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{{Short description|Nut of any tree of the genus Juglans}}
{{wikt|walnut}}
{{about|walnuts as food|the genus|Juglans|walnut wood (timber)|Juglans#Wood|other uses}}
{{Use dmy dates|date=January 2023}}
[[File:Walnuts - whole and open with halved kernel.jpg|thumb|Walnuts]]

[[File:Inside of a walnut in growth.jpg|thumb|upright|Inside of a walnut in growth]]
[[File:Three-part Walnut-8283.jpg|thumb|upright|Three-segment walnut]]
[[File:Juglans regia Echte Walnußfrucht 2.JPG|right|thumb|Walnut shell inside its green husk]]
[[File:Adriaen Coorte - Two Walnuts.jpg|thumb|right|Artistic depiction of two walnuts ([[Adriaen Coorte]], 1702)]]
A '''walnut''' is the edible seed of any tree of the genus ''[[Juglans]]'' (family [[Juglandaceae]]), particularly the Persian or English walnut, ''[[Juglans regia]]''. The [[Mast (botany)|fruits of trees]] in the family [[Juglandaceae]] are often confused with [[drupes]]. Still, they are [[accessory fruit]] because the outer covering of the fruit is technically an [[Involucral bract|involucre]] and thus not morphologically part of the carpel; this means it cannot be a drupe but is instead a drupe-like nut.

After full ripening, the [[husk|shell]] is discarded, and the kernel is eaten. Nuts of the eastern black walnut (''[[Juglans nigra]]'') and butternuts (''[[Juglans cinerea]]'') are less commonly consumed.

== Characteristics ==
Walnuts are the round, single-seed [[Drupe|stone fruits]] of the walnut tree. They are commonly used for food. They ripen between September and November in the northern hemisphere. The brown, wrinkly walnut shell is enclosed in a husk.<ref name="GKH">{{Cite web |last=Grant |first=Amy |date=19 April 2021 |title=Walnut Tree Harvesting: When Are Walnuts Ready To Pick |url=https://www.gardeningknowhow.com/edible/nut-trees/walnut/walnut-tree-harvesting.htm |access-date=4 December 2021 |website=Gardening Know How}}</ref> Shells of walnuts available in commerce usually have two segments (but three or four-segment shells can also form). During the ripening 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.<ref name="GKH" /> 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 [[rancidification|rancidity]].<ref name="wde1" />

Walnut trees are late to grow leaves, typically not leafing until more than half way through the spring.

== History, cultivation, and etymology ==
During the [[Byzantine era]], the walnut was also known by the name "royal nut".<ref>{{Cite book |url=https://archive.org/details/Geoponica02/page/n13/mode/1up |title=Geoponika - Agricultural Pursuits |date=1806 |publisher=University of Oxford |volume=2 |location=London |language=en |translator-last=Owen |translator-first=Thomas |translator-link=Thomas Owen (priest)}}</ref> An article on walnut tree cultivation in Spain is included in [[Ibn al-'Awwam]]'s 12th-century ''Book on Agriculture''.<ref>{{Cite book |last=Ibn al-ʻAwwām |first=Yaḥyá ibn Muḥammad |url=https://archive.org/details/lelivredelagric00algoog/page/n14/mode/2up |title=Le livre de l'agriculture d'Ibn-al-Awam (kitab-al-felahah) |publisher=A. Franck |year=1864 |location=Paris |pages=271–276 (ch. 7 - Article 24) |language=fr |translator-last=Clement-Mullet |translator-first=Jean Jacques |oclc=780050566 |author-link=Ibn al-'Awwam}}</ref>{{Anchor|walnut}} The ''wal'' element in the name is Germanic and means ''foreign'', especially in the sense of ''Latin'' or ''non-Germanic''. Compare, for example, [[Wales]], [[Walloons]], [[Wallachia]]. The ''wal'' element is present in other Germanic-language words for the same nut, such as: German {{Lang|de|Walnuss}}, Dutch {{Lang|nl|walnoot}}, Danish {{Lang|da|valnød}}, and Swedish {{Lang|sv|valnöt}}.

