## 3 Discussion
### The Content of Volatile Compounds That Contribute to the Aroma of Apple Wines
Experiments on rose wine aged with oak and cherry wood chips demonstrated minimal variation in the content of nearly all esters, with the exception of methyl vanillate, which exhibited higher concentrations in wines with oak wood. However, wines aged with cherry chips exhibited higher concentrations of the majority of the tested alcohols [19]. The results of this study yielded disparate findings. While wines aged with cherry chips exhibited elevatedconcentrations of numerous esters, those aged with oak chips demonstrated reduced levels of alcohol that contribute to aroma. To date, maple wood has not been employed for the maturation of wines. However, the findings of this study indicate that maple wood does not exert a distinctive influence on the volatile compound profile of apple wines. Only ethyl propanoate demonstrated a discernible impact on the olfactory characteristics of wines, particularly in wines aged with medium- and heavily toasted chips (Table 5). The results of the comparison between the ageing of apple wine in oak barrels and with oak chips are of interest. The alcohol content of the barrel-aged wine was lower than that of the wines aged with chips (Table 1), which corresponded with the higher total acidity (Table 1) and higher extract content (Table 1). Moreover, the concentration of most volatile compounds that contribute to the aroma of barrel-aged apple wines was relatively low, despite the much longer duration of this process compared to ageing with wood chips (Table 4). The largest statistically significant changes were observed for undecanol, hexyl acetate and methyl acetate, with the content of these compounds in the apple wine aged in the barrel being, respectively, over 10 times, approximately 4 times and 3 times lower than in the wine aged in the presence of oak chips, regardless of the degree of roasting. In contrast, the concentration of 2-methyl-ethyl butanoate ester was on average six times higher after barrel ageing than in the presence of wood chips. It was somewhat unexpected that wines aged in oak barrels for one year did not exhibit any more pronounced differences compared to wines aged with wood chips. The content of the other volatile compounds tested did not differ significantly between wines aged in barrels and those aged with wood chips (Table 4). Furthermore, there was no significant impact of the tested compounds on the results of olfactometric tests. The only notable difference was that wines aged in barrels exhibited a darker colour and a higher proportion of polyphenic compounds (Table 2), which are responsible for the antioxidant activity of wines (Table 2). Interesting results were obtained during sensory analysis (QDA) (Figure 1). Of the wines analysed, the wine aged with maple wood chips (heavily toasted) and cherry wood chips (medium-toasted) was given the highest overall note. Furthermore, this wine was characterised by a fruity and floral aroma, which was also confirmed by the olfactometric analysis (Table 5). Interestingly, however, there were quite low concentrations of undecanol and methyl octanoate in these highly sensory-rated wines, even though these compounds are perceived as \"fruity\". Also, lower concentrations of linanool oxide were more desirable in the sensory well-rated wines. It can also be noted that wines containing high amounts of propyl butanoate, diethyl butanoate and 2-phenylacetaldehyde were highly rated by the sensory panel. In contrast, the presence of furfural (roasted) and \(\alpha\)-pinene (herbaceous) in higher concentrations negatively affected the sensory evaluation results, which may be related to their dominant aroma and to a reduction in the perceptibility of fruit flavours. In turn, the wine aged in a barrel was characterised by a chemical and roasted aroma. It can therefore be concluded that the use of chips from various trees as an alternative to barrel ageing is a promising avenue for further investigation. This option is considerably less expensive than ageing in oak barrels [3; 17].