Fungi

WARNING: Collecting and ingesting wild mushrooms without the presence of an expert to correctly identify specimens can be very dangerous and should be discouraged since there are several deadly mushrooms that look like edible wild ones.

Mushroom Collecting

The consumption of wild mushrooms has a lengthy history, dating back well over two millennia and extending throughout the world. For over two hundred years, mushrooms have been a cultivated crop as well. Despite somewhat negative images of mushrooms in the popular imagination and despite the possibility of real danger in their consumption, they have long been valued for their culinary and psychedelic properties. In 300 BC Theophrastus recorded that mushrooms were valued as food and for trade. Pliny, Juvenal, Martial, and Cicero all considered mushrooms to be great delicacies, and the Roman emperor Claudius was allegedly poisoned by a plate of mushrooms. Mushrooms are also mentioned in the Hindu Rig Veda and were eaten on the Indian subcontinent. Mushrooms were probably consumed for food and for their psychedelic properties in Mesoamerica, Siberia, and Scandinavia. Some suggest that the biblical "manna from heaven" was a fungus. By the eighteenth-century reign of Louis XIV, mushrooms were cultivated in caves near Paris. During the nineteenth century mushrooming became a popular leisure pursuit in Europe and America, and by the end of the century mushroom societies were formed.

One estimate placed the number of mushroomers in the United States at thirty million in the early 1980s. A survey conducted at the same time found that 22 percent of Americans collect wild mushrooms, and 15 percent consume mushrooms they find. In the nations of eastern, central, and southern Europe with stronger mushroom cultures, these figures would likely be higher. Mushroom societies are found in every region of the United States, as well as Canada and Europe. In the United States, mushroom societies were founded in Boston and Minneapolis in the late nineteenth century. The North American Mycological Association, covering the United States and Canada, has approximately 2,000 members. These clubs organize talks, dinners, sharing of advice, and forays to mushroom collecting sites.

Novices worry about the toxic qualities of wild mushrooms. Despite this, the number of mushroom fatalities, at least in the United States, is very low. In some years, there are no fatalities although illnesses or hospitalizations might occur as a result of the misidentification of mushrooms, the contamination of otherwise edible specimens, or allergic reactions. Among the edible wild mushrooms that are most widely collected in the United States and Europe are morels, chanterelles, puffballs, boletes, and coral mushrooms. While the collection of wild mushrooms has increased in the past decades, the hobby is limited, and the greatest growth in "wild mushrooms" is likely to occur when these foods become cultivated and therefore perceived as safe to consume.

Fungi vs. Mushrooms

The cultivation of edible mushrooms worldwide reached 6.16 million metric tons in 1997. Six mushroom genera accounted for 87% of the total mushroom supply. China produces 63.6% of the total world output.

What is a mushroom? Mushrooms are the fruiting bodies produced by some fungi. Not all fruit bodies are true mushrooms. Puffballs and morels are edible fruit bodies that are sometimes called "mushrooms." The function of this visible part of some fungi is to produce and disperse the largest possible number of spores in the shortest possible time. Spores create new individuals after being carried away on the wind and landing in a good place for growth.

Puffballs are relatives of mushrooms. Despite producing large mushroom-like fruiting bodies, morels and false morels are not closely related to mushrooms. Their spores are produced inside a special cell and are explosively discharged into the air as a fine white cloud.

In many developing countries, the collection and sale of wild edible mushrooms has become an important source of income for many people in remote forested regions. Despite a relatively short growing season, wild mushrooms provide many families with 50 to 100 percent of their income. World trade in wild, edible mushrooms is estimated at more than $7 billion annually. The global trade in matsutake (Tricholoma matsutake), the most expensive wild mushrooms after truffles, is estimated at $3 to $5 billion. Matsutake may sell for as much as $200 apiece in Tokyo markets.

The King Bolete (Boletus edulis; also known as porcini, cepe, borovik, etc.) is the most popular wild mushroom of Europe. These may be served fresh in some upscale restaurants. Dried boletes are famous for their concentrated flavor and choice aroma and are available year-round from almost anywhere in the world. Other wild mushrooms available on world markets include chanterelles (Cantharellus cibarius), morels (Morchella spp.), hedgehog mushrooms (Hydnum repandum), lobster mushrooms (Hypomyceslactifluorum), candy caps (Lactarius fragilis), and cauliflower mushrooms (Sparassis crispa).

Mycotoxins

📷Mycotoxins are chemical compounds produced by fungi growing on organic substances such as corn, cottonseed, or peanuts that, when ingested, have some undesirable effect on humans or on an animal consuming them. Adverse effects can range from vomiting to weight loss, various types of tumors, and in some cases, death. Over one hundred toxic compounds produced by fungi have been identified, and about forty-five of these occur in grain crops. Some mycotoxins are rare in occurrence while others such as aflatoxin are common in some years. The seriousness of the mycotoxin problem varies with the year, the crop being grown, and the intended use of the crop product. Most mycotoxins affect the blood, kidneys, skin, or central nervous system, and some may cause cancer.

