Though common to many countries, and comprising numerous species, the truffle attains its greatest excellence in France, unless the white truffle of Italy, which is considered equally good by many, be excepted. Its chosen haunts are clayey soils mixed with sand and limestone, moist, shaded, and temperate localities, southerly and easterly expositions, protected slopes, and especially the umbrage of oaks, as also of aspens, black poplars, nut-trees, yoke-elms, willows, and white birches. Limestone or carbonate of lime is accounted as necessary to its formation, while the presence of iron imparts to it an added firmness and aroma. Despite persistent efforts, all attempts to cultivate it have proved fruitless. It is only of recent years that it has become known in part how it is propagated or how it grows. Among trees, the oak is its most favoured companion, its artificial production having been accomplished wholly through the cultivation of oaks and certain other trees in soils and expositions corresponding to its natural habitat.
By general consent Périgord is credited with producing the best truffles, the next in commercial repute being those obtained from Provence and Dauphiné; the finest of the former come from the canton of Sarlat, the best of Dauphiné from the cantons of Tain and Valence. Among authorities, Beauvilliers preferred the black product of Provence (T. melanosporum), of which there are two varieties, the so-termed violet and the grey; and Savarin the white species (T. magnatum), obtained preferably from Piedmont, where it occurs beneath poplars and oaks during summer. The whitish-brown truffle of Italy, in its early stage, similar to the whitebait described by Thackeray, possesses an "ambrosial flavour," and is difficult to surpass, combining as it does all the most ethereal qualities of the Allium tribe with the dulcet pungency of Gorgonzola when in its freshest flower. A species exists which emits a powerful scent of musk, while numerous others occur with odours so rank as to be utterly unfit for edible purposes. Northern Spain produces excellent truffles, but these are comparatively short-lived. T. æstivum, called "summer truffle," indigenous to many countries, is extremely plentiful in southern France. It is common to England, where it grows most frequently under beech-trees. This exhales a strong and penetrating smell which has been compared to that of sheep-folds. The effluvium of garlic is always very marked in the white truffle of Italy, and by some it is said to recall the odour of garlic mixed with onion, high game, and matured cheese. After standing for a time, when its garlic flavour has become somewhat modified, it is also suggestive of the flavour of vegetable-oysters. Indeed, the truffle is as strange in its odours as it is in its manner of growth, and in certain respects it brings to mind some characteristics of that strangest of flowers, the orchid.
From November to March is the season when the prized dark tuber is most abundant, and during which its highest qualities are evolved. The black pearl of Provence and Périgord begins to take on its rich ebon hue in October, lasting until April: æstivum and its varieties being gathered during May and June in Provence, and from October to January in Burgundy and Champagne. The species of greatest repute in southern France is found at variable depths, mostly beneath certain oaks known as chênes truffiers, or truffle-oaks. With it often occurs another species, T. brumale, which is likewise held in much esteem and figures as a large commercial factor. Among the inhabitants the truffle harvest forms an extensive industry; pigs, dogs, and professional hunters being utilised for the quest, and the crop always commanding high prices, which are fixed by the Paris market. When the supply happens to be short, many inferior species are substituted or are mixed with the genuine.
Of recent years artificial truffières have been largely planted in the favoured districts of southern France. To M. Rousseau, a proprietor of Vaucluse, has been erroneously ascribed the discovery of this means of production. Already during the middle of the eighteenth century M. de Montclar, procureur-général at Aix, discovered truffles as the result of sowing acorns on his lands; but, the truffles disappearing subsequently, no further attention was paid to the matter, and the relation between cause and effect passed unnoticed or was forgotten. Since then Poitou, Périgord, and Provence have each claimed to be the discoverer of artificial truffle culture. It is within a comparatively short period only that the merit of originating the system, now a source of great revenue, was adjudged, after painstaking investigation, to Joseph Talon, a small landholder of Vaucluse, who about eighty years ago sowed some acorns in an unremunerative piece of ground. Ten years afterwards, while passing through the plantation with the pig he employed in hunting, he was not a little surprised to find truffles beneath the oaks; when, recollecting that he had obtained the acorns from a truffle-oak, he repeated the sowing on another plot, which in course of time proved equally successful. The theory was established beyond a doubt, and the result finally became generally known, despite his efforts to keep it secret.
