Truffles are the fruiting bodies of fungi that live underground in the soil and associate with tree roots. Truffles are roundish, or irregularly shaped structures with the firmness of a mushroom. They vary in size from bean to golf ball to baseball. The fruiting body of truffles is highly prized as food. The taste of a truffle is often compared to garlic, blended with an earthy, pungent mushroom flavour. they are most often served uncooked, shaved into foods such as salads, omelets or mushroom appetizers.
In scientific terms, truffles are a group of (mostly) edible mycorrihizal fungi. The most well known truffles are of the genus Tuber, class Ascomycetes. Truffles form a symbiotic relationship with their host plant, such as oak, hazelnut, beech or birch trees. Truffles belong to a group called the Ectomycorrihizal fungi because they form a sheath around the root tips of their host plant. From this sheath, tongues of tissue run in between the outer layers of the root to produce a three-dimensional structure called a Hartig net. On the outside of the sheath, fungal hyphae run out into the soil. It is this structure that allows an exchange of elements between the fungus and the tree. The fungus gets carbohydrates from the tree and in return helps the tree take up water, mineral salts and metabolites.
The prized truffle species (see the Edible Truffles tab) are now quite rare in the wild, mostly because the oak and beech forests in which they are found are much reduced in acreage. Ian Hall suggests that the knowledge of the location of truffle beds was lost in the world wars. French truffle production in 2008 was about 50 tonnes, down from about 1000 tonnes in 1902. Additional reasons advanced for the decline include the introduction of exotic forest tree and truffle species, poor forest management, indiscriminate harvesting of truffles, the spread of dense forest with the retreat of agriculture, and climate change.
Contrary to folklore, truffles can be cultivated. In 1808, Joseph Talon from Apt had the idea to sow some acorns collected at the foot of oak trees known to host truffles in their root system. His experiment was successful, and so his was the first known cultivated truffiére. In 1847, August Rousseau of Carpentras, planted seven hectares of oak trees and subsequently harvested large quantities of truffles.
In the early 1970's a team of French scientists, known as Truffe Agronomique developed a way to inoculate the roots of oak trees with pureed Tuber melanosporum truffles. Their technique, which they kept confidential, and patented, was to bathe the roots, under laboratory conditions of sterility, in a fertilized slurry of water and truffle spores. The seedling was then planted, and if the inoculation was successful, in 5 to 10 years, truffles could be found among the roots of the trees. Thirty-five years later, their company website advertises host truffle trees for sale. Today, as much as 80% of French grown Perigord Truffles are cultivated.