== Types ==
The three species of walnuts most commonly grown for their seeds are the Persian (or English) walnut (''[[Juglans regia|J. regia]]''), originating from Iran, the black walnut (''[[Juglans nigra|J. nigra]]'') – native to eastern North America – and the Japanese walnut, also known as the heartnut (''[[Juglans ailantifolia|J. ailantifolia]]'').<ref>{{cite book |url=https://books.google.com/books?id=nyWY_YkV7qAC&pg=PA545 |page=545 |title=Top 100 Food Plants |author=Ernest Small |publisher=NRC Research Press |year=2009|isbn=9780660198583 }}</ref> Other species include ''[[Juglans californica|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).{{Cn|date=January 2021}}

Numerous walnut [[cultivars]] have been developed commercially, which are nearly all hybrids of the English walnut.<ref>{{Cite web |year=2006 |title=Commodity Profile: English Walnuts |url=http://aic.ucdavis.edu/profiles/Walnut-2006.pdf |url-status=live |archive-url=http://archive.wikiwix.com/cache/20120312092338/http://aic.ucdavis.edu/profiles/Walnut-2006.pdf |archive-date=12 March 2012 |publisher=AgMRC, University of California}}</ref>

The black walnut is of strong flavor, but due to its hard shell and poor hulling characteristics, it is not commercially cultivated in orchards.{{cn|date=June 2023}}

{| class="wikitable" style="float:right; clear:right; width:14em; margin:1em; text-align:center;"
|+ Walnut production – 2021
! scope="col" | Country
! scope="col" | Production (millions of [[tonne]]s)
|-
| {{CHN}} || 1.10
|-
| {{USA}} || 0.66
|-
| {{IRN}} || 0.39
|-
| {{TUR}} || 0.33
|-
| {{MEX}} || 0.14
|-
| '''World''' || '''3.50'''
|-
| colspan="2" |Source: [[FAOSTAT]] of the United Nations<ref name="faostat">{{Cite web |year=2023 |title=Walnut (in shell) production in 2021, Crops/Regions/World list/Production Quantity (pick lists) |url=http://www.fao.org/faostat/en/#data/QC |access-date=9 July 2023 |publisher=UN Food and Agriculture Organization, Corporate Statistical Database (FAOSTAT)}}</ref>
|}

== Production ==
In 2021, world production of walnuts (in shell) was 3.5 million [[tonnes]], with China contributing 31% of the total (table). Other major producers (in the order of decreasing harvest) were the United States, [[Iran]], and [[Turkey]].<ref name=faostat/>

== 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 that contains mold-infested walnuts should be entirely discarded.<ref name="wde1">{{Cite web |year=2010 |title=Walnut; Agriculture – Transport Information Service |url=http://www.tis-gdv.de/tis_e/ware/nuesse/walnuss/walnuss.htm#toxizitaet |url-status=live |archive-url=https://web.archive.org/web/20150214032218/http://www.tis-gdv.de/tis_e/ware/nuesse/walnuss/walnuss.htm#toxizitaet |archive-date=14 February 2015 |publisher=Association for German Insurance}}</ref>

The ideal temperature for the extended storage of walnuts is {{convert|-3|to|0|C}} 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 {{convert|25|C}} with low humidity. Temperatures above {{convert|30|C}} and humidity levels above 70 percent can lead to rapid and high spoilage losses. Above 75 percent humidity threshold, fungal molds that release dangerous aflatoxin can form.<ref name="wde1" /><ref>{{Cite web |year=1998 |title=Food, Nutrition & Agriculture – Prevention of aflatoxin |url=http://www.fao.org/DOCREP/W9474T/W9474T06.HTM |url-status=live |archive-url=https://web.archive.org/web/20110307103138/http://www.fao.org/docrep/w9474t/w9474t06.htm |archive-date=7 March 2011 |publisher=FAO, United Nations}}</ref>

== Food use ==
[[File:Walnuts in their shells available for sale.jpg|thumb|Walnuts in their shells available for sale in a supermarket in the United States]]
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]], or as an ingredient of a [[Dish (food)|dish]]: e.g. [[walnut soup]], [[walnut pie]], [[coffee cake|walnut coffee cake]], [[Banana cake#Preparation|banana cake]], [[Chocolate brownie#History|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]], [[satsivi|chicken in walnut sauce]], [[tarator]] a summer soup in Bulgarian cuisine, and [[fesenjan|poultry or meat ball]] [[khoresh|stew]] from [[Iranian cuisine]].