Many unsuccessful attempts at artificial truffle-raising have been made. In 1830 Alexander Bernholz, a German, published a long treatise on the subject, his theory being that by planting truffles in soil composed of certain ingredients, and in localities and expositions corresponding to their natural habitat, they could be successfully grown. Count Noé, in the south of France, is said to have succeeded in raising truffles in his woods by irrigating the ground, after a certain degree of preparation, with water in which the skins of truffles had been rubbed. But this statement, as well as other reputed successful attempts at reproduction, would not seem to have been borne out in France, where the planting of young truffle-oaks, the acorns of truffle-oaks, or certain other truffle-producing trees alone has accomplished the desired result.
In artificial plantations the truffles form in from six to ten years, usually disappearing when the trees are twenty-five or thirty years old. Then, after a variable period of non-production, the tuber often forms again. As the truffle-tree develops, the vegetable growth which surrounds it begins to decline, a certain index that truffles are commencing to form—the ground round a truffle-producing tree being always sterile. When the truffles cease the herbage again appears.
Though many unsatisfactory reasons have been ascribed for the phenomenon, it has been traced by M. Grimblot to the simple fact that the filaments of the mycelium invade and destroy the roots of herbaceous vegetation. Similarly, vegetation asserts itself when the cause is removed. With young trees the truffles are usually found close to the trunk, whereas with old trees they generally appear near the periphery of the circle formed by the outer roots, as well as at a distance further removed, but usually within the shade of the tree. To what extent the humus of the soil formed by the droppings of the leaves is responsible is not stated. In many respects the subject remains, as it has always remained, a complex phenomenon that baffles the naturalist, who is usually content to refer to the truffle as an "underground fungus," or "an order of sporidiiferous fungi of subterranean habit." Perhaps the definition of Dr. C. de Ferry de la Bellone, which may be summarised as follows, is as accurate as any: "A subterraneous mushroom with a mycelium or filamentous body, from which it is developed, like the mushroom, and which requires the roots of certain trees for its formation."[52] The theory that the truffle owes its genesis to the roots of trees, or is in some mysterious manner connected with them, might be accepted as satisfactory were it not that species are also found in open places where the argument could not apply.
While the roots of most kinds of oaks, both deciduous and evergreen, appear to be favourable for its generation, it has been found that in a given region the best species to propagate are those which have already produced the tuber in the locality in question, certain varieties seeming to be more liable to reproduce it than others. Climate, altitude, and exposition are also to be considered as regards the choice of the kinds selected for plantations. The arboriculturist and mycologist will be interested in the various truffle-producing oaks that may be utilised, according to the site, soil, and climatic conditions. These embrace the following species and varieties: Quercus pedunculata, Q. ped. pubescens, Q. semi-ped., Q. sessiliflora nigra, Q. nigra sessil. glabra, Q. nigra sessil. pub., Q. sessil. pub., Q. sessil. laciniata, Q. sessil. magna pubes, Q. ilex, Q. coccifera. All kinds of nut-trees are likewise favourable to its production, and may be planted almost indiscriminately. The range of T. melanosporum is broadly defined as between latitude 49° north and 40° south; the question of quality depending, like that of many other esculents, largely on climate and habitat. As in the same vineyard certain portions yield a superior wine, so on particular slopes of localities that favour the truffle a product of finer quality is obtained.
Besides the usual means of locating the truffle, its presence is revealed by several species of coleopterous and dipterous insects which, during late autumn and winter, on temperate days swarm in the truffle-woods, attracted by the scent. These insects seek the tuber in which to deposit their eggs, and are observed entering and leaving the ground—a circumstance which gave rise to the opinion that the truffle was only a gall. This form of truffle-hunting is practised chiefly by poachers, and is known as la chasse à la mouche.
The statement that the canned truffle is but a shade of its original will bear modifying in certain instances where only the best species have been utilised, after scrupulous selection, before they are wormy or overripe, and where they have been preserved by the "Appert process," au naturel, without oil, brandy, or vinegar, in hermetically sealed cans, and used before they have been thus preserved for a long period. Under these conditions the species melanosporum and magnatum retain no little of their pristine virtues, and may still glorify a sauce or dignify a Châteaubriand. To the skill of the cook the result will be principally due. Inasmuch as the truffles have already been subjected to several hours' ebullition, they should only be finely sliced and gently heated in order that their flavour may not be dissipated by the cooking. The dish they are to grace should be prepared first, and so soon as the truffles are ready it should be immediately served under cover. Perhaps as good a medium for utilising the preserved product is a steak with a bordelaise sauce in which garlic or shallots should figure very lightly. The comparative excellence of the preserved truffle will depend, of course, upon freshness and the probity and care of the merchant.