# Aromatic Potential of Diverse Non-Conventional Yeast Species for Winemaking and Brewing
## 3 Results and Discussion
### Microwine
#### 3.1.1 Fermentation Performance  
Multifactorial ANOVA shows that non-conventional strain and type of culture, pure or mixed, were significant factors determining the residual sugar amount. However, just the type of culture was significantly influencing ethanol yield, indicating that ethanol synthesis was similar among the non-conventional yeasts employed in this study. Residual sugars and ethanol production of the resulting microwines are presented in Table 3.  
One-way ANOVA points out that, in general, fermentations carried out by pure cultures of non-conventional yeasts left significantly higher amounts of residual sugars and produced lower quantities of ethanol compared to their corresponding mixed cultures and reference _S. cerevisiae_ Lalvin T73. Ethanol was not even detected in case of _Starmen caribaea_ CBS 7692 and _Barmettozyna california_ CBS 8860 as practically no fermentation of the sugars occurred. One exception to this pattern was _Wickerhamomyces subpelliculosus_ CBS 5552, which showed a fermentation performance as good as the reference strain even when used as a pure culture, leaving hardly any residual sugars and producing high ethanol levels. Its fermentation efficiency was in accordance with [16], who observed similar ethanol production by this strain compared to _S. cerevisiae_ baker's yeast when bread fermentations were carried out and may indicate that this strain presented an intense Crabtree effect similar to _S. cerevisiae._  
The difference in ethanol production between pure and mixed cultures can be explained by the fact that it has been demonstrated that yeast in mixed cultures do not simply coexist, but rather interact, and as a result, oenological traits can be modulated [17]. The finding that single cultures of non-_Saccharomyces_ yeasts are, in general, poor fermenters and sensitive to ethanol is in accordance to several authors [17; 18; 19]. _S. cerevisiae,_ as consequence of Crabtree effect, prioritises fermentative metabolism over aerobic respiration when sugar levels are higher than 10 g/L. Nevertheless, many non-_Saccharomyces_ yeasts do not show this effect and are able to grow using oxygen regardless of sugar concentration and thus, divert carbon into other metabolites, which reduces ethanol production [20]. In this way, fermentation performance improves when non-_Saccharomyces_ yeasts are together with _S. cerevisiae,_ with some exceptions. For instance, [PERSON] et al. [3] presented _Kazchstania gamospora_ CBS 10400, the strain employed in this study, as Crabtree positive, observing a fermentation performance similar to _S. cerevisiae in terms of residual sugars and ethanol yield when employed in sequential inoculation together to _S. cerevisiae._ In our study, CBS 10400 when used in mixed fermentation resulted in less residual sugars and much higher ethanol content, approaching that produced by _S. cerevisiae._  
On the other hand, the limited ethanol synthesis can also be considered an advantage for the wine sensory profile, since excessive ethanol amounts can increase the perception of bitterness and astringency and mask some volatile compounds [20]. Furthermore, this approach leads to the development of healthier wines and has been proposed as a strategy for counteracting climatic change and the resulting ethanol increase in wines [20]. Another interesting aspect is that it has been demonstrated that non-_Saccharomyces_ strains that show poor efficiency in fermenting sugars may produce higher glycerol quantities, which is a highly desirable trait in wines, especially in red [11]. On the other hand, mixed cultures were similar to the reference strain in terms of residual sugars and ethanol yield. _Torulspora microellipsoides_ CBS 6641 in mixed culture even produced significantly more ethanol than the reference strain, being two-fold that produced in their corresponding pure culture. However, previous literature indicates that this strain produced low ethanol levels in sequential