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International competition within the wine market, consumer demands for newer styles of wines and increasing concerns about the environmental sustainability of wine production are providing new challenges for innovation in wine fermentation. Within the total production chain, the alcoholic fermentation of grape juice by yeasts is a key process where winemakers can creatively engineer wine character and value through better yeast management and, thereby, strategically tailor wines to a changing market. This review considers the importance of yeast ecology and yeast metabolic reactions in determining wine quality, and then discusses new directions for exploiting yeasts in wine fermentation. It covers criteria for selecting and developing new commercial strains, the possibilities of using yeasts other than those in the genus of Saccharomyces, the prospects for mixed culture fermentations and explores the possibilities for high cell density, continuous fermentations.

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The performance of denaturing gradient gel electrophoresis (DGGE) for analysing yeasts associated with wine grapes was compared with cultural isolation on malt extract agar (MEA). After optimisation of PCR and electrophoretic conditions, the lower limit of yeast detection by PCR-DGGE was 10(2) cfuml(-1), although this value was affected by culture age and the relative populations of the species in mixed culture. In mixed yeast populations, PCR-DGGE detected species present at 10-100-fold less than other species but not when the ratio exceeded 100-fold. Aureobasidium pullulans was the main species isolated from immature, mature, and both damaged and undamaged grapes. It was not detected by PCR-DGGE when present at populations less than 10(3) cfug(-1). When approaching maturity, damaged grapes gave a predominance of Metschnikowia and Hanseniaspora species (10(5)-10(7) cfug(-1)), all detectable using PCR-DGGE. However, various species of Rhodotorula, Rhodosporidium and Cryptococcus were not detected by this method, even when populations were as high as 10(4) cfug(-1). PCR -DGGE was less sensitive than culture on MEA for determining the yeast ecology of grapes and could not reliably detect species present at populations less than 10(4) cfug(-1). However, this method detected a greater diversity of species than agar plating.