A truffle is the underground fructification of a mushroom within the Tuber genus. Although some mushrooms can grow on decaying organic matter, truffles need to establish symbiosis with tree roots in order to develop. This ectomycorrhizal relationship between the tree and the mushroom has eluded us for a very long time. Indeed, even though Egyptians had already praised the wonders of truffles 2600 years B.C., the first successful truffle cultivation attempt has only been recorded in 1810.
Cultivated species
Out of more or less 200 truffle species, only a few are cultivated. The black Périgord truffle, Tuber melanosporum, is probably the most renowned of them, whereas the white Piedmont truffle, Tuber magnatum, is the most expensive. The climate of Québec is however unfavourable to the culture of both species. ArborInnov thus selected three other truffles of gastronomic essence to cultivate.
Burgundy Truffle
(Tuber uncinatum)
This 2 to 10 cm mushroom can be found from September through December.
The Burgundy truffle has been around for a longer period of time than its Périgord counterpart. Still, we are less familiar with the former in North America. Gourmets, prepare to be seduced by the remarkable bouquet of Tuber uncinatum: an exquisite earthy aroma enriched by a generous splash of hazelnut and almond. Outstanding in salads, on pasta, or with cheese!
It is worth noting that the summer truffle (Tuber aestivum) is actually the Burgungy truffle developing under different environmental conditions.
Bianchetto Truffle
(Tuber borchii)
This 1 to 10 cm truffle can be found between January and April.
This white truffle is hardier than her Piedmont cousin. Although sometimes overlooked by gourmets, it is an honorable alternative to the pricey Tuber magnatum, worth around 4000$CAD/kg. The trick of the trade is to harvest the Bianchetto just at the right moment, when its bold garlicky fragrance is well-balanced. Only then will one truly grasp how this little gem found its way to our kitchens. To be enjoyed grated over hot dishes, or simply raw!
Appalachian Truffle
(Tuber canaliculatum)
This 2 to 12 cm truffle can be harvested
from August to December.
Who would have though North America nurtured a truffle capable of pleasing the most selective palates? Very chic with its cinnamon-colored skin and black and white flesh, the Appalachian truffle is one of our local best kept secrets. Its powerful sweet and musky aroma adds an exquisite touch to risotto, pasta, or eggs.
The truffle life cycle
A truffle is a symbiotic hypogeal mushroom. Aside from their lack of chlorophyll, and thus their lack of photosynthesis capabilities, mushrooms also differ from plants regarding their life cycle. The cycle of true and false truffles, since totally performed underground, is called hypogeal. Moreover, it can only be completed if the mushroom develops a special association with tree roots, from which both partners benefit: a symbiosis.
1. Soil Mycelium
The delicious truffle, chanterelle, or cep we love to eat are to mushrooms as the apple is to apple tree: a fructification structure. However, if trees are rather large and visible organisms, higher mushrooms are much more secretive. Not only do they live buried underground or in organic matter, but they are also microscopic. Indeed, the mycelium of these mushrooms is composed of 4 to 6-microns wide hyphae. This is approximately 15 times smaller than an average hair!
By doubling their cells, truffle mushrooms spread their hyphae to prospect the environment in search of nutrients and roots with which establish symbiosis. Up to 600 meters of hyphae live in a single teaspoon of soil, and this network can shuttle nutrients and information for over a few meters!
2. Roots Infection and Mycorrhizae Development
Truffle mycelium and tree roots send chemical signals in the soil in search of a symbiosis partner. They follow the chemical trail they detect and grow toward one another until they meet. Truffles are not selective symbiosis partners: they can and will infect many tree species.
As soon as the tree and the mushroom are in contact, truffle hyphae wrap around small roots and thread between the external root cells. This close contact between the roots and the mushroom creates the Hartig net, a cellular network where both symbiosis partners exchange nutrients. The mushroom prospects the soil to provide water, phosphorus, nitrogen, calcium, potassium, and micronutrients. In return, the tree synthesizes and supplies sugars, amino acids, and vitamins.
Once associated, the mushroom and the root will become a new structure called ectomycorrhiza (Greek: ektos, “outside”, mykós, “fungus”, riza, “roots”). Although the appearance of ectomycorrhizae differ depending on the truffle specie, they all form small root bulges up to 8mm long. Appalachian truffle mycorrhizae can be spectacular: very branched, they often grow into clusters called glomerulus.
3. Fructification
Truffle mycelium can reproduce asexually when the mycelium breaks and keeps growing, or with asexual spores. Even though asexual reproduction is simple, it doesn’t allow adaptation to environmental changes through genetic diversity. Truffle mycorrhizae thus periodically produce reproduction structures, named ascocarps, which we love to put on our plate!
Ascocarp production triggering factors are not completely understood yet. However, physiological shock, such as root pruning, or temperature and soil humidity fluctuations, seem important in the process.
4. Maturation
Many soil factors are involved in ascocarp maturation, such as pH, structure, organic matter content, and humidity. These environmental conditions, as well as the truffle specie, influence the length of the maturation, which is completed within 3 to 10 months after fructification initiation.
A ripe appearance is not a sign of maturity for truffles, since the internal tissues complete their maturation long after the external envelope, the peridium, is completely formed. When immature, the internal tissue of truffles, or gleba, is a light cream color. As the ascocarp matures, ascospores, the equivalent of seeds for fruits, develop a dark brown shade. Brown fertile veins containing the asci are thus easily distinguished from the sterile white veins in mature truffles.
5. Asci Release
Only mature ascocarps emit their characteristic delightful aroma, which encourage animals to look for and eat them. This journey through the digestive system of animals releases the asci, small pouches containing the ascospores, from the ascocarp. The ascospores can then germinate, often far from their original location. Winter temperatures will degrade the ascocarps which were not eaten by animals to release the asci.
Truffle identification can be performed by microscopic analysis of asci and ascospores. However, even though this method is valid when performed by an expert, genetic analysis remains the most precise way of identifying a truffle.
6. Ascospore Germination
Ascospores are designed to withstand adverse conditions, such as drought or extreme temperatures, until the environment becomes more favorable to germination. Although factors triggering germination are not fully understood yet, root proximity seems an important variable; ascospores most likely detect the sugars secreted by the roots.
ArborInnov offers quality truffle plants. Please contact us to request for a quotation.