Walnuts are also popular as an [[ice cream]] topping, and walnut pieces are used as a [[Garnish (food)|garnish]] on some foods.<ref>{{Cite book |last1=Forsberg |first1=B. |url=https://books.google.com/books?id=i-VkDQAAQBAJ&pg=PA98 |title=The Complete Idiot's Guide to Terrific Diabetic Meals |last2=Clark-Warner |first2=M.S.R.D.C.D.E. |last3=Beale |first3=L. |publisher=DK Publishing |year=2004 |isbn=978-1-61564-486-5 |page=98 |access-date=27 May 2017 |archive-url=https://web.archive.org/web/20180331230045/https://books.google.com/books?id=i-VkDQAAQBAJ&pg=PA98 |archive-date=31 March 2018 |url-status=live}}</ref>

[[Nocino]] is a [[liqueur]] made from unripe green walnuts steeped in [[ethanol|alcohol]] with syrup added.

[[Walnut oil]] is available commercially and is chiefly used as a food ingredient, particularly in [[salad#dressings|salad dressings]]. It has a low [[smoke point]], which limits its use for [[frying]].<ref>{{Cite web |title=Walnut oil recipes |url=https://www.bbc.co.uk/food/walnut_oil |url-status=live |archive-url=https://web.archive.org/web/20140217191658/http://www.bbc.co.uk/food/walnut_oil |archive-date=17 February 2014 |access-date=3 July 2014 |publisher=BBC}}</ref><ref>{{Cite web |last=Turner |first=Lisa |title=Oil Change |url=http://www.betternutrition.com/five-essential-oils/food/offtheshelf/963 |url-status=dead |archive-url=https://web.archive.org/web/20140706152519/http://www.betternutrition.com/five-essential-oils/food/offtheshelf/963 |archive-date=6 July 2014 |access-date=5 July 2014 |website=Better Nutrition}}</ref>

=== Nutritional value ===
{{Nutritional value
| name = Walnut, English
| image = Whole Walnut Kernel.jpg
| image_size = 100px
| caption = Walnut kernel, halves
| serving_size = 100 grams
| kJ = 2738
| carbs = 13.71 g
| fat = 65.21 g
| protein = 15.23 g
| sugars = 2.61 g
| satfat = 6.126 g
| transfat =
| monofat = 8.933 g
| polyfat = 47.174 g
| omega3fat = 9 g
| omega6fat = 38 g
| fiber = 6.7 g
| starch = 0.06 g
| water = 4.07 g
| calcium_mg = 98
| iron_mg = 2.91
| phosphorus_mg = 346
| magnesium_mg = 158
| manganese_mg = 3.414
| sodium_mg = 2
| potassium_mg = 441
| zinc_mg = 3.09
| vitA_ug = 1
| vitA_iu = 20
| betacarotene_ug = 12
| lutein_ug = 9
| thiamin_mg = 0.341
| riboflavin_mg = 0.15
| niacin_mg = 1.125
| pantothenic_mg = 0.570
| vitB6_mg = 0.537
| folate_ug = 98
| vitB12_ug = 0
| vitC_mg = 1.3
| vitE_mg = 0.7
| vitK_ug = 2.7
| source_usda = 1
| note = [https://fdc.nal.usda.gov/fdc-app.html#/?query=ndbNumber:12155 Link to Full USDA Database Entry]
}}

Walnuts without shells are 4% water, 15% [[protein]], 65% fat, and 14% [[carbohydrates]], including 7% [[dietary fiber]]. In a 100-gram reference serving, walnuts provide {{convert|654|kcal|kJ|order=flip}} and "rich" amounts (20% or more of the [[Daily Value]] or DV) of several [[dietary minerals]], particularly [[manganese]] at 163% DV; along with significant amounts of [[B vitamins]].<ref name=USDA_table>{{cite web |title=FoodData Central: Nuts, walnuts, English, halves, raw |author=[[U.S. Department of Agriculture]] |url=https://fdc.nal.usda.gov/fdc-app.html#/food-details/2346394/nutrients |website=fdc.nal.usda.gov |date=2018-10-28 |access-date=2023-06-27}}</ref>

