## 3 Results and Discussion
### Gc-Ms
#### 3.1.3 Analysis of Xilovoltailes with a High Olfactory Impact  
Considering the quantitative analysis of the main wood-derived compounds present in the distillate, several statistically significant differences were highlighted among the samples. In this case, only samples treated with oak wood were considered. The most relevant results are shown in Tables 6 and 7. As previously reported, the heating of wood causes the thermodegradation of lignin and the formation of numerous aromatic compounds, including aromatic hydrocarbons, phenols and aromatic aldehydes [27]. Generally, low/medium levels of heating during cooperage lead to the formation of cinnamic and benzoic aldehydes, such as vanillin and syringaldehyde [16]. In our case, very high concentrations of vanillin, ethyl vanillate and syringaldehyde were obtained using the highest temperatures (Table 6). Is worth to note that the effect of toasting on the level of whisky lactone in spirits was weak, even if a greater concentration of this compound was noted in the untoasted theses. The use of different wood formats influenced the accumulation of xylvolatiles. With regards to the differences among wood assortments, the distillates refined with tablets were characterized by a higher concentration of benzoic aldehydes and, in particular, vanillin. Moreover, Table 7 shows how theses refined with sliced wood had a high content of both whisky lactone (boise, coconuts) and eugenol (spiced, cloves), two compounds with a primary role in defining the aromatic profile of distillates. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & **NT** & **Light** & **Heavy** & **Sig.** \\ \hline o-Guaiacol & 24 \(\pm\) 2 a & 25 \(\pm\) 1 a & 28 \(\pm\) 1 a & ns \\ Methylguaiacol & 2 \(\pm\) 0 b & 2 \(\pm\) 0 b & 33 \(\pm\) 16 a & *** \\ Vinylguaiacol & 24 \(\pm\) 2 b & 22 \(\pm\) 1 b & 34 \(\pm\) 2 a & *** \\ Eugenol & 102 \(\pm\) 89 a & 96 \(\pm\) 57 ab & 72 \(\pm\) 16 b & * \\ Vanillin & 660 \(\pm\) 118 b & 1140 \(\pm\) 276 b & 7534 \(\pm\) 1686 a & *** \\ Syringaldehyde & 839 \(\pm\) 169 b & 2640.0 \(\pm\) 947 b & 8624 \(\pm\) 2091 a & *** \\ Metoxyeugenol & 11 \(\pm\) 2 & 16 \(\pm\) 2 & 15 \(\pm\) 3 & ns \\ Phenol & 26 \(\pm\) 3 & 23 \(\pm\) 1 & 22 \(\pm\) 1 & ns \\ o-Cresol & 14 \(\pm\) 1 b & 14 \(\pm\) 0 b & 16 \(\pm\) 1 a & ** \\ p-Cresol & 6 \(\pm\) 1 & 5 \(\pm\) 1 & 5 \(\pm\) 1 & ns \\ _cis-whisky lactone_ & 97 \(\pm\) 63 a & 56 \(\pm\) 34 b & 64 \(\pm\) 41 ab & * \\ _trans-whisky lactone_ & 37 \(\pm\) 23 a & 22 \(\pm\) 13 b & 27 \(\pm\) 16 ab & * \\ Ethyl vanillate & 50 \(\pm\) 5 b & 68 \(\pm\) 11 b & 384 \(\pm\) 55 a & *** \\ Acetovanillone & 23 \(\pm\) 7 b & 30 \(\pm\) 7 b & 179 \(\pm\) 40 a & *** \\ Propiovanillone & 63 \(\pm\) 19 & 60 \(\pm\) 15 & 84 \(\pm\) 12 & ns \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The values represent the means measured for each toasting level \(\pm\) standard error (SE). All data are expressed in μg/L except where expressly indicated. Different letters within each row denote significant difference between the wines at \(p\) < 0.05 ([PERSON]’s post hoc test). *, ***, and ns: differences significant at \(p\) < 0.05, 0.01, 0.001 and not significant, respectively. The results refer only to the test samples treated with oak wood. Subsequently, a PCA considering only xylovolatile compounds was carried out with the aim of highlighting compositive differences among the samples depending on the treatments. The analysis was performed on the whole dataset. Cumulatively, the first two main components explain about 61.6% of the dataset variance. In Figure 2, it is possible to identify two main groups of samples. All the distillates aged with heavily toasted woods are grouped on the right, due to their high concentrations of vanillin and related benzoic aldehydes. On the other hand, distillates with a low toasting level or aged with untoasted woods are placed very close on the left side of the score plot.