Truffle

thumb|[[Tuber melanosporum|Black truffle (Tuber melanosporum)]]

A truffle is the fruiting body of a subterranean ascomycete fungus, one of the species of the genus Tuber. More than one hundred other genera of fungi are classified as truffles including Geopora, Peziza, Choiromyces, and Leucangium. These genera belong to the class Pezizomycetes and the Pezizales order. Several truffle-like basidiomycetes are excluded from Pezizales, including Rhizopogon and Glomus.

Truffles are ectomycorrhizal fungi, so they are found in close association with tree roots. Spore dispersal is accomplished through fungivores, animals that eat fungi. These fungi have ecological roles in nutrient cycling and drought tolerance.

Some truffle species are prized as food. Edible truffles are used in Italian, French and other national . Truffles are cultivated and harvested from natural environments.

thumb|White truffles from [[San Miniato]]

thumb|Black truffles from San Miniato

Taxonomy

Species

Black

thumb|Black Périgord truffle, cross-section

The black truffle or black Périgord truffle (Tuber melanosporum), the second-most commercially valuable species, is named after the Périgord region in France. Black truffles associate with oaks, hazelnut, cherry, and other deciduous trees and are harvested in late autumn and winter. The genome sequence of the black truffle was published in March 2010.

Summer or burgundy

thumb|Summer truffles in a shop in Rome

The black summer truffle (Tuber aestivum) is found across Europe and is prized for its culinary value. Burgundy truffles (designated Tuber uncinatum, but the same species) are harvested in autumn until December and have aromatic flesh of a darker colour. These are associated with various trees and shrubs. of the Piedmont region in northern Italy, and most famously, in the countryside around the cities of Alba and Asti. A large percentage of Italy's white truffles also come from Molise.

Truffles are subterranean, highly prized fungi () that grow on tree roots, often selling for thousands of dollars per pound due to their rarity and intense, savory umami flavor. They are found underground, usually with oak or hazelnut trees, and were historically hunted using pigs, though dogs are now preferred.

Whitish

The "whitish truffle" (Tuber borchii) is a similar species native to Tuscany, Abruzzo, Romagna, Umbria, the Marche, and Molise. It is reportedly not as aromatic as those from Piedmont, although those from Città di Castello are said to come quite close.

The pecan truffle (Tuber lyonii) syn. texense is found in the Southern United States, usually associated with pecan trees. Chefs who have experimented with them agree "they are very good and have potential as a food commodity". Although pecan farmers used to find them along with pecans and discard them, considering them a nuisance, they now sell for about $160 a pound and have been used in some gourmet restaurants.

Beyond Tuber

The term "truffle" has been applied to several other genera of similar underground fungi. The genera Terfezia and Tirmania of the family Terfeziaceae are known as the "desert truffles" of Africa and the Middle East. Pisolithus tinctorius, which was historically eaten in parts of Germany, is sometimes called "Bohemian truffle".

Geopora spp. are important ectomycorrhizal partners of trees in woodlands and forests throughout the world. Like other truffle fungi, Geopora produces subterranean sporocarps as a means of sexual reproduction. Like their ascomycete counterparts, these fungi can create truffle-like fruiting bodies. In addition to their ecological importance, these fungi hold economic value, as well. Rhizopogon spp. are commonly used to inoculate coniferous seedlings in nurseries and during reforestation. These fungi form mycelial mats of vegetative hyphae that may cover 25–40% of the forest floor in Douglas fir forests, thereby contributing to a significant portion of the biomass present in soils. Members of this genus have low host specificity, associating with a variety of plants including hardwoods, forbs, shrubs, and grasses. Within the order Pezizales, subterranean fungi evolved independently at least fifteen times. Molecular clockwork has suggested the evolution of ectomycorrhizal fungi occurred approximately 130 million years ago.

The evolution of subterranean fruiting bodies has occurred numerous times within the Ascomycota, Basidiomycota, and Glomeromycota. using internal transcribed spacers (ITS) of nuclear DNA and revealed five major clades (Aestivum, Excavatum, Rufum, Melanosporum and Puberulum); this was later improved and expanded in 2010 to nine major clades using 28S large subunits (LSU) rRNA of mitochondrial DNA.

The truffle habit has evolved independently among several basidiomycete genera. Phylogenetic analysis has revealed that basidiomycete subterranean fruiting bodies, like their ascomycete counterparts, evolved from above ground mushrooms. For example, Rhizopogon species likely arose from an ancestor shared with Suillus, a mushroom-forming genus. This then entered other languages through Old French dialects.

