The Sweet Chestnut (Castanea sativa, family Fagaceae), also known as the Spanish Chestnut, Portuguese Chestnut or European chestnut, is a species of chestnut originally native to southeastern Europe and Asia Minor.
It is a medium-sized to large deciduous tree attaining a height of 20-35 m with a trunk often 2 m in diameter. The oblong-lanceolate, boldly toothed leaves are 16-28 cm long and 5-9 cm broad.
The flowers of both sexes are borne in 10-20 cm long, upright catkins, the male flowers in the upper part and female flowers in the lower part. They appear in late June to July, and by autumn, the female flowers develop into spiny cupules containing 3-7 brownish nuts that are shed during October. Some species ("Marron de Lyon, Paragon' and some hybrids) produce only 1 large nut, rather than the average 2 to 4 nuts of edible size.
The bark often has a net-shaped (retiform) pattern with deep furrows or fissures running spirally in both directions up the trunk.
The tree requires a mild climate and adequate moisture for good growth and a good nut harvest. Its year-growth (but not the rest of the tree) is sensitive to late spring and early autumn frosts, and is intolerant of lime. Under forest conditions it will tolerate moderate shade well.
Sweet Chestnut is widely cultivated for its edible seeds, also called nuts. As early as Roman times it was introduced into more northerly regions, and later was also cultivated in monastery gardens by monks. Today, centuries-old specimens may be found in Great Britain and the whole of central, western and southern Europe. They are widely popular in Turkey, Portugal, France, Hungary, Italy, Croatia, Bosnia and particularly in Corsica.
The raw nuts, with their pithy skin around the seed, are somewhat astringent. That skin can be relatively easily removed by quickly blanching the nuts after having made a cross slit at the tufted end. Once cooked they become delicious, developing, when roasted, a sweet flavour and floury texture not unlike sweet potato. The cooked nuts can be used by confectioners, puddings, desserts and cakes or eaten roasted. They are used for flour, bread making, a cereal substitute, coffee substitute, a thickener in soups and other cookery uses, as well as for fattening stock. A sugar can be extracted from it. The Corsican variety of polenta (called pulenta) is made with sweet chestnut flour. A local variety of Corsican beer also uses chestnuts. An easy way for peeling them is given here.
Leaves infusions are used in respiratory diseases and are a popular remedy for whooping cough. It is much used in homeopathy and in Bach remedies for depression which the key words are 'Extreme mental anguish', 'Hopelessness' and 'Despair'. A hair shampoo can be made from ifusing leaves and fruit husks.
This tree responds very well to coppicing, which was practiced until recently in Britain, and produces a good crop of tannin-rich wood every ten years or so. The tannin renders the young growing wood durable and resistant to outdoor use, thus suitable for posts, fencing or stakes. The wood is of light colour, hard and strong. It is also used to make furniture, barrels (sometimes used to age balsamic vinegar), and roof beams notably in southern Europe (for example in houses of the Alpujarra, Spain, in southern France and elsewhere). Due to older wood's tendency to split and warp badly, and acquiring a certain brittleness, it is not frequently used in large pieces. It is also a good fuel.
Tannin is found in the following proportions on a 10% moisture basis: bark (6.8%), wood (13.4%), seed husks (10 - 13%). The leaves also contain tannin.
A tree grown from seed may take twenty years or more before it bears fruits, but a grafted species such as "Marron de Lyon" or "Paragon" may start production within five years of being planted. Both the latter species bear fruits with a single large kernel, rather than an average of two to four smaller kernels.