Walnut

Awalnutis the edibleseedof any tree of the genusJuglans(familyJuglandaceae), particularly the Persian or English walnut,Juglans regia. They areaccessory fruitbecause the outer covering of the fruit is technically aninvolucreand thus not morphologically part of the carpel; this means it cannot be adrupebut is instead a drupe-like nut.
After full ripening, theshellis discarded, and the kernel is eaten. Nuts of the eastern black walnut (Juglans nigra) and butternuts (Juglans cinerea) are less commonly consumed.
Walnuts are the round, single-seedstone fruitsof the walnut tree. They ripen between September and November in the northern hemisphere. The brown, wrinkly walnut shell is enclosed in ahusk.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.The seed kernels – commonly available as shelled walnuts – are enclosed in a brownseed coatwhich contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen, preventingrancidity.
Walnut trees are late to growleaves, typically not doing so until more than halfway through the spring.
Walnut hulls contain diversephytochemicals, such aspolyphenols, that stain hands and can cause skin irritation. Seven phenolic compounds, includingferulic acid,vanillic acid,coumaric acid,syringic acid,myricetin, andjuglone, 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 acidandsitosterolfrom the stem bark ofJ. regia.
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 includeJ. californica, the California black walnut (often used as arootstockfor commercial propagation ofJ. regia),J. cinerea(butternuts), andJ. major, the Arizona walnut. Other sources listJ. californica californicaas native to southern California, andJuglans californica hindsii, or justJ. hindsii, as native to northern California; in at least one case, these are given as "geographic variants" instead of subspecies (Botanica).
Numerous walnutcultivarshave been developed commercially, which are nearly all hybrids of the English walnut.
During theByzantine era, the walnut was also known by the name "royal nut".An article on walnut tree cultivation in Spain is included inIbn al-'Awwam's 12th-centuryBook on Agriculture.Thewalelement in the name is Germanic and meansforeign, especially in the sense ofLatinornon-Germanic. Compare, for example,Wales,Walloons,Wallachia. Thewalelement is present in other Germanic-language words for the same nut, such as: GermanWalnuss, Dutchwalnoot, Danishvalnød, and Swedishvalnöt.
Walnuts, like other tree nuts, must be processed and stored properly. Poor storage makes walnuts susceptible to insect and fungal mold infestations; the latter producesaflatoxin– a potentcarcinogen. A batch that contains mold-infested walnuts should be entirely discarded.
The ideal temperature for the extended storage of walnuts is −3 to 0 °C (27 to 32 °F) 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 25 °C (77 °F) with low humidity. Temperatures above 30 °C (86 °F) 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.
In 2022, world production of walnuts (in shell) was 3.9 milliontonnes, with China contributing 36% of the total (table). Other significant producers (in the order of decreasing harvest) were the United States,Iran, andTurkey.
English walnuts without shells are 4% water, 15%protein, 65% fat, and 14%carbohydrates, including 7%dietary fiber(table). In a reference amount of 100 g (3.5 oz), walnuts provide 654 kilocalories (2,740 kJ) and rich contents (20% or more of theDaily Value, DV) of severaldietary minerals, particularlymanganeseat 148% DV, along with significant amounts ofB vitamins(table).
Unlike most nuts, which are high inmonounsaturated fatty acids,walnut oilis composed largely ofpolyunsaturated fatty acids(72% of total fats), particularlyalpha-linolenic acid(14%) andlinoleic acid(58%), although it does containoleic acidas 13% of total fats (table source).
In 2004, the USFood and Drug Administration(FDA) provided a qualifiedhealth claimallowing products containing walnuts to state: "Supportive but not conclusive research shows that eating 1.5 ounces (43 g) per day of walnuts, as part of a lowsaturated fatand lowcholesteroldiet and not resulting in increased caloric intake, may reduce the risk ofcoronary 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 awarning lettertoDiamond Foodsstating there is "not sufficient evidence to identify abiologically active substancein walnuts that reduces the risk of coronary heart disease."
In 2011, a scientific panel for theEuropean Food Safety Authorityrecommended a health claim that "Walnuts contribute to the improvement ofendothelium-dependentvasodilation" at a daily intake of 30 grams (1.1 oz); it also found that acause and effect relationshipdid not exist between consuming walnuts and reduction of bloodLDL-cholesterollevels.The recommended health claim was later authorized by theEuropean Commission.
A 2020systematic reviewassessing the effect of walnutsupplementationonblood pressurefound insufficient evidence to support walnut consumption as a blood pressure-lowering strategy.
As of 2021, the relationship between walnut consumption andcognitive healthis inconclusive.
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 asmuesli, or as an ingredient of adish: 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 inbaklava,Circassian chicken,potica(a traditional festive pastry fromSlovenia),satsivi(chicken in walnut sauce),tarator(a summer soup inBulgarian cuisine), andpoultry or meat ballstewfromIranian cuisine.
Walnuts are also popular as anice creamtopping, and walnut pieces are used as agarnishon some foods.
Nocinois aliqueurmade from unripe green walnuts steeped inalcoholwith syrup added.
Walnut oilis available commercially and is chiefly used as a food ingredient, particularly insalad dressings. It has a lowsmoke point, which limits its use forfrying.
Walnut husks can be used to make durable ink for writing and drawing. It is thought to have been used by artists includingLeonardo da VinciandRembrandt.
Walnut husk pigments are used as a browndyefor fabricand were used inclassical Romeandmedieval Europefordyeing hair.
TheUS Armyonce used ground walnut shells forabrasive blastingto clean aviation parts because of low cost and low abrasive qualities. However, an investigation of a fatalBoeing CH-47 Chinookhelicopter 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 filtersof ground walnut shell are used for "polishing" (filtering) oily contaminates from water.
At least two companies, LitterMaid and Naturally Fresh, makecat litterfrom 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.
Walnuts have been listed as one of the 38 substances used to prepareBach flower remedies,aherbal remedypromoted infolk medicine practicesfor its supposed effect on health. According toCancer Research UK, "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer".
Large, symmetrically shaped, and sometimes intricately carved walnut shells (mainly fromJ. hopeiensis) are valued collectibles in China where they are rotated in hand as a plaything or as decoration. They are also an investment andstatus symbol, with some carvings having highmonetary valueif unique.Pairs of walnuts are sometimes sold in their green husks for a form of gambling known asdu qing pi.