Ethylphenols are important aromatic compounds of red wines. These compounds are formed in wines by some yeast species belonging to the genus BrettanomyceslDekkera in the presence of hydroxycinnamic acids. These volatile phenols are responsible for the 'phenolic', animal' and 'stable' off-odours found in certain red wines. The results presented show that the synthesis of the high quantities of ethylphenols found in the 'phenolic' red wines can occur during the ageing of wines having normally completed their alcoholic and malo-lactic fermentations. This olfactory fault caused by BrettanomyceslDekkera is found more frequently than the classical 'mousy-taint' attributed to this yeast genus. In addition, the study of the mechanisms of biosynthesis of ethylphenols by BrettanomyceslDekkera has shown the sequential activities of two enzymes. The first, is a cinnamate decarboxylase (CD), which assures the transformation of certain cinnamic acids into the correspondent vinylphenols; the second is a vinylphenol reductase, which catalyses the reduction of vinylphenols into ethylphenols. The CD activity of BretfanornyceslDekkera is not inhibited by the polyphenolic compounds of red wines (procyanidins and catechins) while these compounds do inhibit the CD activity of Saccharomyces cereuisiue. On the other hand, the substrate specificities of the CD activities of BrettanomyceslDekkera and Saccharomyces are different.

<p style="text-align: justify;">L'élevage des vins en barriques modifie profondément leur expression aromatique.</p><p style="text-align: justify;">L'étude par chromatographie en phase gazeuse et spectrométrie de masse permet d'identifier plusieurs substances volatiles appartenant à la fraction phénolique des arômes.</p><p style="text-align: justify;">Les vins rouges présentent naturellement une composition complexe en phénols volatils alors que celle des vins blancs est plus simple. L'élevage sous bois entraîne une augmentation notable des phénols déjà présents ainsi que l'apparition de molécules spécifiques au bois dechêne brûlé.</p><p style="text-align: justify;">L'interaction des levures et des bactéries avec le bois est mise en évidence.</p><p style="text-align: justify;">Les vins rouges se caractérisent par une présence parfois abondante d'éthyl phénols, les vins blancs qui ne subissent pas la fermentation malolactique s'en différencient par l'abondancede vinyl phénols.</p><p style="text-align: justify;">L'étude sensorielle de chaque substance permet de démontrer le rôle négligeable de certaines : furfural, méthyl-5-furfural, alcool furfurylique et le rôle exceptionnel joué par d'autres : cis et trans β-méthyl-γ-octalactone, vanilline et dans certains cas éthyl-4-phénol et éthyl-4-gaïacol.</p><p style="text-align: justify;">+++</p><p style="text-align: justify;">Wood storage of wines changes profondly their aromatic expression.</p><p style="text-align: justify;">Several volatile substances from wines and oak woods phenolic fraction of aroma are identified by gas chromatography and mass spectrometry. Wood storage increases natural phenols concentration. Simultaneously specific burned wood molecules appear.</p><p style="text-align: justify;">Yeast and bacterial interaction with wood is demonstrated. Ethyl phenols are characteristic of red wines and vinyl phenols of white wines without malolactic fermentation.</p><p style="text-align: justify;">The sensorial analysis of each substance demonstrates the negligible intervention in wine aroma of furfural, 5-methyl-furfural, and furfuryl alcohol, and the important participation of cis and trans β-methyl-γ-octalactone, vanilin 4-ethyl-phenol and 4-ethyl gaïacol.</p>

are natural constituents of wine and can play a role in wine aroma. However, only white wines contain important quantities of these volatile substances which, beyond a certain concentration (limit threshold = 725 pg litre-l of 4-vinylguaiacol+ 4-vinylphenol (1 : l)), can be responsible for a depreciating 'phenolic' or 'pharmaceutic' characteristic. Succhuromyces cerevisiae possesses a type-(E) enzymic activity, substituted cinnamate carboxy-lyase (SCD), which is capable of transforming, by non-oxidative decarboxylation, the phenolic acids in the must, ( E ) p-coumaric and ( E ) ferulic acids, into corresponding vinylphenols. This endocellular activity is constitutive, it is only expressed during alcoholic fermentation and with a variable intensity depending on the yeast strain. Furthermore, the enzyme is rapidly inhibited by catechic tannins, which explains why, in comparison with white wines, red and rosi wines contain low levels of vinylphenols despite having more precursors. A yeast strain with a weak SCD activity has been selected and its use in vinification should eliminate the appearance of the phenolic taint in white wines coming from grapes rich in decarboxylable hydroxycinnamic acids.