# Biotechnological Approaches to Lowering the Ethanol Yield during Wine Fermentation
## 3 Alternative Wine Yeast Species
The authors highlight the variability in the rate and extent of sugar utilisation between strains of the same species, except for _S. cerevisiae_ species, and the differences in aroma compounds produced by strains affecting the wine aroma. Wines made with selected strains of _Hansenispora quantiae_, _Hansenispora uwarum_, and _Pichia kudriavzevii_, in sequential inoculation with _S. cerevisiae_, contained between 0.4 and 1.5% ABV less than the control wines. There are currently several strains of _T. delbrueckii_ for winemaking in the market which have been selected for their contribution to the aromatic complexity of wine. Regarding the ability to lower the alcohol content, there was a 0.5% _v/v_ reduction in the ethanol content compared to the _S. cerevisiae_ control wine [52]. [PERSON] et al. (2019) [53] studied the effectiveness of one commercial strain of _T. delbrueckii_ and one strain of _M. pulcherrina_, in co-inoculation with _S. cerevisiae_ and/or _S. bayanus_. In pasteurised must, a reduction of 0.9% (_v_/_v_) in ethanol concentration was achieved with _Metschnikowia_ and 0.5% with _Torusspona_, but this effect was lost in natural must, probably due to the low dominance of the selected strains. _L. thermotolerans_ has also been introduced in the market because its positive effects on wine aroma, total acidity, and volatile acidity [68]. Wines obtained with the sequential inoculation of _L. thermotolerans_ and _S. cerevisiae_ contained 1.2% less ethanol than the control wine, but suffered a decrement in aroma quality [55]. Some authors are also exploring yeast cell immobilization to improve effectiveness and process control (Table 1). [PERSON] et al. (2016) [56] studied the use of immobilised alternative yeasts, together with free _S. cerevisiae_ in sequential inoculation. Using _Starmerella bombicola_, _H. urarum_, _Hansenispora osmophila_ and _M. pulcherrina_, ethanol reduction valuesfrom 1.0 to 1.6% (\(v/v\)) were achieved. Changes in the volatile compounds were also observed. It was predicted that these could potentially affect the sensory properties of the wines, either positively or negatively, depending on the case, but the study did not include a sensory evaluation. Finally, the authors indicated that this technology makes the process more expensive. [PERSON] et al. (2018) [58] obtained a 1.7-2.4% reduction of ethanol levels with immobilized cells of _Schizosacharomyces japonicus_ in co-inoculation and sequential inoculation with free _S. cerevisiae_. The levels of acetoin, ethyl acetate, and acetate esters were higher in both wines, and acetic acid and glycerol were higher in wine made by sequential inoculation. Several of the studies described above show some promise for non-_Saccharomyces_ yeast used in sequential or co-inoculation with _S. cerevisiae_ for the reduction of ethanol yields during wine fermentation, and hence the alcohol content of wines. However, even under laboratory controlled experimental conditions, the reduction values were generally moderate (Table 1), and difficulties associated to scale-up were often reported. Fairly different reduction values are published by different laboratories, which is not surprising because the authors did not follow standardized conditions (the optimization of fermentation conditions is usually a secondary objective of their work), and different strains were used in each case. According to the available information, when developing protocols aiming at alcohol level reduction, attention should also be paid to the impact of strains and fermentation conditions on the sensory properties of the wines. In addition, the use of non-_Saccharomyces_ species for alcohol reduction faces technological challenges common to other oenological applications of these strains. These include difficulties for the industrial production of most of them as active dry yeast, a generally low tolerance to sulphiting agents, low imposition, or considerations about compatibility with _S.