While English walnuts are the most commonly consumed, their nutrient density and profile are generally similar to those of black walnuts.<ref name="nd1">{{Cite web |title=Nutrition facts: Nuts, walnuts, English dried per 100 g |url=http://nutritiondata.self.com/facts/nut-and-seed-products/3138/2 |url-status=live |archive-url=https://web.archive.org/web/20140705192121/http://nutritiondata.self.com/facts/nut-and-seed-products/3138/2 |archive-date=5 July 2014 |access-date=4 July 2014}}</ref><ref>{{Cite web |title=Nutrition facts: Nuts, walnuts, black, dried per 100 g |url=http://nutritiondata.self.com/facts/nut-and-seed-products/3137/2 |url-status=live |archive-url=https://web.archive.org/web/20140705164140/http://nutritiondata.self.com/facts/nut-and-seed-products/3137/2 |archive-date=5 July 2014 |access-date=4 July 2014}}</ref>

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]] as 13% of total fats.<ref name="nd1" />

=== Health claims ===
In 2016, the US [[Food and Drug Administration]] (FDA) provided a [[health claim|''Qualified Health Claim'']] allowing products containing walnuts to state: "Supportive but not conclusive research shows that eating {{convert|1.5|oz|g}} per day of walnuts, as part of a low [[saturated fat]] and low [[cholesterol]] diet and not resulting in increased caloric intake, may reduce the risk of [[coronary heart disease]]."<ref>{{Cite web |date=9 March 2004 |title=Qualified Claims About Cardiovascular Disease Risk: Walnuts & Heart Disease Docket No. 02P-0292 |url=https://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm073992.htm#cardio |url-status=live |archive-url=https://web.archive.org/web/20161027214329/https://www.fda.gov/food/ingredientspackaginglabeling/labelingnutrition/ucm073992.htm#cardio |archive-date=27 October 2016 |access-date=1 November 2016 |publisher=US Food and Drug Administration}}</ref> The FDA had, in 2004, refused to authorize the claim that "Diets including walnuts can reduce the risk of heart disease"<ref>{{Cite web |last=Tarantino |first=Laura M. |date=9 March 2004 |title=Qualified Health Claims: Letter of Enforcement Discretion – Walnuts and Coronary Heart Disease (Docket No 02P-0292) |url=https://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm072910.htm |url-status=live |archive-url=https://web.archive.org/web/20170507025833/https://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm072910.htm |archive-date=7 May 2017 |access-date=30 April 2017 |publisher=US Food and Drug Administration, Labeling and Nutrition}}</ref> and had sent an [[FDA Warning Letter]] 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."<ref>{{Cite web |last=Wagner |first=Roberta |date=22 February 2010 |title=FDA Warning Letter to Diamond Food, Inc |url=https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2010/ucm202825.htm |url-status=dead |archive-url=https://wayback.archive-it.org/7993/20170112194904/https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2010/ucm202825.htm |archive-date=12 January 2017 |access-date=1 November 2016 |publisher=US Food and Drug Administration, Inspections, Compliance, Enforcement, and Criminal Investigations |quote=the evidence supporting a relationship between walnuts and coronary heart disease is related to the omega-3 fatty acid content of walnuts. There is not sufficient evidence to identify a biologically active substance in walnuts that reduces the risk of coronary heart disease. Therefore, the above statement is an unauthorized health claim}}</ref> 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.<ref>{{Cite journal |last1=Li |first1=Jiayang |last2=Jiang |first2=Bo |last3=O. Santos |first3=Heitor |last4=Santos |first4=Dinamene |last5=Singh |first5=Ambrish |last6=Wang |first6=Lei |date=November 2020 |title=Effects of walnut intake on blood pressure: A systematic review and meta‐analysis of randomized controlled trials |url=https://onlinelibrary.wiley.com/doi/10.1002/ptr.6740 |journal=Phytotherapy Research |language=en |volume=34 |issue=11 |pages=2921–2931 |doi=10.1002/ptr.6740 |pmid=32510725 |s2cid=219539797 |issn=0951-418X}}</ref> It has been studied if walnuts may enhance the probability of pregnancy for men with male factor infertility.<ref>{{Cite web |year=2019 |title=Randomized Clinical Trial: Effect of Walnuts on Semen Parameters and Male Fertility (P18-042-19) |url=https://academic.oup.com/cdn/article/3/Supplement_1/nzz039.P18-042-19/5517354 |access-date=8 January 2023 |website=academic.oup.com}}</ref>

