## 3 Results and Discussion
### Impact of Fermentation Parameters on Fermentation Time and Physicochemical Variables  
As mentioned in the general introduction of this study, both \(Sc\) and \(Lt\) have different fermentative capabilities when used in pure culture, with \(Sc\) leading to a shorter fermentation and a higher amount of ethanol, and \(Lt\) culture leading to less alcohol and a decrease in pH via lactic acid production, but with a higher fermentation time. The goal of an optimized mixed fermentation is to obtain a compromise between the properties of both yeasts. Thus, after having studied the influence of the different parameters on the population dynamics, it was necessary to study their general impact on fermentation to see how both these different population equilibria and the more direct impact of the yeast metabolism parameters chosen could modify the characteristics of the medium. The effects of incubation ratio, nitrogen content, oxygenation, and temperature on fermentation are given in Table 4.  
Fermentation took between 7 and 16 days to obtain the total consumption of sugars, depending on the conditions tested (see additional data in Figure 11 and Table 12). Thus, the choice of environmental conditions could considerably affect the resulting fermentation kinetics. The four factors studied had different impacts on fermentation time. Oxygenation seemed to lead to longer fermentation times (stand. effect 3.086), which was to be expected, given that it was shown above to favor \(Lt\) more than \(Sc\). On the contrary, an increase in the \(Sc/Lt\) ratio or in the amount of nitrogen resulted in a decrease in fermentation time (stand. effect \(-3.057\) and \(-2.384\), respectively, but with a slight significance (\(p\)-value 0.055 and 0.097, respectively)) due to their positive impact on the \(Sc\) population. An increase in temperature led to a shorter fermentation (stand. effect \(-7.122\), \(p\)-value 0.006). This very significant effect (which explained 64.8% of the variance) was certainly linked to the positive effect of temperature on the \(Sc\) population (see Section 3.1), and supported the work of [PERSON] et al. (2013) [16]. Ethanol production reached values of about 11-12% ethanol (\(v/v\)) at the end of the fermentation for all the conditions tested (see additional data in Table 12). This production was not impacted by temperature or the amount of nitrogen, but was impacted, albeit \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{2}{c}{\(Sc/Lt\) Ratio} & \multicolumn{1}{c}{Nitrogen} & \multicolumn{1}{c}{Oxygenation} & \multicolumn{1}{c}{Temperature} & \multicolumn{1}{c}{Residuals} \\ \hline \multirow{3}{*}{Fermentation time} & Stand. effect & \(-3.057\) & \(-2.384\) & \(3.086\) & \(-7.122\) & \\  & \(p\)-Value & 0.055 & 0.097 & 0.054 & \(0.006\) & \\  & Var. contrib. & 11.90\% & 7.26\% & 12.20\% & 64.80\% & 3.83\% \\ \hline Ethanol concentration (\% \(v/v\)) & Stand. effect & 2.899 & 0.402 & \(-2.857\) & 1.418 & \\  & \(p\)-Value & 0.063 & 0.715 & 0.065 & 0.251 & \\  & Var. contrib. & 38.70\% & 0.74\% & 37.50\% & 9.25\% & 13.80\% \\ \hline \multirow{3}{*}{pH} & Stand. effect & 2.575 & 1.159 & \(-0.644\) & \(-0.257\) & \\  & \(p\)-Value & 0.082 & 0.330 & 0.566 & 0.813 & \\  & Var. contrib. & 57.90\% & 11.70\% & 3.62\% & 0.58\% & 26.20\% \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Lactic acid concentration (g.L\({}^{-1}\)) \\ \end{tabular} } & Stand. effect & \(-7.32\) & \(-0.593\) & 1.809 & \(-2.034\) & \\  & \(p\)-Value & \(0.005\) & 0.595 & 0.168 & 0.135 & \\ \cline{1-1}  & Var. contrib. & \(83.30\%\) & 0.55\% & 5.08\% & 6.42\% & 4.66\% \\ \hline \end{tabular} Stand. effect = standardized effect; Var. contrib. = contribution to variance. Data are identified as statistically almost significant (0.05 \(<\)\(p\)-value \(<\) 0.1, light grey background), significant (\(p\)-value \(<\) 0.05, grey background), or very significant (\(p\)-value \(<\) 0.01, dark grey background).  
\end{table} 
Table 4: Impact of parameters on fermentation.