The hazelnut is the fruit of the hazel tree and therefore includes any of the nuts deriving from species of the genus Corylus, especially the nuts of the species Corylus avellana. They are also known as cobnuts or filberts according to species.
Hazelnuts are used as a snack food, in baking and desserts, breakfast cereals such as muesli, confectionery to make praline, and also used in combination with chocolate for chocolate truffles and products such as chocolate bars, hazelnut cocoa spread such as Nutella, and Frangelico liqueur. Hazelnut oil, pressed from hazelnuts, is strongly flavored and high in monounsaturated fat; it is used as a cooking oil and as a salad or vegetable dressing. Turkey is the world's largest producer of hazelnuts, accounting for 64% of total production in 2021.
A hazelnut cob is roughly spherical to oval, about long and in diameter, with an outer fibrous husk surrounding a smooth shell, while a filbert is more elongated, being about twice as long as its diameter. The nut falls out of the husk when ripe, about seven to eight months after pollination. The seed is edible and consumed raw, roasted or ground into a paste. The seed has a thin, dark brown skin, which is sometimes removed before cooking.
In 1995, evidence of large-scale Mesolithic nut processing, some 8,000 years old, was found in a midden pit on the island of Colonsay in Scotland. The evidence consists of a large, shallow pit full of the remains of hundreds of thousands of burned hazelnut shells. Hazelnuts have been found on other Mesolithic sites, but rarely in such quantities or concentrated in one pit. The nuts were radiocarbon dated to 7720±110 BP, which calibrates to 6000 BCE. Similar sites in Britain are known only at Farnham in Surrey and Cass ny Hawin on the Isle of Man.
This discovery gives an insight into communal activity and planning in the period. The nuts were harvested in a single year, and pollen analysis suggests that all of the hazel trees were cut down at the same time.