As of 2021, the relationship between walnuts and cognitive health is inconclusive.<ref>{{Cite journal |last1=Cahoon |first1=Danielle |last2=Shertukde |first2=Shruti P. |last3=Avendano |first3=Esther E. |last4=Tanprasertsuk |first4=Jirayu |last5=Scott |first5=Tammy M. |last6=Johnson |first6=Elizabeth J. |last7=Chung |first7=Mei |last8=Nirmala |first8=Nanguneri |date=1 January 2021 |title=Walnut intake, cognitive outcomes and risk factors: a systematic review and meta-analysis |journal=Annals of Medicine |publisher=Informa UK Limited |volume=53 |issue=1 |pages=972–998 |doi=10.1080/07853890.2021.1925955 |issn=0785-3890 |pmc=8211141 |pmid=34132152}}</ref>

== Non-food applications ==
Juice from boiled walnuts can be used as an [[antifungal]] agent. Green husks can be crushed and sprinkled into the water to [[Fish toxins|poison fish]].<ref>{{Cite book |url=https://www.worldcat.org/oclc/277203364 |title=The Complete Guide to Edible Wild Plants |publisher=[[Skyhorse Publishing]] |year=2009 |isbn=978-1-60239-692-0 |location=New York |pages=107 |language=en-US |oclc=277203364}}</ref>

=== Folk medicine ===
Walnuts have been listed as one of the 38 substances used to prepare [[Bach flower remedies]],<ref name="Vohra2004">{{Cite book |last=Vohra |first=D. S. |url=https://books.google.com/books?id=icG8onA0ys8C&pg=PR3 |title=Bach Flower Remedies: A Comprehensive Study |date=1 June 2004 |publisher=B. Jain Publishers |isbn=978-81-7021-271-3 |page=3 |access-date=2 September 2013 |archive-url=https://web.archive.org/web/20131231084700/http://books.google.com/books?id=icG8onA0ys8C&pg=PR3 |archive-date=31 December 2013 |url-status=live}}</ref> a [[pseudoscience|herbal remedy]] promoted in [[traditional medicine|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".<ref>{{Cite web |date=26 January 2015 |title=Flower remedies |url=http://www.cancerresearchuk.org/cancer-help/about-cancer/treatment/complementary-alternative/therapies/flower-remedies |url-status=live |archive-url=https://web.archive.org/web/20130911224802/http://www.cancerresearchuk.org/cancer-help/about-cancer/treatment/complementary-alternative/therapies/flower-remedies |archive-date=11 September 2013 |access-date=1 September 2013 |publisher=[[Cancer Research UK]]}}</ref>

=== Inks and dyes ===
{{Further|Walnut ink}}
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]] and [[Rembrandt]].<ref>{{Cite web |date=October 2002 |title=Black Walnut Ink Workshop |url=http://www.gnsi.science-art.com/GNSIDC/reports/2002Oct/Oct2002.html |url-status=live |archive-url=https://web.archive.org/web/20141009140617/http://www.gnsi.science-art.com/GNSIDC/reports/2002Oct/Oct2002.html |archive-date=9 October 2014 |access-date=3 July 2014 |publisher=Guild of Natural Science Illustrators}}</ref>

