Molecular Gastronomy: Exploring the Science of Flavor by Hervé This

Author:Hervé This [This, Hervé]
Language: eng
Format: epub
Published: 2011-02-23T16:11:56.177000+00:00

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Truffles

European black truffles are all of the same species, but genetic analysis shows that Chinese truffles are something quite different.

THE BLACK DIAMOND! An immense amount of ink has been spilled in singing its praises. No food writer fails to mention its appearance on a menu, and no chef neglects to feature it when he aims for stars. For centuries the merits of the various black truffles that grow in Western Europe have been debated. The black truffle of Périgord is recognized have a quite different taste from the one found in Burgundy, and naturally the truffles found in France are claimed by the French to be far superior to those of Spain and Italy. Can science provide an objective basis for these opinions?

In Europe there are ten sorts of truffles, which is to say mushrooms of the Tuber genus. The black truffle, also called a Périgord truffle (Tuber melanospo-rum), is harvested principally in Spain, France, and Italy, but its gastronomic qualities vary from region to region. Michel Raymond and his colleagues at the Centre National de la Recherche Scientifique, the Institut National de la Recherche Agronomique (inra), and the Institut pour la Recherche et le Développement in Montpellier sought to determine whether these differences have a genetic basis.

More than 200 samples from various regions in France and Italy were analyzed. The Montpellier biologists studied satellite dna sequences, which differ substantially between species of the same genus, and observed no genetic variability in the samples of black truffles. They also compared black truffles with summer truffles (Tuber aestivum) and Burgundy truffles (Tuber unciatum).

Differences were found between the black and summer truffles, as expected, but the species boundaries between summer and Burgundy truffles turned out to be fuzzy. Subsequent studies confirmed that the latter two types must be considered distinct varieties—what biologists call a species complex.

How is the genetic homogeneity of the Tuber melanosporum species to be explained? It is believed that the last Ice Age trapped a small population of black truffles next to the Mediterranean, along with the trees on which they develop (the mushroom forms a subterranean root network, of which the truffle is only the reproductive organ). Because the black truffle matures during the winter, from November to February, its propagation was confined to the most southerly zones. During the later climatic warming, the black truffle is thought to have recolonized the regions where its favored trees first developed, as weather conditions permitted. Ten thousand years would have been enough time for the species to reestablish itself in southern Europe but not enough time for it to evolve.

During the same period, by contrast, summer and Burgundy truffles, which mature in spring and fall, respectively, are thought to have been confined to a more northerly area. Certainly the fact that they are found in countries further to the north and east of France proves that they are able to tolerate colder climates. The current genetic diversity of species therefore results from the fact that present-day truffles are descended from a numerous and varied population.

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