The chestnut belongs to the same Fagaceae family as the oak and beech. There are four main species, commonly known as European, Chinese, Japanese and American chestnuts:
European species sweet chestnut (Castanea sativa) (also called "Spanish chestnut" in the US) is the only European species of chestnut, though successfully introduced to the Himalayas and other temperate parts of Asia.
Asiatic species Castanea crenata (Japanese chestnut), Castanea mollissima (Chinese chestnut), Castanea davidii (China), Castanea henryi (Chinese chinkapin, also called Henry's chestnut – China) and Castanea seguinii (also called Seguin's chestnut - China).
American species These include Castanea dentata (American chestnut - Eastern states), Castanea pumila (American- or Allegheny chinkapin, also known as "dwarf chestnut" - Eastern states), Castanea alnifolia (Southern states), Castanea ashei (Southern states), Castanea floridana (Southern states) and Castanea paupispina (Southern states).
Chestnuts should not be confused with horse chestnuts (genus Aesculus), which are unrelated to Castanea and are named for producing nuts of similar appearance but of no notable edibility. Nor should they be confused with water chestnut (family Cyperaceae), which are also unrelated to Castanea and are tubers of similar taste from an aquatic herbaceous plant. Other trees commonly mistaken for the chestnut tree are the chestnut oak (Quercus prinus) and the American beech (Fagus grandifolia).
Chestnut trees are of moderate growth rate (for the Chinese chestnut tree) to fast-growing for American and European species. Their mature heights vary from the smallest species of chinkapins, often shrubby, to the giant of past American forests, Castanea dentata that could reach 60 m. In between these extremes are found the Japanese chestnut (Castanea crenata) at 10 m average; followed by the Chinese Chestnut (Castanea mollissima) at about 15 m, then the European chestnut (Castanea sativa) around 30 m.
The Chinese and more so the Japanese chestnuts are both often multileadered and wide-spreading, whereas European and especially American species tend to grow very erect when planted among others, with little tapering of their columnar trunk, which is firmly set and massive. When standing on their own, they spread on the sides and develop broad, rounded, dense crowns at maturity. The two latter's foliage has striking yellow autumn coloring.
Its bark is smooth when young, of a vinous maroon or red-brown color for the American chestnut, grey for the European chestnut. With age American species' becomes grey and darker, thick and deeply furrowed; the furrows run longitudinally, and tend to twist around the trunk as the tree ages; it sometimes reminds one of a large cable with twisted strands.
The leaves are simple, ovate or lanceolate, 10–30 cm long and 4–10 cm wide, with sharply pointed, widely-spaced teeth, with shallow rounded sinuates between.
The flowers follow the leaves, appearing in late spring or early summer or onto July. They are arranged in long catkins of two kinds, with both kinds being borne on every tree. Some catkins are made of only male flowers, which mature first. Each flower has eight stamens, or 10 to 12 for Castanea mollissima. The ripe pollen carries a heavy sweet odor that some people find too sweet or unpleasant. Other catkins have these pollen-bearing flowers, but also carry near the twig from which these spring, small clusters of female or fruit-producing flowers. Two or three flowers together form a four-lobed prickly calybium, which ultimately grows completely together to make the brown hull, or husk, covering the fruits.
The fruit is contained in a spiny (very sharp) cupule 5–11 cm in diameter, also called "bur" or "burr". The burrs are often paired or clustered on the branch and contain one to seven nuts according to the different species, varieties and cultivars. Around the time the fruits reach maturity, the burrs turn yellow-brown and split open in 2 or 4 sections. They can remain on the tree longer than they hold the fruit, but more often achieve complete opening and release the fruits only after having fallen on the ground; opening is partly due to soil humidity.
The chestnut fruit has a pointed end with a small tuft at its tip (called "flame" in Italian, and at the other end, a hilum – a pale brown attachment scar. In many varieties, the fruit is flattened on one or two sides. It has two skins. The first one is a hard outer shiny brown hull or husk, called the pericarpus; the industry calls this the peel. Underneath the pericarpus is another thinner skin, called the "pellicle" or "episperm". The pellicle closely adheres to the seed itself, following the grooves usually present at the surface of the fruit. These grooves are of variable sizes and depth according to the species and variety.
The fruit inside these shows two cotyledons with a creamy-white flesh throughout, except in some varieties which show only one cotyledon, and whose episperm is only slightly or not intruded at all. Usually these varieties have only one large fruit per burr, well rounded (no flat face) and which is called "marron" ("marron de Lyon" in France, "marron di Mugello" in Italy, or "Paragon").
The superior fruiting varieties among European chestnuts have good size, sweet taste and easy-to-remove inner skins. American chestnuts are usually very small (around 5 g), but sweet-tasting with easy-to-remove pellicles. Some Japanese varieties have very large nuts (around 40 g), with typically difficult-to-remove pellicles. Chinese chestnut pellicles are usually easy to remove, and their sizes vary greatly according to the varieties, although usually smaller than the Japanese chestnut.
Fresh chestnut fruits have about 180 calories (800 kJ) per 100 grams of edible parts, which is much lower than walnuts, almonds, other nuts and dried fruit (about 600 kcal/100 g). Chestnuts, as with all plant foods, contain no cholesterol[49] and contain very little fat, mostly unsaturated, and no gluten.
