...
.


Storage

Walnuts, like other tree nuts, must be processed and stored properly. Poor storage makes walnuts susceptible to insect and fungal mold infestations; the latter produces aflatoxin – a potent carcinogen. A batch which contains mold-infested walnuts should be entirely discarded. The ideal temperature for the extended storage of walnuts is with low humidity for industrial and home storage. However, such refrigeration technologies are unavailable in developing countries where walnuts are produced in large quantities; there, walnuts are best stored below with low humidity. Temperatures above , and humidities above 70 percent can lead to rapid and high spoilage losses. Above 75 percent humidity threshold, fungal molds that release dangerous aflatoxin can form.


Food use

Walnut meats are available in two forms: in their shells or de-shelled. The meats may be whole, halved, or in smaller portions due to processing. All walnuts can be eaten on their own (raw, toasted or pickled), or as part of a mix such as muesli, or as an ingredient of a dish: e.g.
walnut soup Walnut soup is a broth-based or cream-based soup prepared using walnuts as a main ingredient. It is sometimes prepared in combinations using other ingredients, such as "pumpkin and walnut soup". Walnut soup is a part of the cuisines of China, Ital ...
, walnut pie, walnut coffee cake, banana cake, brownie,
fudge Fudge is a type of confection that is made by mixing sugar, butter and milk, heating it to the soft-ball stage at , and then beating the mixture while it cools so that it acquires a smooth, creamy consistency. In texture, this crystalline can ...
. Walnuts are often candied or pickled. Pickled walnuts that are the whole fruit can be savory or sweet depending on the preserving solution. Walnuts may be used as an ingredient in other foodstuffs. Walnut is an important ingredient in
baklava Baklava (, or ; ota, باقلوا ) is a layered pastry dessert made of filo pastry, filled with chopped nuts, and sweetened with syrup or honey. It was one of the most popular sweet pastries of Ottoman cuisine. The pre- Ottoman origin of t ...
,
Circassian chicken Circassian chicken ( Adyghe: ''Jed de ships sch'etu'') is a dish of shredded boiled chicken served under or in a rich paste made with crushed walnuts, and stock thickened with stale bread. Circassian Chicken is a classic Circassian dish, adopted ...
, chicken in walnut sauce, and poultry or meat ball
stew A stew is a combination of solid food ingredients that have been cooked in liquid and served in the resultant gravy. A stew needs to have raw ingredients added to the gravy. Ingredients in a stew can include any combination of vegetables a ...
from
Iranian cuisine Iranian cuisine () refers to the culinary practices of Iran. Due to the historically common usage of the term "Persia" to refer to Iran in the Western world,Yarshater, EhsaPersia or Iran, Persian or Farsi, ''Iranian Studies'', vol. XXII no. 1 ( ...
. Walnuts are also popular as an
ice cream Ice cream is a sweetened frozen food typically eaten as a snack or dessert. It may be made from milk or cream and is flavoured with a sweetener, either sugar or an alternative, and a spice, such as cocoa or vanilla, or with fruit such as ...
topping, and walnut pieces are used as a garnish on some foods. Nocino is a
liqueur A liqueur (; ; ) is an alcoholic drink composed of spirits (often rectified spirit) and additional flavorings such as sugar, fruits, herbs, and spices. Often served with or after dessert, they are typically heavily sweetened and un-aged beyon ...
made from unripe green walnuts steeped in
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
with syrup added. Walnut oil is available commercially and is chiefly used as a food ingredient particularly in
salad dressings A salad dressing is a sauce for salads. Used on virtually all '' leafy salads'', dressings may also be used in making salads of beans (such as three bean salad), noodle or pasta salads and antipasti, and forms of potato salad. Salad dressings ...
. It has a low smoke point, which limits its use for
frying Frying is the cooking of food in oil or another fat. Similar to sautéing, pan-fried foods are generally turned over once or twice during cooking to make sure that the food is well-made, using tongs or a spatula, while sautéed foods are co ...
.


Nutritional value

Walnuts without shells are 4% water, 15%
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
, 65% fat, and 14%
carbohydrates In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...
, including 7%
dietary fiber Dietary fiber (in British English fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition, and can be grouped generally by t ...
(table). In a 100-gram reference serving, walnuts provide and rich content (20% or more of the Daily Value or DV) of several
dietary minerals In the context of nutrition, a mineral is a chemical element required as an essential nutrient by organisms to perform functions necessary for life. However, the four major structural elements in the human body by weight (oxygen, hydrogen, carbon, ...
, particularly
manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
at 163% DV, and
B vitamins B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. Though these vitamins share similar names (B1, B2, B3, etc.), they are chemically distinct compounds that often coexi ...
(table). While English walnuts are the most commonly consumed, their nutrient density and profile are generally similar to those of black walnuts. Unlike most nuts, which are high in
monounsaturated fatty acids In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple est ...
, walnut oil is composed largely of
polyunsaturated fatty acids Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This class includes many important compounds, such as essential fatty acids and those that give drying oils their characteristic pr ...
(72% of total fats), particularly alpha-linolenic acid (14%) and
linoleic acid Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this acid. ...
(58%), although it does contain
oleic acid Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated o ...
as 13% of total fats.


