Walnut
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A walnut is the edible
seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...
of any tree of the genus '' Juglans'' (family
Juglandaceae The Juglandaceae are a plant family known as the walnut family. They are trees, or sometimes shrubs, in the order Fagales. Members of this family are native to the Americas, Eurasia, and Southeast Asia. The nine or ten genera in the family have ...
), particularly the Persian or English walnut, '' Juglans regia''. They are accessory fruit because the outer covering of the fruit is technically an involucre and thus not morphologically part of the carpel; this means it cannot be a
drupe In botany, a drupe (or stone fruit) is a type of fruit in which an outer fleshy part (exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pip'' (UK), ''pit'' (US), ''stone'', or ''pyrena'') of hardened endocarp with a seed ...
but is instead a drupe-like nut. After full ripening, the
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...
is discarded, and the kernel is eaten. Nuts of the eastern black walnut ('' Juglans nigra'') and butternuts ('' Juglans cinerea'') are less commonly consumed.


Description

Walnuts are the round, single-seed stone fruits of the walnut tree. They ripen between September and November in the northern hemisphere. The brown, wrinkly walnut shell is enclosed in a husk. Shells of walnuts available in commerce usually have two segments (but three or four-segment shells can also form). During the bumming process, the husk becomes brittle and the shell hard. The shell encloses the kernel or meat, which is usually in 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, preventing rancidity. Walnut trees are late to grow
leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...
, typically not doing so until more than halfway through the spring.


Chemistry

Walnut hulls contain diverse phytochemicals, such as polyphenols, that stain hands and can cause skin irritation. Seven phenolic compounds, including ferulic acid, vanillic acid, coumaric acid, syringic acid, myricetin, and juglone, were identified in walnut husks; juglone had concentrations of 2-4% fresh weight. Walnuts also contain the ellagitannin, pedunculagin. Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem bark of ''J. regia''.


Species

The three species of walnuts most commonly grown for their seeds are the Persian (or English) walnut ('' J. regia''), originating from Iran, the black walnut ('' J. nigra'') – native to eastern North America – and the Japanese walnut, also known as the heartnut ('' J. ailantifolia''). Other species include '' J. californica'', the California black walnut (often used as a rootstock 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). Numerous walnut cultivars have been developed commercially, which are nearly all hybrids of the English walnut.


Cultivation


History

During the Byzantine era, the walnut was also known by the name "royal nut". An article on walnut tree cultivation in Spain is included in
Ibn al-'Awwam Ibn al-'Awwam (), also called Abu Zakariya Ibn al-Awwam (), was an Al-Andalus agriculturist who flourished at Seville (modern-day southern Spain) in the later 12th century. He wrote a lengthy handbook on agriculture entitled in Arabic '' Kitāb al ...
's 12th-century ''Book on Agriculture''. The ''wal'' element in the name is Germanic and means ''foreign'', especially in the sense of ''Latin'' or ''non-Germanic''. Compare, for example,
Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...
, Walloons,
Wallachia Wallachia or Walachia (; ; : , : ) is a historical and geographical region of modern-day Romania. It is situated north of the Lower Danube and south of the Southern Carpathians. Wallachia was traditionally divided into two sections, Munteni ...
. The ''wal'' element is present in other Germanic-language words for the same nut, such as: German , Dutch , Danish , and Swedish .


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 carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...
. A batch that 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; walnuts are best stored below with low humidity. Temperatures above and humidity levels above 70 percent can lead to rapid and high spoilage losses. Above 75 percent humidity threshold, fungal molds that release aflatoxin can form.


Cultivars


Production

In 2022, world production of walnuts (in shell) was 3.9 million
tonnes The tonne ( or ; symbol: t) is a unit of mass equal to 1,000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...
, with China contributing 36% of the total (table). Other significant producers (in the order of decreasing harvest) were the United States,
Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
, and
Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
.


Nutrition

English walnuts without shells are 4% water, 15%
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
, 65% fat, and 14%
carbohydrates A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ma ...
, including 7%
dietary fiber Dietary fiber (fibre in English in the Commonwealth of Nations, Commonwealth English) 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 co ...
(table). In a reference amount of , walnuts provide and rich contents (20% or more of the Daily Value, DV) of several
dietary minerals In the context of nutrition, a mineral is a chemical element. Some "minerals" are essential for life, but most are not. ''Minerals'' are one of the four groups of essential nutrients; the others are vitamins, essential fatty acids, and essen ...
, particularly
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
at 148% DV, along with significant amounts of B vitamins (table). Unlike most nuts, which are high in monounsaturated fatty acids, walnut oil is composed largely of polyunsaturated fatty acids (72% of total fats), particularly alpha-linolenic acid (14%) and linoleic 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 due to the presence of impurities. In chemical terms, oleic acid is cl ...
as 13% of total fats (table source).


Health claims

In 2004, the US
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...
(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 and low
cholesterol Cholesterol is the principal sterol of all higher animals, distributed in body Tissue (biology), tissues, especially the brain and spinal cord, and in Animal fat, animal fats and oils. Cholesterol is biosynthesis, biosynthesized by all anima ...
diet and not resulting in increased caloric intake, may reduce the risk of coronary heart disease." At the same time, the agency refused to authorize the claim that "Diets including walnuts can reduce the risk of heart disease" and in 2010, it sent a warning letter to Diamond Foods stating there is "not sufficient evidence to identify a biologically active substance in walnuts that reduces the risk of coronary heart disease." In 2011, a scientific panel for the European Food Safety Authority recommended a health claim that "Walnuts contribute to the improvement of
endothelium The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the r ...
-dependent vasodilation" at a daily intake of ; it also found that a cause and effect relationship did not exist between consuming walnuts and reduction of blood LDL-cholesterol levels. The recommended health claim was later authorized by the
European Commission The European Commission (EC) is the primary Executive (government), executive arm of the European Union (EU). It operates as a cabinet government, with a number of European Commissioner, members of the Commission (directorial system, informall ...
.


