Electrophoretic karyotyping, mitochondrial DNA restriction fragment length polymorphism analysis, and PCR amplification of interspersed repeats were used to study the variability, phylogenetic affinities, and biogeographic distribution of wild Saccharomyces cerevisiae enological yeasts. The survey concentrated on 42 individual wine cellars in the Charentes area (Cognac region, France). A limited number (35) of predominant S. cerevisiae strains responsible for the fermentation process have been identified by the above molecular methods of differentiation. One strain (ACI) was found to be distributed over the entire area surveyed. There seemed to be little correlation between geographic location and genetic affinity.

Fifteen indigenous strains of Saccharomyces cerevisiae, differentiated by their genetic polymorphism, were compared in standard conditions for their respective ability to produce volatile compounds during the alcoholic fermentation of grape must. The results were processed using analysis of variance and of principal components. They exhibited significant differences between strains, in particular for the higher alcohols, fatty acid esters, acetates or acetaldehyde. On the basis of their analytical profile, five strains were selected and compared on the pilot scale. Overall, the pilot results confirmed laboratory findings. As the strain effect appears to be determinant on the aromatic composition of wine spirits, a programme of selection based on both intraspecific molecular characterisation and chromatographic analysis is carried out to obtain specific yeast strains for high-quality spirits.

Grape rot can cause organoleptic deviations in wines, including the aroma of fresh mushrooms; one of the molecules responsible for this is 1-octen-3-one. The bunches affected by this defect are often contaminated by Botrytis cinerea; however, they may also contain a whitish mycelium that cannot be attributed to B. cinerea. This additional fungal growth is the subject of this study.  Several isolations of this fungus were carried out on grape bunches from different vineyards in the French Alsace and Champagne regions using a culture medium containing an anti-Botrytis fungicide (Boscalid). The sequencing of the ITS regions showed that most isolations corresponded to Crustomyces subabruptus (Bourdot & Galzin; Jülich 1978), an endophyte basidiomycete. Contamination tests carried out on bunches and grape juice with this fungus confirmed its responsibility for the appearance of fresh mushroom defects in wines, and showed that it has the capacity to produce large quantities of 1-octen-3-one in a wet and warm environment. The results of this study suggest that this basidiomycete is responsible for fresh mushroom aromas in wines.

L'étude écologique de la microflore menée sur les parcs à bois de cinq tonnelleries charentaises a permis d'isoler quatre champignons généralement présents dans les couches internes des merrains (Candida sp., Paecilomyces variotii, Phialemonium sp1 et la Souche E). L'impact des champignons sur la composition analytique du bois est net, par contre d'un point de vue sensoriel les différences par rapport au témoin non inoculé ne sont pas flagrantes. Dans les conditions de la pratique, où la biomasse fongique est beaucoup plus faible que celle obtenue sur les copeaux, la contribution des champignons aux qualités sensorielles finales du bois est donc a fortiori très vraisemblablement négligeable.Abstract : The ecological study of flora carried out in five cooperages in the Charentes has enabled the isolation of four fungi generally found in the internal layers of staves (Candida sp., Paecilomyces variotii, Phialemonium sp., and strain E). Several experiments were performed to establish how these four species affected the analytical and qualitative characteristics of the wood. Their wood degradation ability is quantified by observing the mass loss of inoculated stick of wood. The mass loss is very small. Next we measured the ability of these moulds to degrade cellulose, xylan and aesculin. In a synthetic liquid medium the four fungal species degrade aesculin and xylan, only Phalemonium sp. shows a measurable growth rate for the cellulose medium. Afterwards, the effect of the moulds on the composition and sensorial qualities of the wood is studied by direct inoculation of wood shavings. After three months of incubation, shavings, eventually after heating, are soaking in white spirit of Cognac under standard conditions ; this enables, the production of extracts which may be analysed and tasted. When extracts are prepared from unheated shavings, development of the moulds results in a diminution of most of the dosed compounds : dry extract, ellagitanins, ellagic acid, sugars and volatile phenols. The action of heat erases differences previously observed in the sugars, volatile phenols and ellagic acid. However, we still notice a reduction, related to fungi action of the amounts of dry extract, ellagitanins, gallic acid and eugenol. The amounts of aromatic aldehydes including vanillin are not affected by the development of micro-organisms. A few shavings are studied separately, under the transmission electron microscope. These observations do not show any enzymatic degradation of the wood's cell walls. Sensorial analysis of the extracts does not reveal any important differences between extracts coming from wood shavings and the blank. Under practical conditions, where fungi biomass is much less than that obtained from shavings, the fungi's contribution towards final sensorial qualities of the wood, is therefore most probably negligible.

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