Health claims

In 2016, the US
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
(FDA) provided a ''Qualified Health Claim'' allowing products containing walnuts to state: "Supportive but not conclusive research shows that eating per day of walnuts, as part of a low
saturated fat A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branche ...
and low
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
diet and not resulting in increased caloric intake, may reduce the risk of
coronary heart disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pl ...
." The FDA had, in 2004, refused to authorize the claim that "Diets including walnuts can reduce the risk of heart disease" and had sent an
FDA Warning Letter An FDA warning letter is an official message from the United States Food and Drug Administration (FDA) to a manufacturer or other organization that has violated some rule in a federally regulated activity. The FDA defines an FDA warning letter as ...
to Diamond Foods in 2010 stating there is "not sufficient evidence to identify a biologically active substance in walnuts that reduces the risk of coronary heart disease." A recent systematic review assessing the effect of walnut supplementation on blood pressure (BP) found insufficient evidence to support walnut consumption as a BP-lowering strategy. As of 2021, the relationship between walnuts and cognitive health is inconclusive.


Non-food applications

Juice from boiled walnuts can be used as an
antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as ...
agent. Green husks can be crushed and sprinkled into water to poison fish.


Folk medicine

Walnuts have been listed as one of the 38 substances used to prepare
Bach flower remedies Bach flower remedies (BFRs) are solutions of brandy and water—the water containing extreme dilutions of flower material developed by Edward Bach, an English homeopath, in the 1930s. Bach claimed that the dew found on flower petals retains ...
, a
herbal remedy Herbal medicine (also herbalism) is the study of pharmacognosy and the use of medicinal plants, which are a basis of traditional medicine. With worldwide research into pharmacology, some herbal medicines have been translated into modern remedies ...
promoted in folk medicine practices for its supposed effect on health. According to
Cancer Research UK Cancer Research UK (CRUK) is the world's largest independent cancer research organization. It is registered as a charity in the United Kingdom and Isle of Man, and was formed on 4 February 2002 by the merger of The Cancer Research Campaign and t ...
, "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer".


Inks and dyes

Walnut husks can be used to make a durable ink for writing and drawing. It is thought to have been used by artists including
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested on ...
and
Rembrandt Rembrandt Harmenszoon van Rijn (, ; 15 July 1606 – 4 October 1669), usually simply known as Rembrandt, was a Dutch Golden Age painter, printmaker and draughtsman. An innovative and prolific master in three media, he is generally cons ...
. Walnut husk pigments are used as a brown
dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...
for fabric and were used in
classical Rome In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 BC ...
and
medieval Europe In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
for dyeing hair.


Woodworking

The fine, straight-grained wood of the black walnut is highly valued as furniture wood, wall paneling, automobile interiors, and for gunstocks.


Cleaning

The
United States Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, ...
once used ground walnut shells for
abrasive blasting Sandblasting, sometimes known as abrasive blasting, is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface or remove su ...
to clean aviation parts because of low cost and low abrasive qualities. However, an investigation of a fatal
Boeing CH-47 Chinook The Boeing CH-47 Chinook is a tandem rotor helicopter developed by American rotorcraft company Vertol and manufactured by Boeing Vertol. The Chinook is a heavy-lift helicopter that is among the heaviest lifting Western helicopters. Its name, C ...
helicopter crash (September 11, 1982, in Mannheim, Germany) revealed that walnut shell grit had clogged an oil port, leading to the accident and the discontinuation of walnut shells as a cleaning agent. Commercially, crushed walnut shells are still used outside of aviation for low-abrasive, less-toxic cleaning and blasting applications.


