# Yeast Diversity during Spontaneous Fermentations and
## 3 Results and Discussion
### Viiiification Using Indigenous S. cerevisiae Strains with Differentiated Genotypes
These esters, described as contributing full-bodied fruity aromas, were commonly provided by non-_Saccharomyces_ yeasts [46]. Our findings highlight the potential of indigenous _S. cerevisiae_ in enhancing aromatic ester production that would attribute to the desirable fruity and floral aromas, especially NX16 and NX18 (Figure 6A,B). In contrast, the commercial strain TXL might enhance the green characters of the Chardonnay wines (Figure 6B). Interestingly, the volatile profiles of NX1, and NX16 Chardonnay wines display inconsistency with the corresponding Cabernet Sauvignon wines (Figures 5A and 6A), which is likely due to the interactions of _S. cerevisiae_ strains and the grape variety. For example, many fermentation-derived higher alcohols are produced from the corresponding amino acid metabolism through the Ehrlich pathway [58]. Factors like preferential consumption of amino acids between _S. cerevisiae_ strains and the amino acid composition of grape juice/must would clearly affect the higher alcohol formation, and subsequently exert influences on the corresponding esters. To visualize the relationship between _S. cerevisiae_ genotypes with all volatile compounds of Cabernet Sauvignon and Chardonnay wines, principal component analysis was conducted. The first three/two principal components (PCs) allowed clear separation of Cabernet Sauvignon and Chardonnay wines fermented by _S. cerevisiae_ with different genotypes (Figures 5C,D and 6C,D). For Cabernet Sauvignon wines, the first three PCs accounted for 65.6% of the variation in volatile compounds. Separation of PC1 was driven by a number of ethyl esters (e.g., ethyl phenylacetate and ethyl isovalerate) and some higher alcohols (e.g., 1-octanol, 1-decanol and 1-pentanol) (Figure 5C), with NX24, NX23, NX13, NX16 and XR located on the negative axis of the plot, and the rest of the wines located on the positive axis of the plot (Figure 5C). Phenethyl acetate and 3-methyl-1-butanol acetate drove the separation of PC2 towards the right hand-side of the plot, co-localising with NX16 wines, whilst ethyl phenylacetate and ethyl 9-decenoate drove the separation of PC2 towards the left hand-side of the plot (Figure 5C,D). Several higher alcohols such as 4-methyl-1-pentanol, 3-methyl-1-pentanol, 1-hexanol, and ethyl isovalerate drove the separation of PC3 towards the bottom of the plot (Figure 5D), co-localising with NX13 wines (Figure 5C). For Chardonnay wines, the first two PCs accounted for 61.5% of the variation in volatile compounds (Figure 6C). A clear separation according to different indigenous _S. cerevisiae_ was seen on PC1, which explained 34.5% of the overall variation. Among the tested _S. cerevisiae_, NX1, NX15, NX16, NX18 and TXL wines were located at the positive axis of PC1, and were associated with several ethyl esters of fatty acids (e.g., ethyl caprate), acetate esters (e.g., geranyl acetate) and fatty acids (e.g., n-decanoic acid) (Figure 6C,D) whilst NX13 and NX21 wines were on the bottom left quadrant of the plot (Figure 6C,D). PC2, accounted for 27.0% of variation, further separating NX1, NX15, NX16 and NX18 wines from the wines fermented by the commercial strain TXL (Figure 6C). TXL wines were located towards the bottom of PC2, and were primarily affected by higher production of 1-butanol, 1-decanol, 2,3-butanediol, 2-methyl-propanoic acid, and isobutyl acetate (Figure 6D). \begin{table}
\begin{tabular}{l c c c c c c c} \hline
**Compounds** & **TXL** & **NX1** & **NX13** & **NX15** & **NX16** & **NX18** & **NX21** \\ \hline _Higher alcohols_ & & & & & & & & \\
1-Hexanol & 1971.76 \(\pm\) 147.92 f & 2842.83 \(\pm\) 146.66 ab & 2651.52 \(\pm\) 74.29 abc & 2309.15 \(\pm\) 72.57 e & 2638.71 \(\pm\) 8