Walnut husk pigments are used as a brown [[Natural dye|dye]] for fabric<ref>{{Cite web |date=13–16 November 1997 |title=The Colors of Invention – How to Dye Fibers Naturally |url=http://invention.smithsonian.org/centerpieces/whole_cloth/u3tc/u3materials/dyenatural.html |url-status=live |archive-url=https://web.archive.org/web/20141021211128/http://invention.smithsonian.org/centerpieces/whole_cloth/u3tc/u3materials/dyenatural.html |archive-date=21 October 2014 |access-date=3 July 2014 |publisher=Smithsonian Museum}}</ref> and were used in [[classical Rome]] and [[medieval Europe]] for [[Hair coloring|dyeing hair]].<ref>{{Cite book |last=Sherrow |first=Victoria |url=https://archive.org/details/encyclopediaofha0000sher |title=Encyclopedia of Hair: A Cultural History |date=2006 |publisher=Greenwood Publishing Group |isbn=978-0-313-33145-9 |pages=[https://archive.org/details/encyclopediaofha0000sher/page/267 267], 355 |quote=walnut. |access-date=3 July 2014 |url-access=registration}}</ref>

==={{anchor|Wood|Woodworking}} Woodworking===
The fine, straight-grained wood of the black walnut is highly valued for furniture, wall paneling, automobile interiors, and [[Stock (firearms)|gunstocks]].<ref>{{Cite web |last=Williams |first=Robert D. |year=1980 |title=Black walnut |url=https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/juglans/nigra.htm |access-date=29 August 2021 |publisher=US Department of Agriculture}}</ref>

=== Cleaning ===
The [[United States Army]] once used ground walnut shells for [[abrasive blasting]] to clean aviation parts because of low cost and low abrasive qualities. However, an investigation of a fatal [[Boeing CH-47 Chinook]] 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.<ref>{{Cite web |year=1985 |title=In Re Air Crash Disaster at Mannheim Germany on 9/11/82. Ursula J. Schoenborn, As Executrix of the Estate of Leonedward Schoenborn, Deceased, v. the Boeing Company. Appeal of the Boeing Company. United States Court of Appeals, Third Circuit. 769 F.2d 115 |url=http://law.justia.com/cases/federal/appellate-courts/F2/769/115/197097/ |url-status=live |archive-url=https://web.archive.org/web/20140517151311/http://law.justia.com/cases/federal/appellate-courts/F2/769/115/197097/ |archive-date=17 May 2014 |access-date=10 April 2014 |publisher=Justia}}</ref>

Commercially, crushed walnut shells are still used outside of aviation for low-abrasive, less-toxic cleaning and blasting applications.<ref>{{Cite news |title=OSHA fact sheet addresses abrasive blasting hazards |language=en |url=https://www.safetyandhealthmagazine.com/articles/9596-osha-fact-sheet-addresses-abrasive-blasting-hazards |access-date=20 August 2018}}</ref> In the oil and gas industry, [[Nut shell filter|deep bed filters]] of ground walnut shell are used for "polishing" (filtering) oily contaminates from water.<ref>{{cite book |last1=Cheremisinoff |first1=Nicholas P. |title=Perfluorinated chemicals (PFCs) : contaminants of concern |date=2017 |publisher=[[Wiley (publisher)|Wiley]] |location=Hoboken, New Jersey |isbn=978-1-119-36353-8 |page=194}}</ref>

=== Cat litter ===
At least two companies, LitterMaid and Naturally Fresh, make [[cat litter]] from ground walnut shells.<ref>{{cite news|url=https://www.insider.com/guides/pets/best-natural-cat-litter|title=The best natural cat litter we tested with our pets|work=Insider|date=24 October 2022|first=Shoshi|last=Parks}}</ref><ref>{{cite news|url=https://journalnow.com/lifestyles/pets/what-is-the-best-walnut-cat-litter/article_3d870070-7673-50b7-a7a0-5153178b5781.html|title=What is the best walnut cat litter|work=Winston-Salem Journal|date=26 May 2023|author=n.a.}}</ref> 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.<ref>{{cite news|url=https://buffalonews.com/lifestyles/pets/what-are-the-pros-of-walnut-cat-litter/article_e72fa3f3-7fb5-52e0-be66-cb42d0a52fbe.html|title=What are the pros of walnut cat litter?|work=Buffalo News|date=26 May 2023|author=n.a.}}</ref> Disadvantages include the possibility of allergic reactions among humans and cats.<ref>{{cite news|url=https://scnow.com/lifestyles/pets/what-are-the-cons-of-walnut-cat-litter/article_5a494202-7aca-5dd2-bb9d-648603fbc08b.html|title=What are the cons of walnut cat litter?|work=SCNow|date=26 May 2023|author=n.a.}}</ref>

