Distribution of phenolic yeasts and production of phenolic off-flavors in wine fermentation

The activity of wine yeasts to decarboxylate ferulic and p-coumaric acids is one of their biological properties related to the production of phenolic off-flavors (POF) in wine-making. We examined POF productivity in 116 strains of wine yeast, 74 strains of wild yeast (Saccharomyces cerevisiae) and 23 strains of non-Saccharomyces yeast, and found that a majority of these yeasts were POF-producing strains. The frequency distribution of POF-producing strains was 81 to 95% in wine yeasts, 85 to 97% in wild yeasts and 78 to 83% in non-Saccharomyces yeasts based on the POF test with addition of ferulic and p-coumaric acids to grape juice medium. The Rhodotorula, Candida, Cryptococcus, Pichia, Hansenula, and Brettanomyces strains had high or moderate POF productivity among the 20 non-Saccharomyces species. The decomposition rate of ferulic acid correlated with POF production and the critical concentration of phenolic acid (free form) in grape must was estimated to be more than 10 mg/l. Segregation of POF phenotype and Southern blot analysis of phenolic wine yeasts suggest that POF production is controlled by the POF gene (PAD1). The results showed the frequent distribution of phenolic yeasts in the wine-making environment. These suggest the importance of controlling POF production by using wine yeast strains of low POF productivity. The grapes must be prepared by a suitable process to prevent the increase in phenolic acid content.