## 4 Discussion  
Enhancing aromatic complexity without altering varietal typicity is the key to effectively addressing the recent consumer trends toward new sensorial challenges. The strategy that has been employed for that purpose includes the utilization of yeast strains that unfold the typical varietal aromas and at the same time supplement them through the production of fermentation aromas. Thus, novel combinations are created, at least from the varietal typicity perspective. _S. pastorianus_ is not that common in winemaking while _S. bayanus_ is used more frequently, however, usually for difficult fermentations, i.e., for high levels of sugar musts or stuck fermentations; however, they have provided very interesting results regarding the alcoholic fermentation of Sauvignon Blanc must, especially under co-inoculation mode [27]. The aim of the present study was to expand our knowledge of the interactions between two strains of the aforementioned species and their effect on the sensorial quality of Sauvignon Blanc wine. Thus, the chemical composition and the sensorial properties of wines made by the co-culture of these strains at different ratios were evaluated and compared with the ones made by each strain separately and through spontaneous fermentation. Controlled fermentation through the utilization of suitable strains is the strategy employed in order to obtain reproducible results. In the case of alcoholic fermentation, strains belonging to the _Saccharomyces_ genus are employed for ethanol production, and strains belonging to other genera, such as _HanseniSpora_, _Metschnikowia_, _Issatchenkia_, _Pichia_, _Schizosaccharomyces_, _Torulaspora_ and _Lachaneca_, for the production of aroma compounds [23; 30; 31; 32; 33; 34; 35; 36]. Spontaneously fermented wines are usually characterized by higher sensorial complexity and richer body, which has been attributed to the larger variety of metabolites produced by the larger yeast consortium that contributes to alcoholic fermentation [16; 37; 38]. However, this consortium is uncontrolled, and, therefore, the outcome of the fermentation is unpredictable. Thus, spontaneously fermented wines may be characterized as highly acceptable [39; 40], or, as in the present study, sensorially unsatisfactory [41]. Additionally, according to our results, the volatile and sensory profiles of the spontaneously fermented wines were well distinguished compared to the inoculated ones. It seems that the dominance of non-_Saccharomyces_ yeast after 48h of alcoholic fermentation clearly has an impact on the final produced wines [42]. Figure 4: Heatmap analysis representation corresponding to Sauvignon Blanc wine sensory evaluation fermented under different inoculation schemes. The relative content of each sensory attribute is illustrated through a color scale (from dark blue, minimum, to dark red, maximum). The asterisk denotes a statistically significant difference (\(p<0.05\)) between each attribute and the fermentation-shence. Even if the impact of non-_Saccharomyces_ yeast in wine has been well documented in the literature [43; 44], the prediction of their intra- and inter-species interaction along the winemaking process is not yet established. The main obstacle of both spontaneous and co-inoculation strategies in wine production is the compatibility of the microbial strains, in terms of population growth and metabolite production. The antagonistic interactions that possibly develop may have a negative impact on wine quality [45; 46; 47]. Regarding the relationship between the _S. bayanus_ and the _S. pasorianus_ strains used in the present study, good compatibility was observed between the strains since no negative oenological attributes were detected. In terms of coexistence during fermentation, _S. bayanus_ seems to grow more efficiently in the must environment, since it managed to grow at populations equal to or higher than the respective population of _S. pasorianus_, even though it was inoculated at a lower initial population.