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Truffle Aroma

Organic aromas are due to volatile essences composed of a multitude of odorous compounds.  These aromatic essences are controlled genetically and synthesised by the plant or fungus’ own metabolites rather than by microbes in the surrounding soil.  Truffle essence synthesis is a biological process similar to that of essences produced by aromatic plants and fragrant flowers, but is unlike the fermentation process involving yeasts that produces the flavour of wine.

Truffle essences are composed of volatile compounds of very low molecular weight, referred to as C8-VOCs (volatile organic compounds containing 8 carbon molecules or less), as compared with essences from aromatic plants that are typically composed of monoterpenoids (molecules of 10 carbon atoms) and sesquiterpenoids (molecules of 15 carbon atoms).

The truffle essences are therefore highly volatile and their aromas readily diffuse through the soil to reach the ground surface and attract animal vectors for spore dispersal.  Some truffle aromas are also very intense, though the scent will dissipates fairly quickly once the truffles are removed from the soil and exposed to the air.  Nevertheless, so intense and pervasive is the aroma that for a while, a walnut size winter black truffle will perfume a room, while a similar size winter white truffle will perfume an entire apartment!

Although they are similar types of organism, truffles do not smell the same as mushrooms.  The alcohol, 1-octen-3-ol, responsible for the mushroom odour, and also an extremely potent olfactory attractant for many insects, is produced in young truffles but diminishes as they mature.  It is only present in some truffle species at low concentrations, while not at all in others at maturity.  This alcohol is the most abundant compound occurring in mushrooms and is also a typical component in general of odorous body emanations of humans and animals, occurring in human sweat and breath and contributing to the sweaty appeal of fungi.

The truffle aroma is both much more intense and characteristically different from that of mushrooms, composed of initial sweet notes that are variously fruity, malty, nutty or spicy from alcohols, aldehydes, ketones and esters, leading to the more distinctive combination of savoury notes from sulphides, modified by musky notes from phenolic ethers. 

The degree of pleasantness to the human sense is determined by how well the contrasting notes are balanced and harmoniously combined, and especially how well the sulphides are controlled. If the sulphides are too pronounced, the whole aroma will smell unpleasant.  Pure sulphides have an extremely obnoxious odour but they can be modified by other odorous compounds of equal intensity into a more complex and interesting aroma.  Phenolic ethers have a pungent-musky vegetable quality and a comparably high odour intensity capable of altering the sulphides to a significant degree.  When suitably modified, sulphides provide the crucial savoury quality to truffles.

The various types of truffle differ in both odour intensity and odour character, according to the type and proportion of compounds in their essences.  In the individual character notes, the savoury-musky quality determined by the sulphide and phenolic ether combination is decisive for the truffle’s gastronomic appeal, while the sweet-nutty aroma contributes contrasting notes, resulting in an altogether delicately rich and complex aroma profile.

The balance within the savoury-musky quality is more attractive when the savoury notes are more pronounced than the musky ones.  In the savoury dominant flavoured truffles, the winter white has the best ratio of 45% savoury to 10% musky.  Where the ratio is predominantly savoury, at 70% in the smooth black and 40% in the Durone white, to almost no musky notes, the overall flavour is still pleasant, although much less interesting, but where the musky notes are more dominant than the savoury ones, at 26% to 10% in the Chinese black and 15% to 7% in the autumn black, the overall appeal is significantly diminished.

Among the sweeter flavoured truffles where the savoury quality is milder, the winter black has the best flavour with 12% savoury and only trace amounts of musky notes, while the summer black has 10% savoury, and the muscat black 8%, with similarly low levels of musky notes.

The musty-mushroom note that only appears in the autumn black and the shiny truffle is not significant to the truffle character.

The winter white truffle has the finest flavour of all truffles, being the most richly savoury.  Compared to the three savoury truffles (winter white, Durone white and smooth black), the other truffles have a far less pungent and more delicate, sweeter flavour.

 

Truffle Essence Components

Truffle aromas are determined by a combined gas chromatography and mass spectrometry (GC/MS) technique. Gas chromatography separates out the individual molecular components by their evaporation rates and determines the quantity of each by their retention times, while mass spectrometry identifies the compounds by the light spectrum of their molecular mass.

The earliest studies of the aromatic constituents of truffles were conducted shortly after the first GC/MS instruments were developed during the 1950s. As instruments are less sensitive than biological systems, including the human nose, there will evidently be further improvements in future and the number of truffle volatiles identified in the future will increase.

In 1980, the key volatiles of the Perigord black truffle (Tuber melanosporum) were first described. Since this pioneering work, more than 30 papers dealing with truffle volatiles (from both fruiting bodies and mycelia) have been published in national and international scientific journals. Until the year 2000, most publications investigated the two species in which there is the greatest commercial interest: the Perigord black truffle (T. melanosporum) and the Piedmont white truffle (Tuber magnatum).

The aroma profiles of the essences of twelve species of truffles were published in the Proceedings of the 10th International Flavour Conference held in Paros, Greece in Jul 2000. This publication provides an insight into the complex aroma quality of each truffle and the differences between the aromas of these important culinary truffle species. [T Talou, M Doumenc-Faure and A Gaset (2000) Flavour Profiling of 12 Edible European Truffles. Proceedings of the 10th International Flavour Conference, Paros, Greece.]

A total of 38 components were identified, 23 of which are major components contributing to the truffle aroma:

The sweaty-musky aroma of truffles is similar to that of the pheromone androstenol (C19 H30 O) that also occurs in humans - in the sweat of men and the urine of women. This may account for the strong attraction truffles have for people and their historical reputation as aphrodisiacs. Research in England in 1982 showed that when men and women were (unknowingly) exposed to this substance, both genders found normal photographs of women more sexually attractive.