Their carbohydrate content compares with that of wheat and rice; chestnuts have twice as much starch as the potato. In addition, chestnuts contain about 8 percent of various sugars, mainly sucrose, glucose, fructose, and, in less amount, stachyose, and raffinose. In some areas, sweet chestnut trees are called "the bread tree". When chestnuts are just starting to ripen, the fruit is mostly starch and is very firm under finger pressure from the high water content. As the chestnuts ripen, the starch is slowly converted into sugars; and moisture content also starts decreasing. Upon pressing the chestnut, a slight 'give' can be felt; the hull is not so tense, and there is space between it and the flesh of the fruit. The water is being replaced by sugars, which means better conservation.
They are the only "nuts" that contain vitamin C, with about 40 mg per 100 g of raw product, which is about 65 percent of the U.S. recommended daily intake. The amount of vitamin C decreases by about 40 percent after heating. Fresh chestnuts contain about 52 percent water by weight, which will evaporate relatively quickly during storage; they can lose even 1 percent of weight in one day at 20 °C and 70% relative humidity.
Tannin is contained in the bark as well as in the wood, leaves and seed husks. The husks contain 10–13% tannin.
The fruit can be peeled and eaten raw, but it can be somewhat astringent, especially if the pellicle is not removed.
Another method of eating the fruit involves roasting, which does not require peeling. Roasting requires scoring the fruit beforehand to prevent undue expansion and "explosion" of the fruit. Once cooked, its texture is similar to that of a baked potato, with a delicate, sweet, and nutty flavour. This method of preparation is popular in northern China as well as in Portugal, Spain, Turkey, Greece, Italy, France, Korea and Southeast Asia, where the scored chestnuts may be cooked in a tub of heated coal pebbles[clarification needed] mixed with a little sugar.
Chestnuts can be dried and milled into flour, which can then be used to prepare breads, cakes, pancakes, pastas (it is the original ingredient for polenta, known in Corsica as pulenda), or used as thickener for stews, soups, and sauces. In Corsica, the flour is fried into doughnut-like fritters called fritelli and made into necci, pattoni, castagnacci, and cialdi.
The flour can be light beige like that from Castagniccia, or darker in other regions. It is a good solution for long storage of a nutritious food. Chestnut bread can stay fresh for as long as two weeks.
The nuts can also be eaten candied, boiled, steamed, grilled, or roasted in sweet or savoury recipes. They can be used to stuff vegetables, poultry, fowl and other edibles. They are available fresh, dried, ground or canned (whole or in puree).
A fine granular sugar can be obtained from the fermentation of the juice, as well as a beer; the roasted fruit provides a coffee substitute. Parmentier, who among other things was a famous potato promoter, extracted sugar from chestnuts and sent a chestnut sugarloaf weighing several pounds to the Academy of Lyon. The continental blockade following shortly after (1806–1814) increased the research into developing chestnuts as a source of sugar, but Napoleon chose beets instead.
Candied chestnuts (whole chestnuts candied in sugar syrup, then iced are sold under the French name marrons glacés or Turkish name kestane şekeri ("sugared chestnuts"). They appeared in France in the 16th century. Towards the end of 19th century, Lyon went into a recession with the collapse of the textile market, notably silk. Clément Faugier ingénieur des Ponts et Chaussées was looking for a way to revitalize the regional economy. In 1882 at Privas, he invented the technology to make marrons glacés on an industrial scale (although a great deal of the over-twenty necessary steps from harvest to the finished product are still accomplished manually). Chestnuts are picked in autumn, and candied from the start of the following summer for the ensuing Christmas. Thus the marrons glacés eaten at Christmas are those picked the year before.
Sweet chestnuts are not easy to peel when cold. One kilogram of untainted chestnuts yields about 700 g of shelled chestnuts.
Chestnut flavors vary slightly from one to the next, but it[clarification needed]is somewhat sweet and certainly unique. Chestnut-based recipes and preparations are making a comeback in Italian cuisine, as part of the trend toward rediscovery of traditional dishes and better nutrition.
Chestnut wood is a useful source of natural tannin and was used for tanning leather before the introduction of synthetic tannins. On a 10% moisture basis, the bark contains 6.8% tannin and the wood 13.4%.[53] The bark imparts a dark colour to the tannin, and has a higher sugar content, which increases the percentage of soluble non-tans, or impurities, in the extract; so it was not employed in this use.
Chestnut tannin has a naturally low pH value, relatively low salts content and a high acids content. It is one of the pyrogallol class of tannins (also known as hydrolysable tannin). As it tends to give a reddish tone to the leather, it is most often used in combination with quebracho, mimosa, myrabolans, and valonia.
The wood seems to reach its highest tannin content after the trees reach 30 years old. The southern European chestnut wood usually contains at least 10 to 13% more tannin than chestnut trees in northern climates. Today, the largest producer of extract for tanning is Italy.
Fabric can be starched with chestnut meal.
Linen cloth can be whitened with chestnut meal.
The leaves and the skins (husk and pellicle) of the fruits provide a hair shampoo.
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