## 4 Discussion  
The grapes, the must and the wine environment are complex microecosystems that are characterized by multiple interactions, which can be detrimental for the quality of the final product. Inevitably, the environmental changes that occur throughout the winemaking process shapes the microbial community not only in terms of species/strains that are  
Figure 4: Biplot of the principal component analysis (PCI vs. PC2) for descriptive sensory analysis of Sauvignon blanc wines fermented with monocultures of _S. cerevisiae_ and _S. pastorianus_ (Sc1, Sc2 and Sp2) as well as with mixed cultures of both species in different inoculation ratio. present, but also on the metabolites' production [21; 22]. The feasibility of inoculating _S. cerevisiae_ with a non-_Saccharomyces_ yeast (e.g., _Torulaspora delbrueckii_) in order to partially mimic the indigenous microbiota composition and promote an aromatic typicity and complexity has been widely explored [23; 24; 25]. Nevertheless, the species compatibility is not always taken for granted as antagonistic mechanisms may be developed with a controversial impact on the wine's fermentability and the quality characteristics. The objective of our study was to evaluate the compatibility of the strains belonging to the _Saccharomyces_ genus as fermentation starters to promote the wine aromatic typicity. Thus, two strains of _S. cerevisiae_ and one strain of _S. pastorianus_ were chosen to be inoculated in different inoculation ratios in the Sauvignon blanc must. According to our results, the indigenous population of non-_Saccharomyces_ yeasts showed a different growth behavior according to the inoculation scheme, and especially, the added strain of _S. cerevisiae_. The presence of Sc1 in any inoculum proportion decreased their population by approximately 2 log CFU/mL, while the presence of Sc2 kept a constant cell concentration. Additionally, the presence of _S. pastorianus_ affected neither the indigenous population nor the added _S. cerevisiae_ strain. During the vinicification process, the niche construction is evolving and inevitably, a selection pressure is created for the microorganisms [2; 4; 26]. The way in which these mechanisms may impact the inter and intra species physiology depends on many factors that are more or less known [4; 25; 27]. In our case, Sp2 and Sc1 produced significant high amounts of SO2, which is a strong antimicrobial agent, especially against the non-_Saccharomyces_ yeast; therefore, the control of the wild yeast population is justified. _Saccharomyces pastorianus_ is a species that is characterized by low acetic acid production under winemaking conditions, but at the same time its fermentation capacity cannot compete with the respective one of _S. cerevisiae_[7]. Nevertheless, in our present work we proposed that the co-inoculation of _S. pastorianus_ with _S. cerevisiae_ in any ratio can lead to lower acetic acid levels without negatively affecting the fermentation kinetics or the other oenological characteristics. As acetic acid is correlated with volatile acidity, its concentration is critical for wine quality. The yeast cells produce acetic acid during the alcoholic fermentation and the formation level of it depends on many factors such as the yeast strain, the oxygen level, the osmotic stress or the nitrogen content [5; 28; 29]. Under oenological conditions, through the aspect of species competition, the production of acetic acid may act as an antimicrobial factor with a negative effect on the yeast fermentative performance [28; 30]. This phenomenon is more frequent when non-_Saccharomyces_ yeasts are used in mixed cultures with _S. cerevisiae_ or when spontaneous fermentations take place [31; 32; 33]. Interestingly, some strains of _S. cerevisiae_ are capable of metabolize acetic acid under limited aerobic conditions, thereby giving an interesting technological trait [29]. In our case, the two tested species, _S. pastorianus_ and _S.