Walnut

The common walnut tree grows up to 25 metres tall with a broad crown and aromatic compound leaves. Its fruit is a round green husk that dries and splits, releasing a hard, wrinkled, tan shell around the edible kernel. The kernel divides into two lobed halves joined at the centre, and is covered by a thin papery skin that can taste slightly bitter and astringent. The flavour is rich, buttery and slightly tannic. Walnuts are sold in the shell, as halves and pieces, blanched or roasted, and as cold-pressed oil.

Juglans regia is believed to be native from southeastern Europe through Central Asia to the Himalayas and western China, with forests of wild walnuts surviving in Kyrgyzstan, Uzbekistan and neighbouring regions. Humans carried it west and east in antiquity. It is now grown in temperate climates around the world. China is the largest producer by a wide margin, followed by the United States, where California grows nearly all commercial walnuts, and countries such as Iran, Turkey and Ukraine. The tree needs cold winters and deep soils.

Walnut remains have been found at prehistoric sites in Europe and Asia, and the nut was widely traded in the ancient world. The Romans knew it as Jovis glans, the acorn of Jupiter, which became the botanical name Juglans. The English word walnut comes from Old English wealhhnutu, meaning foreign nut, because it came to Britain from the Roman world. The tree also supplied dye and medicinal materials, and its dark timber has been prized for furniture, gunstocks and veneer for centuries.

Walnuts spread to the Americas with Spanish missionaries, who planted them in California in the eighteenth century, and commercial orchards grew from the nineteenth century, with improved varieties such as Hartley and Chandler. In Europe the nuts became a pantry staple in regions from France to Georgia, where they are the basis of sauces such as satsivi. Pickled green walnuts, walnut liqueur and walnut oil are traditional products in several regions, and the nuts have become widely associated with heart-healthy eating in modern nutrition guidance.

Walnuts are eaten raw as snacks and used in baking, including brownies, banana bread and baklava, and in salads, pestos, grain dishes and cheese plates. They are ground into sauces, such as Georgian bazhe and Spanish and Italian walnut sauces, and into vegetarian meat alternatives. Walnut oil is used for dressings and finishing, but not for high-heat cooking. Ground shells serve as abrasives, and husks have been used as a natural dye.

Walnuts are notable among tree nuts for their polyunsaturated fat, including roughly 2.5 grams of alpha-linolenic acid per ounce, a plant omega-3 fatty acid. They also provide copper, manganese, magnesium and phosphorus, along with polyphenols concentrated in the papery skin. Regular nut consumption, including walnuts, has been associated in observational studies and some trials with improvements in blood cholesterol. They are energy dense, so a small handful is a sensible portion. Rancid nuts taste bitter and are best discarded.