Hazelnut

The common hazel is a multi-stemmed deciduous shrub or small tree that usually reaches three to eight metres. In late summer it bears nuts in clusters of one to four, each wrapped in a leafy, ruffled husk called an involucre. The nut itself is roughly spherical to slightly oval, about one to two and a half centimetres across, with a smooth, woody, light brown shell and a pale scar at the base. Inside is a single ivory kernel covered by a thin, papery brown skin that tastes slightly bitter and is often rubbed off after roasting. The flavour is sweet, buttery and gently resinous, deepening to a toasty, caramel note when roasted. Hazelnuts are sold in the shell, as blanched or skin-on kernels, whole, chopped, ground into meal or flour, and as paste, butter and pressed oil.

The common hazel is native to Europe and western Asia, ranging from the British Isles and Scandinavia through the Mediterranean to the Caucasus and Anatolia. Hazelnut shells are among the most frequent plant remains found at prehistoric European campsites, which shows that people were gathering the nuts long before farming began. Commercial cultivation grew up around the Black Sea coast of Turkey and in Italy and Spain, and later in Oregon in North America. The genus name Corylus comes from the Greek and Latin words for a hood or helmet, a reference to the husk, while avellana is tied to the Italian town of Avella near Naples, once a famous nut market. The English word hazel descends from Old English haesel, and filbert is traditionally linked to Saint Philibert, whose feast day falls around when the nuts ripen.

Gathered hazelnuts fed hunter-gatherers across northern Europe for thousands of years, and the shrub was valued just as much for its supple stems, which were coppiced to make fences, baskets, hurdles and wattle for house walls. In Celtic and Norse folklore the hazel was a tree of wisdom; Irish tales describe a sacred hazel beside a well whose nuts gave knowledge to whoever ate them. Roman writers praised the nuts of Pontus and Campania, and trade across the Mediterranean carried them widely. By the Middle Ages monastery and manor gardens kept cultivated forms, and cobnuts became a notable crop in the English county of Kent. The great expansion came with the modern confectionery industry. In Piedmont, where cocoa was scarce in the nineteenth century, makers stretched chocolate with ground hazelnuts, a practice that produced gianduja and later spreads sold around the world. Turkey became by far the leading producer, and its Black Sea hillsides still supply most of the global crop. Today hazelnuts are grown on a significant scale in Italy, the United States, Azerbaijan and Chile, and plant breeders are working on varieties resistant to eastern filbert blight.

Hazelnuts are eaten out of hand, toasted to bring out their aroma, and added to cakes, biscuits, tarts, granola and salads. In European pastry they appear as praline, nougat, dacquoise and gianduja, and ground hazelnut meal replaces part of the wheat flour in many gluten-free bakes. Hazelnut paste and spreads are mixed with cocoa, while hazelnut oil is used cold in dressings because heat dulls its flavour. In Spain, romesco sauce is thickened with toasted nuts, and in the Middle East ground hazelnuts flavour desserts and dukkah-style blends. Hazelnut milk is a plant-based drink. Traditional uses of the tree include coppiced wood for hurdles and walking sticks, and the husks and shells serve as fuel or mulch.

Hazelnuts are rich in monounsaturated fat, mainly oleic acid, and provide vitamin E, manganese, copper and some magnesium, along with fibre and plant sterols. Studies on regular nut consumption generally link it with modestly better blood lipid profiles and lower cardiovascular risk in observational research, although results for individual nut types vary and nuts are energy dense. Hazelnuts also contain polyphenols concentrated mostly in the skin. They are a useful source of healthy fat in vegetarian eating patterns, but they are not a treatment for any condition, and a small handful a day is the portion most often used in studies.