Ecology

The mycelia of truffles form symbiotic, mycorrhizal relationships with the roots of several tree species, including beech, birch, hazel, hornbeam, oak, pine, and poplar. Mutualistic ectomycorrhizal fungi such as truffles provide valuable nutrients to plants in exchange for carbohydrates. Ectomycorrhizal fungi cannot survive in the soil without their plant hosts.

Tuber species prefer argillaceous or calcareous soils that are well drained and neutral or alkaline. Tuber truffles fruit throughout the year, depending on the species, and can be found buried between the leaf litter and the soil. Most fungal biomass is found in the humus and litter layers of soil. Conidia can be produced more readily and with less energy than ascospores and can disperse during disturbance events. Production of ascospores is energy intensive because the fungus must allocate resources to the production of large sporocarps. Many species of trees, such as Quercus garryana, are dependent on the dispersal of sporocarps to inoculate isolated individuals. For example, the acorns of Q. garryana may be carried to new territory that lacks the necessary mycorrhizal fungi for establishment. Following germination, hyphae form and seek out the roots of host plants. Arriving at roots, hyphae begin to form a mantle or sheath on the outer surface of root tips. Hyphae then enter the root cortex intercellularly to form the Hartig net for nutrient exchange. Hyphae can spread to other root tips colonising the entire root system of the host. though this is not always the case.

Nutrient cycling

Truffle fungi are ecologically important in nutrient cycling. Plants obtain nutrients via their fine roots. Mycorrhizal fungi are much smaller than fine roots, so they have a higher surface area and a greater ability to explore soils for nutrients. Acquisition of nutrients includes the uptake of phosphorus, nitrate or ammonium, iron, magnesium, and other ions. Because these mats are nitrogen sinks, leaching of nutrients is reduced. Microscopic arthropods such as mites feed directly on mycelium and release valuable nutrients for the uptake of other organisms. Thus, truffle fungi and other ectomycorrhizal fungi facilitate a complex system of nutrient exchange between plants, animals, and microbes.

Importance in arid-land ecosystems

Plant community structure is often affected by the availability of compatible mycorrhizal fungi. In arid-land ecosystems, these fungi become essential for the survival of their host plants by enhancing the ability to withstand drought. A foundation species in arid-land ecosystems of the Southwest U.S. is Pinus edulis, commonly known as pinyon pine. P. edulis associates with the subterranean fungi Geopora and Rhizopogon.

As global temperatures rise, so does the occurrence of severe droughts, detrimentally affecting the survival of aridland plants. This variability in climate has increased the mortality of P. edulis. Therefore, the availability of compatible mycorrhizal inoculum can greatly affect the successful establishment of P. edulis seedlings.

Several truffle species and varieties are differentiated based on their relative contents or absence of sulfides, ethers or alcohols, respectively. The sweaty-musky aroma of truffles is similar to that of the pheromone androstenol that also occurs in humans. , the volatile profiles of seven black and six white truffle species have been studied.

Extraction

thumb|A trained truffle hunting [[pig in Gignac, Lot, France]]

thumb|A trained truffle hunting [[dog in Mons, Var, France]]

{| class="wikitable"

|+Comparison of truffle dog and pig

!Truffle dog

!Truffle pig

|Keen sense of smell

|Must be trained

|Innate ability to sniff out truffles

|Easier to control

|Tendency to eat truffles once found

Because truffles are subterranean, they are often located with the help of an animal (sometimes called a truffler) possessing a refined sense of smell. Traditionally, pigs have been used to extract truffles. Both the female pig's natural truffle-seeking and her intent to eat the truffle were thought to be due to a compound within the truffle similar to androstenol, the sex pheromone of boar saliva, to which the sow is keenly attracted. Studies in 1990 demonstrated that the compound actively recognised by both truffle pigs and dogs is dimethyl sulfide.

For discovering how to cultivate truffles, some sources now give priority to Pierre II Mauléon (1744–1831) of Loudun (in western France), who began to cultivate truffles around 1790. Mauléon saw an "obvious symbiosis" between the oak tree, the rocky soil, and the truffle and attempted to reproduce such an environment by taking acorns from trees known to have produced truffles and sowing them in chalky soil. His experiment was successful, with truffles found in the soil around the newly grown oak trees years later. In 1847, Auguste Rousseau of Carpentras (in Vaucluse) planted of oak trees (again from acorns found on the soil around truffle-producing oak trees), and he subsequently obtained large harvests of truffles. He received a prize at the 1855 World's Fair in Paris.

thumb|A truffle market in [[Carpentras, France]]

Others imitated these successful attempts in France and Italy. In the late 19th century, an epidemic of phylloxera destroyed many of the vineyards in southern France. Another epidemic killed most of the silkworms there, too, making the fields of mulberry trees useless. Trufficulture became an important source of income for those affected. The calcareous and exposed vineyard soils were well-suited to the cultivation of truffles. Reasons given for this decline include the Industrial Revolution, the subsequent rural flight and the multiple European wars of the 20th century, which reduced the rural population. About 80% of the truffles now produced in France come from specially planted truffle groves. Investments in cultivated plantations are underway in many parts of the world using controlled irrigation for regular and resilient production.

