Chestnut

The sweet chestnut is a large, long-lived deciduous tree that can grow to thirty metres, with long toothed leaves and catkins of creamy flowers in summer. The nuts ripen in autumn inside spiny green husks called burs, each holding one to three glossy, reddish-brown nuts with a pale, leathery inner skin.

Unlike most nuts, chestnuts are low in fat and high in starch, giving a soft, sweet, floury texture when cooked. They are sold fresh in autumn, dried, peeled and vacuum-packed, canned as a purée, candied as marrons glaces and ground into flour. Cultivars with a single large nut are known as marrons in France and Italy.

The sweet chestnut is native to southern Europe and Asia Minor, with natural stands in the Caucasus, Turkey, Greece, Italy and the Iberian Peninsula. The Romans and earlier Greeks cultivated it widely and carried it across their empire, including to Britain.

The English name comes from Old French chastaigne, via Latin castanea, from the Greek kastanea, which may relate to the town of Kastana in Asia Minor. The tree is not related to the horse chestnut, Aesculus hippocastanum, whose seeds resemble chestnuts but are toxic.

Chestnuts were a staple in the mountainous regions of Mediterranean Europe, where grain was difficult to grow. In the Apennines, Corsica, the Cevennes and northern Spain, families lived on chestnut flour, which was made into breads, porridges and polenta, giving the tree its title of the bread tree. Nuts were dried in smoky drying houses and stored through winter.

Romans introduced improved varieties and grafting, and medieval monasteries expanded chestnut orchards. By the nineteenth century, migration, the decline of mountain villages and the availability of potatoes and maize reduced dependence on chestnuts.

A further blow came from chestnut blight, caused by the fungus Cryphonectria parasitica, which was accidentally introduced to North America from Asia around 1900 and killed billions of American chestnut trees, formerly a dominant forest species. European trees were also affected, though less severely. Breeding and conservation programmes, including crosses with blight-resistant Asian chestnuts, aim to restore the tree. Today Turkey, China, Italy, South Korea and Spain are among the biggest producers, and roast chestnuts remain a popular street food in autumn.

Chestnuts are roasted over fire, boiled, steamed or braised, and used in stuffings, soups, stews and roast vegetable dishes. Pureed chestnut makes the French dessert Mont Blanc, and candied chestnuts are a classic holiday sweet. Chestnut flour is used in Italian breads, pancakes (necci), polenta and cakes, and it is naturally gluten free.

Chestnut honey, dark and slightly bitter, is a regional product. Before cooking, a cut is scored in the shell to stop the nut bursting. In East Asia, Chinese and Japanese chestnuts are roasted and used in rice dishes and sweets. The wood is valued for fencing and furniture.

Chestnuts are unusual among nuts for being low in fat and high in complex carbohydrate, and they provide vitamin C, potassium, copper and some B vitamins. They contribute fibre and are gluten free, which makes chestnut flour useful for people avoiding wheat.

Their starch content means they raise blood sugar more than fatty nuts such as almonds, so portion size matters for people monitoring carbohydrates. Chestnuts are best viewed as a nutritious, seasonal starchy food and not as a health remedy.