## 3 Results and Discussion  
### Fermentation Kinetics and Microbiota Dynamics During Sampling Stages  
The yeast strain Levulia Agglo is a _S. cerevisiae_ r._ oviformis_ with a neutral killer phenotype (it does not produce any killer toxins itself and is resistant to the killer toxins produced by others) [28]. The use of this strain is recommended for industrial second fermentations or _prise de mousse_ in sparkling wine production, because its agglomerating property reduces the time of the remuage phase from 4-6 weeks to 1-2 weeks compared to standard strains [29]. This tendency of the cells to cohere and adhere to each other facilitates their sedimentation and the wine clarification process. However, yeast strainswith this property are not preferred by winemakers in still wine production because they settle quickly, risking incomplete fermentation, off-flavors, and microbial instability. This yeast has other desirable characteristics for industrial winemaking, suitable for aging on the lees due to its easy autolysis, predictable kinetic and complete fermentation at moderate temperatures (13-20 \({}^{\circ}\)C), and medium-high nitrogen demand, with an ethanol tolerance of 13.8% \(v/v\), according to the manufacturer's specifications. Figure 1 shows the fermentation kinetics over 17 days for the four conditions studied. The density values decreased from 1095 to 995 g L\({}^{-1}\) after 17 days in all fermentations, showing similar trends between them, with a gradual decrease in density starting around day 6 in all conditions and converging towards approximately 995 g L\({}^{-1}\) by day 16. However, the fermentation kinetics of WY were faster than those of AGGLO, which could be explained by the slower growth rate of flocculent yeasts compared to other yeast strains [30]. Cells within the floc have a smaller surface area, which limits nutrient diffusion and slows growth. In contrast, the AGGLO + Act condition experienced a faster fermentation process between days 6 and 12. The WY + Act condition did not show this trend and instead showed slower fermentation kinetics compared to the other conditions. The faster fermentation kinetics in AGGLO + Act suggest a synergistic effect between the AGGLO yeast and the tested additive, increasing fermentation efficiency. By day 17 of fermentation, all conditions reached similar density levels with only slight differences in the timing and rate of density decline. After this fermentation period, the wines were allowed to settle at 10 \({}^{\circ}\)C for 10 days, and the volume of the sediment at the bottom of the glass cylinders was measured. The volume of lees measured for the AGGLO wines was 7.7% of the initial wine volume, and for the AGGLO + Act wines it was lower (7.1%). For WY and WY + Act wines, the volume of lees was 8.3% and 7.1% of the total wine volume, respectively. Therefore, the tested activator caused a reduction of 0.6 and 1.2% in the volume of lees, which reduces the loss of wine volume from the cell. Figure 1: Evolution of alcoholic fermentation. The left axis (lines) shows the density values (g L\({}^{-1}\)) throughout the fermentation days. The right axis (bars) shows the total viable number of cells (colony-forming units—CFUs) in the WLN medium on days 0, 4, 7, and 17 of the fermentation. Statistical differences at the \(p\leq\) 0.05 level are indicated by different letters. Abbreviation of wines obtained by fermentation with WY: wild yeast; WY + Act: the same with the addition of an activator; AGGLO: Levulia® AGGLO yeast; AGGLO + Act: the same added with the activator. The number of viable cells was monitored in all conditions at three different stages of the fermentation process. The microbiological analysis of the uninoculated grape must (D0) revealed a low viable cell count, with a density of 10\({}^{3}\) CFU mL\({}^{-1}\). By day 4, a significant increase in viable cells was observed, especially in the WY + Act condition, reaching 200 \(\times\) 10\({}^{6}\) CFU mL\({}^{-1}\), compared to the other fermentations.