A critical phase of the cultivation is the quality control of the mycorrhizal plants. Between 7 and 10 years are needed for the truffles to develop their mycorrhizal network, and only after that do the host plants come into production. Complete soil analysis to avoid contamination by other dominant fungi and very strict control of the formation of mycorrhizae are necessary to ensure the success of a plantation. Total investment per hectare for an irrigated and barrier-sealed plantation (against wild boars) can cost up to €10,000. Considering the level of initial investment and the maturity delay, farmers who have not taken care of both soil conditions and seedling conditions are at high risk of failure.

New Zealand and Australia

The first black truffles (Tuber melanosporum) to be produced in the Southern Hemisphere were harvested in Gisborne, New Zealand in 1993.

New Zealand's first burgundy truffle was found in July 2012 at a Waipara truffle farm. It weighed 330 g and was found by the farm owner's beagle.

In 1999, the first Australian truffles were harvested in Tasmania, the result of eight years of work. Trees were inoculated with the truffle fungus to create a local truffle industry. Their success and the value of the resulting truffles has encouraged a small industry to develop.

Truffle production has expanded into the colder regions of Victoria, New South Wales and Western Australia. In 2014, over of truffles were harvested by Truffle Hill, Manjimup, Western Australia.

In June 2014, a grower harvested Australia's largest truffle from their property at Robertson, in the Southern Highlands of New South Wales. It was a French black périgord fungus weighing in at and was valued at over $2,000 per kilogram.

United States

Périgord truffles were first farmed in Tennessee in 2007. At its peak in the 2008–2009 season, one farm produced about 200 pounds of truffles, but Eastern filbert blight almost entirely wiped out the hazel trees by 2013 and production dropped, essentially ending the business. Eastern filbert blight similarly destroyed the orchards of other once-promising commercial farms in East Tennessee, while newer farms in California, North Carolina, Oregon, and Arkansas were started. , the Appalachian truffle (Tuber canaliculatum) was being developed as a potential market.

Uses

thumb|Shaved Périgord truffle with pasta at [[Spago in Las Vegas, Nevada]]

Because of their high price and their strong aroma, truffles are used sparingly. Supplies can be found commercially as unadulterated fresh produce or preserved, typically in a light brine.

Their chemical compounds infuse well with fats such as butter, cream, cheeses, avocados, and coconut cream.

As the volatile aromas dissipate more quickly when heated, truffles are generally served raw and shaved over warm, simple foods which highlight their flavour, such as buttered pasta or eggs. Thin truffle slices may be inserted into meats, under the skins of roasted fowl, in foie gras preparations, in pâtés, or in stuffings. Some speciality cheeses contain truffles, as well. Truffles are also used for producing truffle salt and truffle honey.

While chefs once peeled truffles, in modern times, most restaurants brush the truffle carefully and shave it or dice it with the skin on to make the most of the valuable ingredient. Some restaurants stamp out circular discs of truffle flesh and use the skins for sauces.

thumb|upright=0.6|Truffle oil (olive oil with Tuber melanosporum)

Oil

Truffle oil is used as a lower-cost and convenient substitute for truffles, to provide flavouring, or to enhance the flavour and aroma of truffles in cooking. Some products called "truffle oils" contain no truffles or include pieces of inexpensive, unprized truffle varietals, which have no culinary value, simply for show. The vast majority is oil that has been artificially flavoured using a synthetic agent such as 2,4-dithiapentane. It is used as a spirit in its own right, a cocktail mix or a food flavouring.

Cultural history

Antiquity

The first mention of truffles appears in the inscriptions of the neo-Sumerians regarding their Amorite enemy's eating habits (Third Dynasty of Ur, 2nd century BCE) and later in writings of Theophrastus in the 4th century BCE. In classical times, their origins were a mystery that challenged many; Plutarch and others thought them to be the result of lightning, warmth, and water in the soil, while Juvenal thought thunder and rain to be instrumental in their origin. Cicero deemed them children of the earth, while Dioscorides thought they were tuberous roots.

Renaissance and modernity

During the Renaissance, truffles regained popularity in Europe and were honoured at the court of King Francis I of France. They were popular in Parisian markets in the 1780s, imported seasonally from truffle grounds, where peasants had long enjoyed them. Brillat-Savarin (1825) noted that they were so expensive they appeared only at the dinner tables of great nobles and kept women. They were sometimes served with turkey.