== Phytochemicals ==
Walnut hulls contain diverse [[phytochemical]]s, 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.<ref>{{Cite journal |last1=Cosmulescu |first1=Sina Niculina |last2=Trandafir |first2=Ion |last3=Achim |first3=Gheorghe |last4=Botu |first4=Mihai |last5=Baciu |first5=Adrian |last6=Gruia |first6=Marius |date=15 June 2010 |title=Phenolics of Green Husk in Mature Walnut Fruits |url=http://www.notulaebotanicae.ro/index.php/nbha/article/view/4624 |url-status=live |journal=Notulae Botanicae Horti Agrobotanici Cluj-Napoca |volume=38 |issue=1 |pages=53–56 |issn=1842-4309 |archive-url=https://web.archive.org/web/20170729032755/http://www.notulaebotanicae.ro/index.php/nbha/article/view/4624 |archive-date=29 July 2017}}</ref>

Walnuts also contain the ellagitannin, [[pedunculagin]].<ref>{{Cite journal |last1=Cerdá |first1=Begoña |last2=Tomás-Barberán |first2=Francisco A. |last3=Espín |first3=Juan Carlos |date=2005-01-01 |title=Metabolism of Antioxidant and Chemopreventive Ellagitannins from Strawberries, Raspberries, Walnuts, and Oak-Aged Wine in Humans: Identification of Biomarkers and Individual Variability |url=https://pubs.acs.org/doi/10.1021/jf049144d |journal=Journal of Agricultural and Food Chemistry |language=en |volume=53 |issue=2 |pages=227–235 |doi=10.1021/jf049144d |pmid=15656654 |issn=0021-8561}}</ref> Regiolone has been isolated with juglone, [[betulinic acid]] and [[sitosterol]] from the stem bark of ''J. regia''.<ref>{{Cite journal |last1=Talapatra |first1=Sunil K. |last2=Karmacharya |first2=Bimala |last3=De |first3=Shambhu C. |last4=Talapatra |first4=Bani |date=January 1988 |title=(−)-Regiolone, an α-tetralone from Juglans regia: structure, stereochemistry and conformation |url=https://linkinghub.elsevier.com/retrieve/pii/0031942288830474 |journal=Phytochemistry |language=en |volume=27 |issue=12 |pages=3929–3932 |doi=10.1016/0031-9422(88)83047-4|bibcode=1988PChem..27.3929T }}</ref>

== Chinese culture ==
Large, symmetrically shaped, and sometimes intricately carved walnut shells (mainly from ''[[Juglans hopeiensis|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]], with some carvings having high [[value (economics)|monetary value]] if unique.<ref>{{Cite web |last1=Subler |first1=Jason |last2=Lee |first2=Jane Lanhee |date=28 August 2012 |title=Status-conscious investors shell out on great walnuts of China |url=https://www.reuters.com/article/us-china-walnuts-idUSBRE87R0NV20120828 |url-status=live |archive-url=https://web.archive.org/web/20151114211717/http://www.reuters.com/article/2012/08/28/us-china-walnuts-idUSBRE87R0NV20120828 |archive-date=14 November 2015 |work=Reuters}}</ref> Pairs of walnuts are sometimes sold in their green husks for a form of gambling known as ''du qing pi''.<ref>{{Cite journal |last=Hsieh |first=I-Yi |date=13 May 2016 |title=Asian Anthropology Nuts: Beijing folk art connoisseurship in the age of marketization |url=https://www.academia.edu/25307556 |journal=Asian Anthropology |doi=10.1080/1683478X.2016.1164354 |s2cid=148515450}}</ref>