Phytochemicals

Walnut hulls contain diverse phytochemicals, such as
polyphenols Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...
that stain hands and can cause skin irritation. Seven phenolic compounds, including
ferulic acid Ferulic acid is a hydroxycinnamic acid, an organic compound with the formula (CH3O)HOC6H3CH=CHCO2H. The name is derived from the genus ''Ferula'', referring to the giant fennel ('' Ferula communis''). Classified as a phenolic phytochemical, ferul ...
,
vanillic acid Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is a dihydroxybenzoic acid derivative used as a flavoring agent. It is an oxidized form of vanillin. It is also an intermediate in the production of vanillin from ferulic acid. Occurrence in natu ...
,
coumaric acid Coumaric acid is a phenolic derivative of cinnamic acid Cinnamic acid is an organic compound with the formula C6H5-CH=CH- COOH. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents. Cl ...
,
syringic acid Syringic acid is a naturally occurring phenolic compound and dimethoxybenzene that is commonly found as a plant metabolite. Natural occurrence Syringic acid can be found in several plants including ''Ardisia elliptica'' and '' Schumannianthus ...
,
myricetin Myricetin is a member of the flavonoid class of polyphenolic compounds, with antioxidant properties. Common dietary sources include vegetables (including tomatoes), fruits (including oranges), nuts, berries, tea, and red wine. Myricetin is struc ...
, and
juglone Juglone, also called 5-hydroxy-1,4-naphthalenedione (IUPAC) is an organic compound with the molecular formula C10H6O3. In the food industry, juglone is also known as C.I. Natural Brown 7 and C.I. 75500. It is insoluble in benzene but soluble i ...
were identified in walnut husks. Juglone, the predominant phenolic, was found in concentrations of 2-4% fresh weight. Walnuts also contain the ellagitannin
pedunculagin Pedunculagin is an ellagitannin. It is formed from casuarictin via the loss of a gallate group. Natural occurrence Pedunculagin is found in plants in orders in the clade Rosidae. It can be found the pericarp of pomegranates (''Punica granatum ...
. Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem bark of ''J. regia''.


Chinese culture

Large, symmetrically shaped, and sometimes intricately carved walnut shells (mainly from '' J. hopeiensis'' ) are valued collectibles in China where they are rotated in the hand as a plaything or as decoration. They are also an
investment Investment is the dedication of money to purchase of an asset to attain an increase in value over a period of time. Investment requires a sacrifice of some present asset, such as time, money, or effort. In finance, the purpose of investing i ...
and status symbol, with some carvings having high
monetary value In economics, economic value is a measure of the benefit provided by a good or service to an economic agent. It is generally measured through units of currency, and the interpretation is therefore "what is the maximum amount of money a speci ...
if unique. Pairs of walnuts are sometimes sold in their green husks for a form of gambling known as ''du qing pi''.


Cultivars


Gallery

File:Juglans regia 2009 G2.jpg, Common walnut in growth File:California Blackwalnut.jpg, California black walnut in growth File:Juglans regia polyploid fruit bottom.jpg, A three-segment shell which occurs rarely File:Noix3coquilles.jpg, Walnut in shell and a
nutcracker A nutcracker is a tool designed to open nuts by cracking their shells. There are many designs, including levers, screws, and ratchets. The lever version is also used for cracking lobster and crab shells. A decorative version portrays a person w ...
utensil used to break the shell File:Benutzung eines Nussknackers.gif, Video of cracking a walnut File:Walnuts no shell.jpg, Walnut meats File:Cerneaux de noix.jpg, Broken walnut meats File:Gozinaki with walnuts.jpg,
Georgian Georgian may refer to: Common meanings * Anything related to, or originating from Georgia (country) ** Georgians, an indigenous Caucasian ethnic group ** Georgian language, a Kartvelian language spoken by Georgians **Georgian scripts, three scrip ...
snack
Gozinaki Gozinaki or Gozinaqi ( ka, გოზინაყი ) is a traditional Georgian confection made of caramelized nuts, usually walnuts, fried in honey, and served exclusively on New Year's Eve and Christmas. In the western Georgian provinces of I ...
made from roasted walnuts and honey File:Applesauce walnut coffee cake.jpg,
Applesauce Apple sauce or applesauce is a purée (not necessarily served as a true sauce) made of apples. It can be made with peeled or unpeeled apples and may be spiced or sweetened. Apple sauce is inexpensive and is widely consumed in North America and s ...
coffee cake Coffee cake may refer to a sponge cake flavored with coffee or, in the United States, a sweet cake intended to be eaten with coffee or tea (similar to tea cake). A coffee-flavored cake is typically baked in a circular shape with two layers sep ...
garnished with walnuts File:A Pair Of Chnese Collectible Walnuts.jpg, Walnuts as collectibles File:Walnut murabba.jpg,
Murabba Murabba (from ar, مربى) refers to a sweet fruit preserve which is popular in many regions of South Caucasus, Central Asia, South Asia, and the Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolit ...
made from young walnuts


See also

* Kurumi * List of unproven and disproven cancer treatments


References


Further reading

* *


External links

* {{Nuts Crops Edible nuts and seeds Fruit trees Plant dyes Symbols of California