Non-Saccharomyces yeasts and wine ine

Abstract

Wine fermentation is a complex bioprocess involving various microorganisms, especially yeasts and lactic acid bacteria, where yeasts play a prominent role. Of all the microorganisms involved, Saccharomyces cerevisiae yeast is the key player and is responsible for alcoholic fermentation and largely for flavour formation. It has been established that in spontaneous fermentation wine is not purely the result of biotransformation of grape musts by a single species or a single strain of yeasts and besides Saccharomyces yeasts, the indigenous, weakly fermentative non-Saccharomyces yeasts also impact on wine quality. Compared to the wines fermented with a single Saccharomyces yeast strain, spontaneous fermentation adds complexity of flavour and stylistic distinction. The predominant species of non-Saccharomyces yeasts associated with spontaneous wine fermentation include those yeasts from the genera Hanseniaspora, Candida, Kloeckera, Pichia, Zygosaccharomyces, Schizosaccharomyces, Torulaspora, Metschnikowia, Brettanomyes, Saccharomycodes and Williopsis. Non-Saccharomyces yeasts were originally associated with production of off-flavour and wine spoilage. Nonetheless, non-Saccharomyces yeasts can produce secondary metabolites that positively contribute to the final organoleptic properties of wines (e.g. esters) as well as excrete enzymes (e.g. pectinases, glucanases and β-glucosidases) which can affect wine flavour upon bioconversion of non-volatile precursors into desirable aroma compounds such as oxygenated terpenes (citronellol, linalool, geraniol, etc.). Saccharomyces yeast is still essential to complete wine fermentation due to the low stress-tolerant ability of non-Saccharomyces yeasts. Fermentation of a mixed-culture of non-Saccharomyces andSaccharomycescerevisiae yeasts takes advantage of the flavour-enhancing potential of the former and the ethanol-producing ability of the latter. Early death of non-Saccharomyces yeasts is an issue in mixed-culture fermentation due to several factors: competition for sugar uptake, space confinement, SO2 concentration, oxygen availability, nutrient limitation, presence of toxic compounds, cell-cell contact and quorum sensing. The potential of non-Saccharomyces yeasts in winemaking is still untapped. In order to exploit the potential benefits of non-Saccharomycesyeasts in wine fermentation and to minimize their negative impact on wine flavour (e.g. spoilage and off-flavourformation), more research should be conducted to better understand the biodiversity, physiology, metabolism, genetics, molecular pathways and cell biology of non-Saccharomyces yeasts. © 2012 Nova Science Publishers, Inc. All rights reserved.