The origin of ethylphenols in wines

TLDR

Ethylphenols, aromatic compounds produced by Brettanomyces/Dekkera yeast acting on hydroxycinnamic acids, give red wines characteristic phenolic, animal, and stable off‑odors. Brettanomyces/Dekkera synthesises ethylphenols via a two‑step enzymatic pathway: cinnamate decarboxylase converts cinnamic acids to vinylphenols, then vinylphenol reductase reduces them to ethylphenols. The study shows that high ethylphenol levels arise during wine ageing after fermentation, occur more often than the classic mousy‑taint, and that Brettanomyces/Dekkera’s cinnamate decarboxylase is resistant to wine polyphenols and has distinct substrate specificity compared to Saccharomyces cerevisiae.

Abstract

Abstract Ethylphenols are important aromatic compounds of red wines. These compounds are formed in wines by some yeast species belonging to the genus Brettanomyces/Dekkera 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 Brettanomyces/Dekkera 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 Brettanomyces/Dekkera 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 Brettanomyces/Dekkera is not inhibited by the polyphenolic compounds of red wines (procyanidins and catechins) while these compounds do inhibit the CD activity of Saccharomyces cerevisiae. On the other hand, the substrate specificities of the CD activities of Brettanomyces/Dekkera and Saccharomyces are different.