# Yeast Diversity during Spontaneous Fermentations and
## 3 Results and Discussion
### Viiiification Using Indigenous S. cerevisiae Strains with Differentiated Genotypes
Many studies had reported that higher levels of ethyl esters of fatty acids in wine samples followed greater accumulation of the respective fatty acid precursors [55; 56]. However, in this study, such correspondence between fatty acids and their ethyl esters was not observed (Table S5). The volatile fatty acid ethyl esters can be synthesised by _S. cerevisiae_ with participation of several esterases and ethanol acyltransferases, e.g., ETH1 and EEB1 [57]. It would therefore be interesting to test whether the indigenous yeast strains possess varied enzyme activities that might lead to different levels of fatty acid ethyl ester synthesis. Conversely, a general reduction in acetate esters was found in wines fermented with the indigenous _S. cerevisiae_ (Figure 5A). This decrease can be driven by ethyl acetate, a major component of acetate esters with the highest OAV seen in wines (Tables 2 and S5). Only NX16 and NX24 yielded ethyl acetate slightly above 150 mg/L, a level where it is usually considered as a fault rather than providing fruity aromas [57]. All tested yeast strains produced considerable amounts of higher alcohols (Table S5), and their impact on wine aroma modulation depends on the complicated wine matrix [58] and, therefore, needs further investigation. The most abundant higher alcohol in all wines was 3-methyl-1-butanol, followed by phenylethyl alcohol, in agreement with several previous studies [27; 28]. The lowest level of 3-methyl-1-butanol and phenylethyl alcohol was detected in NX23 wines, and the highest in NX4 (3-methyl-1-butanol) or NX22 wines (phenylethyl alcohol) wines (Table 2). The 15 compounds with OAV > 1 were further divided into five categories of sensory traits based on their odour characteristics, comprising sour fruit, floral, creamy, sweet fruit and green, and was used to predict their sensory characteristics. The Cabernet Sauvignon wines fermented using 11 indigenous _S. cerevisiae_ might exhibit a richer flavour, especially fruity and floral, than those produced with XR (Figure 5B). Of particular interest was the sensory simulation of NX16 wines, showing the strongest sweet fruit, creamy and sour fruit aromas whilst the green aromas were weak (Figure 5B). Figure 4: Physiological parameters of Cabernet Sauvignon and Chardonnay wines fermented by indigenous _S. cerevisiae_. Figure 5: Volatile profile in Cabernet Sauvignon wines fermented by 11 indigenous _S. cerevisiae_ strains with varying genotypes. (**A**): Heatmap analysis of volatile compounds in Cabernet Sauvignon wines. (**B**): Aroma attributes of the Cabernet Sauvignon wines. Principal component analysis (PCA) score (**C**) and loading (**D**) plots of the Cabernet Sauvignon wines. Figure 6: Volatiles profile in Chardonnay wine fermented by 6 indigenous _S. cerevisiae_ strains with varying genotypes. **(A)**: Heatmap analysis of volatile compounds in Chardonnay wines. **(B)**: Aroma attributes of the Chardonnay wines. Principal component analysis (PCA) score **(C)** and loading **(D)** plots of the Chardonnay wines. \begin{table}
\begin{tabular}{l l l l l l l l l l l l l} \hline
**Compounds** & **XX** & **XX1** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** & **NCN** \\ \hline \multicolumn{14}{l}{_Higher alcohols_} \\ \multicolumn{14}{l}{Phenyl Methyl 167,926.81 \(\pm\) 167,138.4 \(\pm\) 185,463.92 \(\pm\) 185,463.93 \(\pm\) 185,463.93 \(\pm\) 181,400.58 \(\pm\) 2,  
In Chardonnay wines, of the 50 volatiles identified and quantified, 47 showed significant difference (Table S6), among which concentrations of 13 compounds were beyond their sensory thresholds (Table 3). Again, the indigenous _S. cerevisiae_ population dedicated to more complex volatile compositions compared to the commercial reference strain TXL (Figure 6A). NX1 was inclined to yield a wide range of branched-chain alcohols whilst NX1, NX15, NX16 and NX18 generated higher amounts of pleophyticic esters (Figure 6A).