## 4 Discussion  
The wide use of a limited number of _S. cerevisiae_ strains as starter cultures of fermentation could standardize the aroma and analytical profile of wine [1; 29]. To overcome this problem, the use of selected native _S. cerevisiae_ strains as starter cultures of fermentation could be a suitable strategy [21; 22]. Another strategy to enhance the wine aroma complexity is the use of non-_Saccharomyces_ yeasts in sequential fermentations. Indeed, several studies emphasize the use of non-_Saccharomyces_ yeasts in winemaking for their attitudes to produce aromatic compounds (such as esters, terpenes, thiols) and modify some structural compounds as polysaccharides, volatile acidity and ethanol content [30; 31; 32; 33; 34; 35; 36]. In this work, we evaluated the fermentation performance of a native strain of _S. cerevisiae_ (DiSVA 708) improved for the absence of H\({}_{2}\)S production and reduced production of SO\({}_{2}\)[21] to be used in the production of organic wines with a low SO\({}_{2}\) content. In pure fermentation, DiSVA 708 strain exhibited a behavior related to vintage, highlighting that the composition of grape juice can affect the fermentation performance of yeast strain. In particular, the increase in different aromatic compounds was detected among the vintages: in 2017 vintage ethyl octanoate, responsible for fruity \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Vintages** & **Trials** & **Smell (Score)** & **Taste (Score)** \\ \hline \multirow{2}{*}{**2016**} & OKAY & \(6.78\pm 0.11\)\({}^{\text{\,ab}}\) & \(6.34\pm 0.08\)\({}^{\text{\,b}}\) \\  & DiSVA 708 & \(7.35\pm 0.12\)\({}^{\text{\,a}}\) & \(7.55\pm 0.40\)\({}^{\text{\,a}}\) \\ \hline \multirow{3}{*}{**2017**} & OKAY & \(5.94\pm 0.03\)\({}^{\text{\,c}}\) & \(5.89\pm 0.76\)\({}^{\text{\,c}}\) \\  & DiSVA 708 & \(6.00\pm 0.10\)\({}^{\text{\,c}}\) & \(7.17\pm 0.16\)\({}^{\text{\,a}}\) \\ \cline{1-1}  & Td/708 & \(5.78\pm 1.73\)\({}^{\text{\,c}}\) & \(6.66\pm 0.77\)\({}^{\text{\,ab}}\) \\ \hline \multirow{3}{*}{**2018**} & OKAY & \(7.13\pm 0.52\)\({}^{\text{\,a}}\) & \(7.39\pm 1.6\)\({}^{\text{\,a}}\) \\  & DiSVA 708 & \(6.29\pm 1.78\)\({}^{\text{\,b}}\) & \(6.61\pm 1.22\)\({}^{\text{\,ab}}\) \\ \cline{1-1}  & Td/708 & \(7.05\pm 0.21\)\({}^{\text{\,a}}\) & \(6.82\pm 0.63\)\({}^{\text{\,ab}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Sensory analysis of the wines obtained by pure and sequential fermentations in three vintages. Pure culture was carried out by _S. cerevisiae_ OKAY and DiSVA 708. The abbreviations Td/708 indicate sequential fermentations carried out by _T. delbrueckii/S. cerevisiae_ DiSVA 708, respectively. Data are means \(\pm\) standard deviations. Values displaying different superscript letters (\({}^{\text{\,ab,c}}\)) within each column are significantly different according to Duncan tests (\(p<0.05\)). Figure 3: Principal Component Analysis based on the data regarding the main by-products of fermentation and volatile compounds of the wines obtained by pure and sequential fermentations for all vintages: 2016, 2017, 2018. The abbreviations Td/DiSVA 708 indicate the sequential fermentations carried out by _T. delbrueckii/S. cerevisiae_ DiSVA 708.  
flavors such as apple, pear and peach [37; 38; 39] and in 2018 vintage phenyl ethyl acetate, responsible for floral and honey aroma [38]. On the other hand, isoamyl acetate (banana flavors) was consistently highly produced by DiSVA 708 strain which can be considered a distinctive aroma of the strain. On the contrary, OKAY(r) showed a more homogenous wine aroma across all three vintages with ethyl butyrate and n-propanol as a distinctive aroma compound [40; 41]. In sequential fermentation, the results showed an influence on analytical profiles of the Verdicchio wines by _T. delbrueckii_ selected strain. In particular, the sequential fermentation carried out during the 2017 vintage showed a reduced content of volatile acidity than the wine obtained by the pure fermentation of the native _S. cerevisiae_ DiSVA 708.