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Acorn (Oak nut) is the nut from the oaks and other species in genera Quercus (oaks) and Lithocarpus (beech), in the family Fagaceae. Quercus contains about 400 species, and Lithocaepus has about 334 species. The acorn is a cup-shaped cupule, containing a single seed enclosed in a tough and leathery shell. The cupule partly encloses and protects the seed, during the growth and maturation period which takes about 6-24 months, depending on species. It comes in various sizes, from 1-6 cm long and 0.8-4 cm broad.
Acorn is an important wildlife food source for birds such as jays, pigeons, some ducks and several species of woodpeckers. Mice, squirrels and several other rodents are small mammals that feed on acorns. Other large mammals that feed on acorns are pigs, bears and deers, and it may constitute up to 25% of a deer's diet in autumn. In southwest Europe such as Spain and Potugal, pigs are let loose in dehasas (wooded pastureland) in autumn, to fill and fatten themselves on acorns. However, acorn is toxic to some animals, such as horses. Larvae of some species of moths and weevils live in young acorns, feeding on the kernels as they develop.
Acorns contain large amount of protein, carbohydrates, fats, and minerals such as calcium, phosphorus and potassium, and vitamin niacin. The percentages of each nutrient is varied from species to species, but are compared well with other wild foods and nuts. Acorns also contain tannin, a plant polyphenols which interfere with an animal's ability to metabolize protein, so the animal must adapts in different ways to utilize the nutritional value that acorns contain. Jays and squirrels may wait to consume the acorns until sufficient groundwater has percolated (movement and filtering of fluids through porous material) through the nuts to leach out the tannins, while some animals buffer the acorn diet with other food.
Many acorn eaters consume unripe acorns on the tree or ripe acorns from the ground, with no reproductive benefit to the oak. However some are seed dispersal agents, such as jays and squirrels which scatter-hoard acorns in caches for future use. This method effectively plant acorns in a variety of locations, in which it is possible for the acorns to germinate and thrive. Although jays and squirrels retain remarkably large mental maps on cache locations and return to eat them, some odd acorns may be lost , or a jay or squirrel may die before consuming all the stored acorns, resulting in a small numbers manage to germinate and survive, producing the next generation of oaks.
Acorns appear only on adult trees and thus is often referred to as a symbol of patience and the fruition of long, hard labor. Acorn jelly or dotorimuk is a Korean food made from acorn starch, a practice originated in the mountainous areas of ancient Korea. Dotorimuk is often eaten in the form of dotorimuk muchim, a side dish in which small chunks of dotorimuk are seasoned and mixed with other ingredients such as red chili pepper powder, sesame seeds, sesame oils, slivered carrots, scallions, soy sauce and garlic. Tannins can be removed by soaking chooped acorns in several changes of water, until the water no long turns brown. Boiling may caused the tannins to be unleachable. Acorn flour can spoil or get moldy easily due to high fat content, and must be stored carefully.