Research

A 2020
systematic review A systematic review is a scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from published studies on ...
assessing the effect of walnut supplementation on
blood pressure Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...
found insufficient evidence to support walnut consumption as a blood pressure-lowering strategy. , the relationship between walnut consumption and cognitive health is inconclusive.


Uses


Culinary

Walnut meats are available in two forms: in their shells or de-shelled. Due to processing, the meats may be whole, halved, or in smaller portions. All walnuts can be eaten on their own (raw, toasted, or pickled), or as part of a mix such as
muesli Muesli ( ) is a cold Swiss cuisine, Swiss breakfast dish, the primary ingredient of which is rolled oats. Traditionally, it is set to soak in water overnight ("overnight oats") and eaten the next morning with fresh fruit, nuts, lemon juice, and ...
, or as an ingredient of a dish: e.g. walnut soup, walnut pie, walnut coffee cake, banana cake, brownie, fudge. 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, Circassian chicken, potica (a traditional festive pastry from
Slovenia Slovenia, officially the Republic of Slovenia, is a country in Central Europe. It borders Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the south and southeast, and a short (46.6 km) coastline within the Adriati ...
), satsivi (chicken in walnut sauce), tarator (a summer soup in Bulgarian cuisine), and poultry or meat ball
stew A stew is a combination of solid food ingredients that have been Cooking, cooked in Soup, liquid and served in the resultant gravy. Ingredients can include any combination of vegetables and may include meat, especially tougher meats suitable for ...
from
Iranian cuisine Iranian cuisine comprises the culinary traditions of Iran. Due to the historically common usage of the term "Name of Iran, Persia" to refer to Iran in the Western world,Yarshater, EhsaPersia or Iran, Persian or Farsi, ''Iranian Studies'', vol. ...
. Walnuts are also popular as an ice cream topping, and walnut pieces are used as a garnish on some foods. Nocino is a
liqueur A liqueur ( , ; ) is an alcoholic drink composed of Liquor, 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-age ...
made from unripe green walnuts steeped in
alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...
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 preparing salads of beans (e.g., three bean salad), noodle or pasta salads and antipasti, and forms of potato salad. A dressing may eve ...
. It has a low smoke point, which limits its use for frying.


Inks and dyes

Walnut husks can be used to make 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 1452 - 2 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 o ...
and
Rembrandt Rembrandt Harmenszoon van Rijn (; ; 15 July 1606 – 4 October 1669), mononymously known as Rembrandt was a Dutch Golden Age painter, printmaker, and Drawing, draughtsman. He is generally considered one of the greatest visual artists in ...
. Walnut husk pigments are used as a brown dye for fabric and were used in
classical Rome In modern historiography, ancient Rome is the Roman civilisation from the founding of the Italian 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 Kingd ...
and
medieval Europe In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of World history (field), global history. It began with the fall of the West ...
for dyeing hair.


Cleaning

The US Army 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 sur ...
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 originally developed by American rotorcraft company Piasecki Helicopter, Vertol and now manufactured by Boeing Defense, Space & Security. The Chinook is a Military transport helicopter, heav ...
helicopter crash (11 September 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. In the oil and gas industry, deep bed filters of ground walnut shell are used for "polishing" (filtering) oily contaminates from water.


Cat litter

At least two companies, LitterMaid and Naturally Fresh, make cat litter from ground walnut shells. Advantages cited over conventional clay litter include environmental sustainability of using what would otherwise be a waste product, superior natural biodegradability, and odor control as good or better than clay litter. Disadvantages include the possibility of allergic reactions among humans and cats.


Folk medicine

Walnuts have been listed as one of the 38 substances used to prepare Bach flower remedies, a herbal remedy promoted in folk medicine practices for its supposed effect on health. According to Cancer Research UK, "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer".


In culture

Large, symmetrically shaped, and sometimes intricately carved walnut shells (mainly from '' J. hopeiensis'') are valued collectibles in China where they are rotated in hand as a plaything or as decoration. They are also an investment and
status symbol A status symbol is a visible, external symbol of one's social position, an indicator of Wealth, economic or social status. Many luxury goods are often considered status symbols. ''Status symbol'' is also a Sociology, sociological term – as part ...
, with some carvings having high
monetary value In economics, economic value is a measure of the benefit provided by a goods, good or service (economics), service to an Agent (economics), economic agent, and value for money represents an assessment of whether financial or other resources are ...
if unique. Pairs of walnuts are sometimes sold in their green husks for a form of gambling known as ''du qing pi''.


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 utensil used to break the shell File:Benutzung eines Nussknackers.gif, Video of cracking a walnut File:Walnuts no shell.jpg, Walnut meats File:Gozinaki with walnuts.jpg, Georgian snack Gozinaki made from roasted walnuts and honey File:Applesauce walnut coffee cake.jpg,
Applesauce Apple sauce is a purée (not necessarily served as a true sauce) made of apples. It can be made with peeled or unpeeled apples and can be spiced or sweetened. Apple sauce is inexpensive and is widely consumed in North America and some parts of E ...
coffee cake garnished with walnuts File:A Pair Of Chnese Collectible Walnuts.jpg, Walnuts as collectibles File:Walnut murabba.jpg, Murabba made from young walnuts


See also

* Pickled walnuts


References


Further reading

* *


External links

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