Black truffle, Public Domain
(Click on the following link to listen to an audio version of this blog …. Truffles
Truffles are very famous fungi. They are packed with complex chemicals that give some of them deep, musky, earthy flavors which they contribute to food even when added in very small quantities. Since truffles sell for astronomical prices (white truffles often cost $4000 a pound and black truffles cost $300 to $800 a pound), careful to outright stingy use of them in cooking seems extremely logical.
“Truffle” is both the common name of a diverse group of subterranean fungi and also the name of their edible fruiting bodies. Many truffle species, like the white and black truffles mentioned above, are in genus Tuber, but there are over a hundred other genera of fungi that have species that are called “truffles.” All truffles exhibit the fungal tendency to synthesize a diverse array of chemicals, and they make these chemicals in very large quantities. When you dig up a truffle, the scent of its chemical array can be overwhelming! A truffle loses its scent very rapidly after it is dug up and detached from its supportive mycelia. It must, therefore, be transported to market and used as quickly as possible after harvesting.
Some of the truffle chemical arrays are pleasing to human tastes and olfactory perceptions (like the deep flavors of the white and black truffle). Other truffles generate less pleasant but equally intense aromatic chemical arrays. Some of these other “truffle-scents” have been described as resembling sewage gases or baby diarrhea. Not something that would fit in haute cuisine!
Truffle in ground. Photo E. Johnson, Cambrideg Univeristy
All fungal species labeled as “truffles” are mycorrhizal fungi that form associations with the roots of trees or shrubs. These fungal mycorrhiza are ectomycorrhiza and, so, grow on the outside of a root with a mantle of connecting material holding the mass of the surrounding hyphae and the root together. Many different tree species have associated truffle mycorrhiza. Notably oaks, beeches, birches, hazels, pines and poplars form mycorrhizal associations with the most edible and commercially valuable truffle fungi.
The life cycle of a truffle is complex and full of potential failure points. The truffle fungi, apparently, are not very robust and are easily ousted from their ectomycorrhizal positions on the tree and shrub roots by other, more aggressive fungal species. Also, it takes many years for truffle fungi to grow large enough to begin to form fruiting bodies. Any diseases of or damage to the supportive tree or shrub during this period of time can short-circuit the formation of the fruiting bodies.
There is also a suggestion that the truffle fungus needs to have very specific soil bacteria associated with it in order to synthesize the full array of aromatic chemicals! Truffles, then, like grapes take on many of their subtle (and highly valued) flavors only when grown in certain soils. This truffle “terroir” can make huge differences in the market price of the harvested truffles!
Lucy, a trufle hunting dog. Phto by E. Johnson, Cambridge University
The final life cycle problem of truffle fungus is how to get the spores in its subterranean fruiting body to be dispersed out through its surrounding environment. This dispersal is via frugivorous animals. The fruiting body needs to be eaten by a squirrel, vole, gopher, chipmunk, deer or bird, and the spores must then pass through the animal’s digestive tract and, thus, get spread about the environment in the animal’s feces. In order to be noticed by these animals, the fruiting body emits its complex mix of volatile odor chemicals!
Because of the complexity of the environmental needs of the truffle fungus, truffles have historically been harvested from natural, forested habitats where all of the complexities of truffle biology are handled by natural, ecological processes. Roving truffle hunters hike through pristine woodlands, following their trained scent animals (usually dogs or pigs) (both dogs and pigs have exquisitely sensitive noses and can be easily trained to find truffles) to the scattered locations of truffle development. The hunters can dig up thousands of dollars-worth of truffles each day! This scenario is acted out in France, in Italy and in the United States each year as the wild truffles mature. The truffle hunter and their dogs or pigs dig out the hidden truffles (they are usually a few inches to a foot below the soil surface) and it is often a battle between hunter and his dog (or pig) to unearth and bag up the truffle without the scent animal eating them first! Interestingly, truffle hunting pigs are no longer allowed in Italy because of the extensive damage they do to the truffle mycelia when they dig out the truffles. Pigs are also very hard to control when they smell a truffle!
Truffle scent animals vigorously seek out the hidden fruiting bodies. One truffle dog owner remarked that his dog, Dante, acted as though “he sensed god living just below the surface of the soil” and rapturously sought to unearth him! One difficulty truffle scent animal handlers have is rewarding their animals for finding the truffles. A bit of liver is no substitute for a mouthful of truffle!
Natural habitats suitable for wild truffles have been declining over the past century. Changes in agricultural practices, changes in land use and changes in life styles have all contributed to declines of truffle-friendly, pristine woodlands. There has been a concerted effort, then, to translate the truffle-supportive woodland ecosystem into managed, cultivated plantations.
Truffle farm in France. Photo P. Sourzet, Scielo
Beginning in the late 1960’s and 1970’s, truffle plantations began to successfully grow truffles, and by the 1980’s these plantations had been established in many countries around the world. About 80% of the truffles produce in France are now grown on plantations. Establishment of these plantations is a difficult, delicate process requiring precise analysis of soils, healthy tree species and control of potentially competing fungal species. Also, the truffle plantations must be secured by strong fences to keep out wild animals (like wild boars!) who are attracted to the compelling scent of the maturing truffles.
The time it takes to establish a truffle plantation and the cost to manage and protect it, make truffle farming a very expensive and risky business. The potential yield and incredible payoff, though, make this risk worth taking.
There was a recent article in the New York Times (November 11, 2023) describing a declining crop of wild truffles in Italy. The dry summer and fall of the past few years (all attributed to climate change) have stressed the trees that symbiotically support the truffle fungi causing a precipitous decline in truffle fruiting bodies. The continued decline in these vital tree species could lead to the extinction of the wild truffle. A catastrophe of unspeakable proportions!
(Next week: lichens!)