## 2 Results and Discussion
### Concentration of Individual Aromas in the Different Families of Volatile Compounds
#### 2.3.5 Miscellaneous  
This group is based on two kinds of compound, one vinyl phenol (4-vinyl-guaiacol) and one sulfur derivate (3-methyl-thio-1-propanol). Vinyl phenols are typically not present in red wines due to the inhibitory action of some tannic substances on these enzymes, but they are the main phenols present in white wines [55]. Most volatile phenols have a negative effect on wine quality; for example, ethyl phenols are responsible for animal and smoky odors, whereas vinyl phenols are associated with strong pharmaceutical odors. However, the compound that we quantified was 4-vinyl-guaiacol, which has aromas of spices like clove or curry [35]. The other miscellaneous compound was 3-methyl-thio-1-propanol, which is related with the catabolic pathway and formed from the amino acid methionine, whose presence depends on the variety of grape [56] and which has descriptors such as cauliflower, cabbage, or potato [57] or aromas related to cooked green beans, wet brush, or greenodor [58]. The only \"thio\" found in this group in our wines was 3-methyl-thio-1-propanol, which, it has been suggested, is formed from the deamination of methionine (sulfur amino acid), followed by decarboxylation and reduction reactions during fermentation [59].  
In 2018, the highest concentration of 4-vinyl-guaycol (Table 3) was found in the MV11 wine, while MT103, MS33, and MC180 wines had the lowest values, and Verdejo wine did not show a high concentration of this compound. [PERSON] et al. [17] also quantified this compound in Vidal IHV (interspecific hybrid _Vitis_) wines, in which it was the main volatile phenol identified, and demonstrated that its odor threshold was 40 \(\mu\)g/L in wines, suggesting that it may affect wine aroma (OAV \(>\) 1). As regards 3-methyl-thio-1-propanol, the MC180, MS82, MT103, MV67, and MV7 wines had higher concentrations than Verdejo wine, suggesting cooked vegetable notes, but they were not perceived by the tasters in sensory analysis.  
In the 2019 season (Table 4), the concentration of 4-vinyl guaiacol was higher in Verdejo, MV11, MV67, and MV7 wines than in 2018, probably due to the moment of harvest. These results are contrary to those found by [PERSON] et al. [60], who reported higher levels of 4-vinyl guaiacol in late harvest Fiano wine. By comparison, MC180, MC69, MS30, MS33, MS82, and MT103 wines showed only slight changes in their concentrations. The presence or absence of this compound depends on several pathways; for example, according to [PERSON] et al. [61], 4-vinyl guaiacol in white wines is formed by yeasts through the decarboxylation of ferulic acid, while [PERSON] et al. [62], also in Fiano white wine, suggested it was formed as a result of glycosides hydrolysis, a pathway that would appear to merit further investigation. Finally, [PERSON] et al. [63] found that 4-vinyl guaiacol with its spicy, clove character, was generated through the breakdown of lignin.  
In 2019, the concentrations of sulfur compounds were lower than in 2018 for all the varieties studied, also would have been affected by the time of harvest, which would have improved the sensory quality of wines.