# Towards Sulphite-Free Winemaking: A New Horizon of Vinification and Maturation
## 3 Results and Discussion
### Aroma Composition  
Volatile compounds represent an important characteristic of wine products as they are responsible for the aroma, which is likely one of the most valuable quality feature able to influence consumer acceptability [53]. Wine aroma is conferred by the released volatile organic compounds (VOCs), the contents of which are influenced by the vineyard, fermentation, and ageing processes the wine undergoes [54], being responsible for primary, secondary, and tertiary aromas [53], respectively [55; 5]. The complete chemical composition of the must and the wines refined in both steel and wood barrels obtained with traditional and alternative viniification methods are reported in Table 5. Overall, 34 compounds were identified, covering 99.4-100.0% of the whole volatile profiles. Undoubtedly, the class of non-terpene derivatives was the most representative. Within this class, esters, accounting for 55.9-82.1%, were detected as the most abundant compounds in all the analysed samples, even though significant differences in their contents were found. Indeed, as evidenced by the one-way ANOVA, their content was significantly higher in the must obtained by the both traditional and Bioma viniification processes. This result corroborate the literature, since ethyl esters of fatty acids, after being produced in amounts exceeding their equilibrium concentration [53] during the fermentation stage, undergo a reduction on behalf of long-chain alcohols and volatile fatty acids, which, instead, face an increase in their concentration [5]. Volatile esters are among the most relevant classes responsible for the fruity aromas of wine products, and they derive mainly from the metabolism of fatty acids through enzymatic pathways [5]. They are defined as compounds formed by the condensation of a hydroxyl group of a phenol or an alcohol and a carboxyl group from an organic acid, and they are produced by yeasts during alcoholic fermentation, as well as during the malolactic fermentation. These molecules, if present in proper concentrations, confer pleasant notes, contributing to fruity and floral attributes and improving the quality of wines with poor varietal aroma characters [55]. Among esters, ethyl octanoate (16.9-40.7%), which is responsible for pineapple and strawberry hints, was the most abundant both in musts and wines, and together with ethyl hexanoate and ethyl decanoate, undergoes a reduction during viniification. Conversely, ethyl acetate increases when passing from must to wine, reaching almost 10-12% of the wine profile. Acetate esters are known to provide pleasant fruity aroma attributes. However, high concentrations of some of them, such as ethyl acetate, can negatively influence the wine, imparting a varnish and/or nail polish aroma, and also affecting the perception of favourable fruity ethyl esters by showing a suppressive effect. As previously reported, besides the reduction in esters during the viniification, an increase in long-chain alcohols and acids was also observed in the analysed samples. Higher alcohols represent the most important aroma contributors to wine as they are able to impart pleasant aromatic notes. Among the alcohols detected in the analysed wines, isoamyl alcohol, characterized by a marzipan scent [55]; phenylethyl alcohol, responsible for the rose aroma [55]; and amyl alcohol were the most representative compounds. Concerning acids, acetic acid was the only compound detected that belongs to this class, and although its content showed an increase passing from must to wine, it never exceeded 1.7%. This molecule, besides ethanol and glycerol, directly originates from glycolysis, which occurs during fermentation and is not responsible for the aroma bouquet of the beverage. However, it could affect the perception of flavours imparted by the volatile compounds [5]. These variations occur as a result of the ageing process, as well as due to the formation of the lees, which are also responsible for the removal of some unpleasant volatile phenols from the wine [55; 5].