THE INFLUENCE OF BRETTANOMYCES DEKHERA SP YEASTS AND LACTIC-ACID BACTERIA ON THE ETHYLPHENOL CONTENT OF RED WINES/

The ability of various lactic acid bacteria isolated from wine to synt hesize volatile phenols from trans p-coumaric and ferulic acid was stu died in a model medium and compared with that of Saccharomyces cerevis iae and Dekkera intermedia. Quantitative analysis of the produced viny lphenols and ethylphenols showed that some strains of Lactobacillus br evis and Pediococcus pentosaceus were capable of decarboxylating p-cou maric acid to form 4-vinylphenol as actively as S. cerevisiae, whereas the same bacteria had a much less marked effect on ferulic acid. The other bacteria, Leuconostoc oenos in particular, only synthesize very small quantities of vinylphenols. Apart from Lactobacillus plantarum, none of the other lactic acid bacteria studied released any significan t quantities of ethylphenols during culture. However, the quantities o f ethylphenols produced by L. plantarum were still very small compared to those formed by D. intermedia and have no negative impact whatsoev er on the wine's aroma. The influence of lactic acid bacteria on the v olatile phenol content of wine is, therefore, very restricted. These f indings confirm that Brettanomyces/Dekkera are responsible for the dev elopment of a phenolic character in red wines. These yeasts multiply b y fermenting the small quantities of residual sugars (glucose, fructos e, galactose, and trehalose) in the wine. The fermentation of barely 2 75 mg/L of sugars, much less than the normal residual sugar level of n ew red wine at the end of the usual fermentation process, is sufficien t to synthesize an excessive quantity of ethylphenols with alteration of the aromatic quality of the wine.