# Biotechnological Approaches to Lowering the Ethanol Yield during Wine Fermentation
## 3 Alternative Wine Yeast Species  
Microbial ecology studies of grape juice and wine fermentation clearly indicate that, most often, _S. cerevisiae_ is a minor species at the beginning of the fermentation process. In contrast, it is almost invariably the dominant one at the end of spontaneous fermentations. Therefore, this species is considered particularly well adapted to the process, and has been selected for use in inoculated fermentations. The other yeast species present during the initial stages of fermentation were traditionally considered to be spoilage microorganisms, and therefore undesirable. Over time, after inoculation with _S. cerevisiae_ became common practice, non-_Saccharomyces_ wine yeast species have been found to harbour interesting characteristics, such as their contribution to the aroma and complexity of the wine, and their ability as microbiological control agents [34]. Several commercial strains of non-_Saccharomyces_ yeast are currently available for use in wine fermentation, including _Torulaspora delbrueckii_, _Lachanea thermotolerans_ and _Metschnikowia pulcherrima_, among the most common yeast species [35]. In addition to their features related to the sensorial quality of wines, one potentially interesting feature of some non-_Saccharomyces_ species is their lower ethanol yield compared to _S. cerevisiae_. However, only during the last decade has the possibility of using alternative yeast species to reduce alcohol content been considered [36]. A summary of the results described below, using different non-_Saccharomyces_ yeast species to obtain lower alcohol wines, is shown in Table 1.  
Figure 1: Diagram of the alcoholic fermentation pathway with indications of the steps affected by the different genetic modifications assayed to lower ethanol yields. References in black: genetic engineering. References in yellow: adaptive evolution. Metabolites outside of the central ethanol fermentation pathway are indicated in purple. The cryophilic species _Saccharomyces uvarum_ has been described as a low ethanol, low acetate, and high glycerol producer yeast [37; 59; 60]. In experimental fermentations, the ethanol contents of wines produced with two strains of _S. uvarum_ were 0.5 and 0.3% ABV lower than _S. cerevisiae_ wine, and their hybrids showed ethanol contents which were intermediate between the parent species [37]. An important reduction (1.7% ABV) was obtained with a strain of _S uvarum_ in Merlot wine, but it showed predominantly negative attributes in a sensory analysis, with aromas of meat and barnyard [38]. Another cryophilic species, _Saccharomyces kudiavzevii_, has been described as a high glycerol producer [61]. Although _S. kudiavzevii_ is not found in winemaking, _S. cerevisiae_\(\times\)_S. kudiavzevii_ hybrids are often isolated from cold-climate wine environments. However, the ethanol yield of these hybrids has been found to be higher than that of _S. cerevisiae_[62]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Single Species** & **Sugar Content** & **Conditions** & **Sensory** & **Time for S.** & **Ethanol** & \\  & **(g/L)** & **Analysis**\({}^{c}\) & & _cerevisiae_ & **Reduction** & **Reference** \\ \hline _Saccharomyces uvarum_ & 171 1 & standard & Negative & No. Pure culture & 0.5 & [37] \\  & 240 2 & standard & Negative\({}^{c}\) & No.