The use of wild mushrooms as a food is an ancient practice. These fungi were undoubtedly well known to pre-historic, hunting and gathering cultures, as they are today to indigenous peoples who continue to live in natural forests. Once the identity of poisonous and edible mushrooms became fixed in cultural knowledge and tradition, the edible species, and sometimes those that could be used to induce non-lethal hallucinogens, were regularly gathered and utilized by people.
The tradition of the use of mushrooms as a country food continues today. The collection of edible mushrooms is an especially popular outdoor activity in much of Eurasia, where these foods can be very common in the spring and autumn in boreal and temperate forests. Mushroom collecting has been considerably less popular in Britain and North America. However, under the influence of immigrants from Europe and northern Asia, and the emerging popularity of natural history, more and more North Americans are actively seeking out these delicacies in wild habitats. This activity has been called "mushrooming," in parallel with the better-known sport of "birding." Interestingly, most mushrooms are not a particularly nutritious food. They typically contain 90-95% water when fresh, the rest of their biomass being about 5% carbohydrate, 5% protein, and less-than 1% fat and minerals. The major benefit of eating mushrooms is their engaging, sometimes exquisite flavor, and in some cases their interesting texture.
The truffles are perhaps the most famous, and certainly the most expensive, of the edible mushrooms, being avidly sought-out for use in gourmet cooking, particularly in France. The best-known species of truffle is Tuber melanosporum, which is commonly mycorrhizal on species of oak, birch, and beech (Quercus, Betula, and Fagus spp., respectively). Other Eurasian species of truffle include Tuber aestivum and T. brumale, while T. gibbosum occurs in conifer rainforests of the west coast of North America. The spore-bearing mushrooms of truffles develop underground, and are commonly discovered using a specially trained, truffle-sniffing pig or dog.
The chanterelle (Cantharellus cibarius) is a yellow-to-orange mushroom of the floor of autumn forests, and is a delicious wild fungus. The king bolete (Boletus edulis) is another prized mushroom. The shaggy mane (Coprinus comatus) is delicious if picked when young. Puffballs can also be eaten, as long as their interior is still young and white-colored, and include the pear puffball (Lycoperdon pyriforme) and giant puffball (Calvatia gigantea). Other edible mushrooms include corn smut (Ustilago maydis), beefsteak (Fistulina hepatica), fried chicken mushroom (Lyophyllum decastes), fairy ring mushroom (Marasmius oreades), oyster fungus (Pleurotus ostreatus), and the morel (Morchella esculenta).
Some species of mushrooms have been brought into domestication, and are routinely grown on artificial media, to be harvested and sold as an agricultural product. Mushroom cultivation appears to have begun in England in the late eighteenth century, and it has become a major economic enterprise because of the rapidly increasing popularity of mushrooms as food.
The most commonly cultivated species of mushroom is the common meadow mushroom (Agaricus campestris; sometimes known as A. bisporus), which sustains a global economy exceeding $15 billion per year. This mushroom can be eaten fresh or dried for longer-term storage. This species is cultivated using an organic-rich medium, with the straw- and manure-rich cleanings of horse stables being a preferred material. The substrate must be sterilized, usually by a natural, high-temperature composting referred to as "sweating-out." This must be done before the substrate is inoculated with the Agaricus, to prevent the growth of other species of fungus, which may be pathogenic or more competitive than the desired species. The substrate is typically inoculated with "spawn," that is, masses of mycelium compressed into small briquettes, or with a laboratory culture of the Agaricus. The growth conditions should be dark or virtually so, as humid as possible, and the temperature kept constant at about 55–59°F (13–15°C). Mushroom farms may be developed in specially constructed, barn-like buildings, or in caves, worked-out mines, and cellars. Typically, the first mushroom "buttons" begin to appear about four weeks after inoculation and growth and proliferation of the Agaricus mycelium, and the first harvests can be made after 7-8 weeks. The mushrooms can be continuously harvested for 4-6 months, after which the growth medium is considered to be "spent." However, this well-composted substrate can then be used as an excellent soil conditioner in gardens.
Other species of mushrooms are also cultivated, including the shiitake (Cortinellus berkeleyanus), a popular ingredient in oriental cooking. The shiitake mushroom is cultivated on rotting logs and is typically dried for storage.
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