## 3 Results and Discussion
### Volatile Composition
#### 3.3.1 Free Volatile Compounds
However, the high standard deviation shown implies a high interannual variability. C\({}_{6}\) and C\({}_{9}\) aldehydes were originated from the oxidation process of fatty acids contained in grapes, as linoleic and linolenic acid, which could be responsible for herbaceous aromas [58]. In the free fraction, benzaldehyde, 2,5-dimethyl-, benzaldehyde and (\(E\))-2-nonenal were the major aldehydes identified (Tables 6 and 7), some of which have been reported to be compounds of significance in Noble muscadine wine. Benzaldehyde, 2-phenylethanol and methyl salicate are primarily derived from phenylalanine [29]. Aetaldehyde, phenyl-, stood out as the major aldehyde in 'Caino Tinto', being associated with hawthorn, honey and sweet descriptors [59]. Esters and phenols were detected in low concentrations in the grapes studied. Only two varieties, 'Caino Blanco' and 'Loureira', showed higher concentrations of esters, while 'Castanal' and 'Brancellao' showed higher concentrations of phenols. Nevertheless, standard deviations could be seen, possibly because of the interannual differences. Esters are related to the fruity character of wines [38] and those with black and red berry fruity notes are usually very important to red wine global aroma [27]. It is known that one of the differential factors in wine ester quantities will be the must composition of the grape variety [27]. Indeed, [PERSON] et al. [60] also referred to specific grape cultivar esters. [PERSON] et al. [58] considered that the wine ester diversity is a consequence of the genotypic varietal diversity of grapes used, explained by the availability of lipids in each variety. Regarding phenols, estragole was identified in all grape varieties with concentrations that ranged from 2 ug\(\cdot\)L\({}^{-1}\) in 'Loureira' and 'Souson' up to 27 ug\(\cdot\)L\({}^{-1}\) in 'Verdello Blanco'. This compound is associated with anise-like and herbaceous descriptors [61; 62]. [PERSON] and [PERSON] [62] referenced the presence of estragole, together with (\(E\))-anethole and methyl salicate in the must of the 'Madeleine Angevine 7672' grape variety. 2,6 ditert-butyl-p cresol (BHT) was the other phenol identified in almost all studied varieties but only in 2017. This compound was also previously identified in sherry wines [63]. \(P\)-cresol is a volatile compound present in smoke and it was also identified in some wines virified with grapes exposed to smoke that could even give them an ashy taste [64]. Considering the fact the area where the experimental vineyard is located suffered an important wave of fires in the 2017 vintage, it could be viable t think that the smoke has impregnated the grapes remaining up to their harvest. In the white grape varieties (Table 6), 2,4-di-tert-butyl- and phenol,4-ethyl- were the major phenols, 2,6-bis(1,1-dimethylethyl)-4-methyl- being the major phenol in the red ones, except for 'Caino Bravo' and 'Caino Longo 1' where estragole was the most abundant (Table 7). All varieties showed similar concentrations for ketones and PAH's, except 'Brancellao Blanco', which stood out for the lowest ketone values and 'Castanal' for the highest PAH content. Carbonyl compounds, such as ketones, are associated with rancidity and herbaceous odors and their origin is associated with lipoxygenase activity of the grape and must aeration [65]. Sulcatone has been identified in all studied varieties, its contribution mainly being important in the white grapes (Table 6). This compound was also identified by [PERSON] et al. [66] in Gewurztraminer wines and described as fruity, apple-like or creamy. With respect to the red grapes, acetophenone was the major ketone identified (Table 7). Lactones were detected in free form in all varieties. This group of volatile compounds is characterized by a fruity aroma, despite the fact that their sensorial characteristics are influenced by their chemical structure [67]. Among them, butylolactone, one of the better-known lactones was detected in 'Brancellao', 'Loureira' and 'Caino Longo 2'.