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Red wine was made from the same batch of Cabernet Sauvignon grapes but with two different yeasts, Saccharomyces cerevisiae (SC) or Saccharomyces bayanus (SB). The colour properties and pigment profiles of SC and SB wines were compared at 8 days and 387 days after yeast inoculation. Grape anthocyanin concentration was found to be lower in SB wines than in SC wines at day 8 and 387, but SB wine exhibited greater wine colour density, a* and b*. The anthocyanin concentration did not correlate with wine colour density. The levels of pigmented polymers and SO2 non-bleachable pigments were found to be higher in SB wine at day 387, demonstrating that the formation of stable pyranoanthocyanins and pigmented polymers was enhanced by SB yeast. Electrospray mass spectrometry was used for the compositional analysis of pyranoanthocyanins, and direct and ethyl-bridged linked condensation dimers of malvidin 3-O-glucoside (MvG) with flavanols (catechin or epicatechin). The data demonstrated that the formation of acetaldehyde-mediated pigments was enhanced by the use of the SB yeast. The compositional analysis suggested that the differences in colour properties and pigment profiles of SC and SB wines were largely due to the greater production of acetaldehyde-mediated pigments by the use of SB yeast.

The use of yeasts other than Saccharomyces cerevisiae to produce wines with novel aroma and flavour profiles is gaining increased attention. The present study is concerned with the sensory impact on wine of fermentation with two selected Saccharomyces bayanus strains. The S. bayanus strains AWRI 1176 and AWRI 1375 were compared to S. cerevisiae strain AWRI 838 for their ability to affect the aroma profile and chemical composition of Chardonnay wine. Wines that were made with the S. bayanus strains contained more glycerol, succinic acid, acetaldehyde and SO 2 than reference wines made with the S. cerevisiae wine yeast, but less acetic acid, malic acid and ethyl acetate. There were significant differences in the aroma profile of wines made with each yeast, as quantified by formal sensory descriptive analysis. Wines made with S. cerevisiae AWRI 838 were rated highly in the attributes 'estery', 'pineapple', 'peach' and 'citrus'. Wines made with S. bayanus AWRI 1176 were rated lower than AWRI 838 in each of these attributes, but higher in the attributes 'cooked orange peel', 'yeasty', 'nutty' and 'aldehyde'. The aroma profile of wine made using AWRI 1375 was different from that of wine made with the other yeasts, showing intermediate scores for the 'estery', 'citrus', 'nutty' and 'aldehyde' attributes, and no significant difference from the AWRI 838 strain in the attributes 'pineapple' and 'peach'. These results demonstrate that, in addition to producing wine which has a different chemical composition, S. bayanus strains can produce a different sensory profile in wine when compared to a widely used S. cerevisiae wine yeast.

Glycerol is a major fermentation product of Saccharomyces cerevisiae that contributes to the sensory character of wine. Diverting sugar to glycerol overproduction and away from ethanol production by overexpressing the glycerol 3-phosphate dehydrogenase gene,GPD2, caused S. cerevisiae to produce more than twice as much acetic acid as the wild-type strain (S288C background) in anaerobic cell culture. Deletion of the aldehyde dehydrogenase gene, ALD6, in wild-type and GPD2 overexpressing strains (GPD2-OP) decreased acetic acid production by three- and four-fold, respectively. In conjunction with reduced acetic acid production, the GPD2-OP ald6Δ strain produced more glycerol and less ethanol than the wild-type. The growth rate and fermentation rate were similar for the modified and wild-type strains, although the fermentation rate for the GPD2ald6Δ strain was slightly less than that of the other strains from 24 h onwards. Analysis of the metabolome of the mutants revealed that genetic modification affected the production of some secondary metabolites of fermentation, including acids, esters, aldehydes and higher alcohols, many of which are flavour-active in wine. Modification of GPD2 and ALD6 expression represents an effective strategy to increase the glycerol and decrease the ethanol concentration during fermentation, and alters the chemical composition of the medium such that, potentially, novel flavour diversity is possible. The implications for the use of these modifications in commercial wine production require further investigation in wine yeast strains. Copyright © 2002 John Wiley & Sons, Ltd.