The genera of fungi of greatest importance to humans with respect to natural poisoning outbreaks are Aspergillus, Penicillium, and Fusarium. The Aspergillus flavus group produces aflatoxins (at least eighteen types known) that are considered the most important from the viewpoint of a direct hazard to human health. Aspergillus flavus is a common fungus that is found in soil, air, and decaying plant residues. Infection by A. flavus and subsequent aflatoxin production can occur in the field, in transit, or in storage. Most reports indicate that infection occurs in the field, while aflatoxin production can occur whenever the product is exposed to favorable conditions, either in the field or in storage.

Control of aflatoxin includes prevention of fungal growth, removal of toxins, and inactivation of toxin. Most control efforts have been directed toward control of aflatoxins in peanuts and corn. Hand picking, electronic sorting, and air classification accomplish control of aflatoxin in processed peanut products. Removal of shriveled, rancid, or discolored kernels has proven the most practical way of limiting aflatoxin contamination in peanuts.

Shiitake and Oyster Mushrooms Shiitake mushrooms, Lentinula edodes, are cultivated by more than ten million part-and full-time farmers in China where they are widely consumed, yet one-third of production is exported. In 1997, China produced approximately 88% of the total world output. In the United States, production of shiitake mushrooms is a relatively new enterprise, having begun only in the late 1970s. Sawdust is the most popular basal ingredient used in synthetic formulations of substrate for producing shiitake in the United States, but other basal ingredients may include straw, corncobs, or both. Starch-based supplements such as wheat bran, rice bran, millet, rye, and maize may be added to the mix. These supplements serve as nutrients to provide a more optimal growth medium. Oyster mushroom, Pleurotus spp., production increased rapidly worldwide during the 1980s and then decreased slightly during the 1990s. From 1986 to 1997, oyster mushroom production increased from 169,000 tons to 917,000 tons (a 5.4-fold increase). China was responsible for most of the production increase. In the United States, production of oyster mushrooms was 1,647 tons in 2001, up 2 percent from the previous year (USDA). In the United States, the primary ingredients used for Pleurotus spp. production are chopped wheat straw or cottonseed hulls or mixtures thereof. After completion of pasteurization (140°F for one to two hours) the substrate is cooled and spawned with the desired strain. There are several species of oyster mushrooms cultivated, with various colors of fruiting body. In Japan, bottle production of oyster mushrooms is most common. Substrate is filled into bottles, sterilized, and inoculated with Pleurotus spawn. Upon completion of the spawn run, bottle lids are removed and mushrooms emerge from the surface of the substrate. After the mushrooms are harvested they are weighed and packaged for shipment to market.

Button Mushrooms The cultivation of the button mushroom, Agaric us bisporus, originated in Paris, France. Melon growers in this region discovered how mushrooms could be grown and started cultivating them in 1650. By the mid-1700s it was discovered that A. bisporus could grow without light, and that favorable conditions for growing mushrooms prevailed in subterranean tunnels and caves. As a result, successful culture began inside the numerous caves that were excavated for building stones and for gypsum. The caves presented, from a climatic point of view, several advantages over the previous growing conditions in open air. Factors such as temperature and relative humidity were much more constant in caves compared with aboveground conditions. From France, mushroom cultivation spread to other parts of the world. By 1825, the first mushroom crops were being produced in caves in Holland. In 1865, mushroom culture entered the United States and by 1870, the industry had begun to develop. The button mushroom is produced commercially on a selective substrate prepared by composting mixtures of wheat straw, hay, corncobs, horse manure, or combinations thereof. The finished compost should have a nitrogen content of 2–2.5 percent, and to reach such a level, nitrogen-rich supplements must be added. Inorganic nitrogen supplements can be added but only to provide part of the necessary amount. Organic sources of nitrogen include oilseed meal, brewers' grain, malt sprouts, and poultry manure. Once the compost has been prepared, it is seeded with mushroom spawn that is prepared from a mother culture maintained by a spawn laboratory. Spawn is prepared by inoculating a pure culture of the mushroom onto steam-sterilized grain, usually rye or millet. Approximately one liter of spawn is used to seed a production surface that is contained in trays or beds inside environment-controlled production houses. Spawn run (vegetative growth of the mycelium) lasts ten to fourteen days, then a layer of neutralized peat moss (casing) is placed on top of the colonized compost to stimulate production of mushrooms. Approximately ten to fourteen days after casing, mushrooms are ready for harvest.