== Cultivars ==
{{columns-list|colwidth=12em|
* Ashley
* Chandler<ref name="Cultivar">{{Cite web |year=2018 |title=Walnut Cultivar Table |url=http://fruitandnuteducation.ucdavis.edu/fruitnutproduction/Walnut/Walnut_Cultivar_Table/ |url-status=live |archive-url=https://web.archive.org/web/20180208064318/http://fruitandnuteducation.ucdavis.edu/fruitnutproduction/Walnut/Walnut_Cultivar_Table/ |archive-date=8 February 2018 |access-date=6 March 2018 |publisher=Fruit and Nut Information Center, Department of Plant Sciences, University of California, Davis}}</ref>
* Cisco<ref name="Cultivar" />
* Dawson<ref name="Cultivar" />
* Eureka<ref name="Cultivar" />
* Feradam
* Ferbel
* Ferjean
* Fernette<ref name="Cultivar" />
* Fernor
* Ferouette
* Forde<ref name="Cultivar" />
* Franquette<ref name="Cultivar" />
* Grandjean<ref>fr:Le Verger Francais tomme II Chapitre I Fruits Locaux & Regionaux 1948 The French en:Orchard Book II Chapter I Local & Regional Fruits 1948</ref>
* Germisara
* Gillet<ref name="Cultivar" />
* Hansen
* Hartley<ref name="Cultivar" />
* Howard<ref name="Cultivar" />
* Hu
* Ivanhoe<ref>{{cite patent |country=US|number=USPP21718P2|status=active|title=Walnut tree named 'Ivanhoe' (patent) |pubdate=2011-02-22 |gdate=2011-02-22 |fdate=2009-12-08|pridate=2009-12-08 |invent1=Gale McGranahan |invent2=Charles Leslie |assign1=THE REGENTS OF THE UNIVERSITY OF CALIFORNIA |class= |url=http://www.google.com/patents/USPP21718}}</ref>
* Jupanesti
* Lara
* Livermore
* Marbot
* Mayette<ref name="ReferenceA">Le Verger Francais, Tome 1 Catalogue Descriptif des Fruits Adoptes 1947</ref>
* Meylanaise<ref name="ReferenceA" />
* Paradox
* Parisienne
* Payne<ref name="Cultivar" />
* Poe<ref name="Cultivar" />
* Robert Livermore<ref name="Cultivar" />
* Rita
* Ronde de Montignac
* Royal
* Serr<ref name="Cultivar" />
* Sexton<ref name="Cultivar" />
* Solano<ref name="Cultivar" />
* Sunland<ref name="Cultivar" />
* Tehama<ref name="Cultivar" />
* Tulare<ref name="Cultivar" />
* Valcor
* Vina<ref name="Cultivar" />
* Wilson's Wonder
* Yolo
}}

==Gallery==
<gallery mode="packed">
File:Juglans regia 2009 G2.jpg|Common walnut in growth
File:California Blackwalnut.jpg|[[Juglans californica|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:Cerneaux de noix.jpg|Broken walnut meats
File:Gozinaki with walnuts.jpg|[[Georgia (country)|Georgian]] snack [[Gozinaki]] made from roasted walnuts and honey
File:Applesauce walnut coffee cake.jpg|[[Applesauce]] [[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
File:Walnut kernel photographed in West Bengal, India.jpg|Loose Walnut kernel in West Bengal, India.
</gallery>

== References ==
{{reflist}}

== Further reading ==
* {{Cite book |last=Ramos |first=David D. |url=https://books.google.com/books?id=yKawaOt88A0C |title=Walnut Production Manual |publisher=UCANR |year=1997 |isbn=978-1-879906-27-3}}
* {{Cite book |last=Smith |first=Jane S. |title=The Garden of Invention Luther Burbank and the Business of Breeding Plants |publisher=Penguin Books |year=2009 |isbn=978-0-14-311689-9}}

== External links ==
{{Commons category|Walnuts}}
* {{eol|38394}}

{{Nuts}}

[[Category:Crops]]
[[Category:Edible nuts and seeds]]
[[Category:Fruit trees]]
[[Category:Juglans| ]]
[[Category:Plant dyes]]
[[Category:Symbols of California]]

Walnut - Revision history

Ajay Kumar: Created a new article