Abstract
Non-Saccharomyces yeast plays an important role in the initial stages of a wild ferment, as they are found in higher abundance in the vineyard than Saccharomyces cerevisiae. As such, there has been a focus in recent years to isolate these yeast species and characterize their effect on wine fermentation and subsequent aroma. This effect on wine aroma is often species and strain dependent, as the enzymatic profile of each yeast will determine which aroma compounds are formed as secondary metabolites. Semi-fermentative yeast, such as Hanseniaspora spp., Candida spp. and Metschnikowia pulcherrima, are commonly in high abundance in fresh grape must and have diverse enzymatic profiles, however they show a weak tolerance to ethanol, limiting their impact to the initial stages of fermentation. Fully fermentative non-Saccharomyces yeast, characterized by high ethanol tolerance, are often found at low abundance in fresh grape must, similar to Saccharomyces cerevisiae. Their ability to influence the aroma profile of wine remains high, however, due to their presence into the final stages of fermentation. Some fermentative yeasts also have unique oenological properties, such as Lanchancea thermotolerans and Schizosaccharomyces pombe, highlighting the potential of these yeast as inoculants for specific wine styles.
Highlights
For thousands of years, throughout the history of winemaking, fermentation occurred naturally without an understanding of how it worked and the microorganisms involved [1]
The development of primary and secondary aromas in wine is a key role of yeasts during fermentation and research suggests that non-Saccharomyces yeasts produce a wider range of volatile aroma compounds than S. cerevisiae
This is because each species of yeast encodes for different concentrations of extracellular enzymes and these will have distinct effects on the aroma profile of a wine
Summary
Throughout the history of winemaking, fermentation occurred naturally without an understanding of how it worked and the microorganisms involved [1]. To avoid the effect of the non-Saccharomyces yeasts, the grape must is quickly inoculated with a large culture of S. cerevisiae [7] This allows the resulting ferment to have a much higher chance of avoiding any negative issues. Proponents of natural wine, believe this moves wine away from a natural product into an industrial one and by allowing the indigenous yeasts to perform fermentation you retain the traditional flavors and aromas of the wine [2]. This is due to two reasons: Firstly, non-Saccharomyces yeasts have been shown to produce a greater range of volatile metabolites during fermentation than S. cerevisiae. The concept of terroir suggests that the environment in which the grapes are grown leaves an aromatic fingerprint on the wine that is unique, and it is suggested that this effect extends to the regional yeasts that perform the fermentation
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