## 2 Results and Discussion
### Concentration of Total Volatile Compounds
In general, temperatures were higher (by 2-6 \({}^{\circ}\)C) and rainfall was higher according to data collected in SIAM (Sistema de Informacion Agraria de Murcia) [26] (data not shown), both of which might have contributed to the higher alcohol concentration. Several authors have reported the effect of climatological conditions on the accumulation of alcohol in wines, which, in our case, could have had effect on grape maturity; for instance, [PERSON] et al. [27] found that the content of C6 compounds decreased as fruit matured. In our study, the degree of maturity was greater in 2018 (Table 1), thus resulting in less alcohol content than in 2019 (Figure 1B). During alcoholic fermentation, a great number of esters may be generated as a result of the yeast metabolism, but the most abundant are ethyl esters of organic acids, acetates of fused alcohols, and ethyl esters of fatty acids [28]. It is generally believed that esters make the greatest contribution to the desirable fermentation bouquet of wine with its characteristic fruity odors [29]. The total concentrations of esters are shown in Figure 1C, where it can be seen that they were slightly higher in 2019 than in 2018. It is known that a higher Brix leads to a substantial decrease in the concentration of esters. According to [PERSON] et al. [30], after veraison there is less alcohol acyl transferase activity in the berries, and thus, higher ester concentrations in wines obtained from less mature grapes. This would agree with our results for the 2019 wines, a year in which we found a slightly higher quantity of these compounds, increasing the potential for synthesizing esters in grapes that were less mature than those harvested later in the ripening process (2018). In contrast, the MS30 wine showed lower concentrations of these compounds than Verdejo and the rest of the varieties. The results also showed that Verdejo and MC69 wines contained a greater quantity of esters in 2018 and MS33 the least. Verdejo and MC69 wines were again the two ones with the highest ester concentration in 2019, (Figure 1C). According to the results, therefore, the MC69 cross could be considered a good candidate for obtaining a wine with a quality similar to that of a Verdejo wine due to the higher concentrations of these compounds, which would translate into an aromatically fruity wine. One of the most important groups of volatile compounds in wines are those containing terpenes and norisoprenoids because both are related with quality attributes in wines. They are generally related with floral and citric notes of wine aroma, and are typical of aromatic grape varieties, their importance being related with their low odor threshold [24]. Tepene concentrations are often higher in grapes than in wines, perhaps because the bound terpene glycosides are hydrolyzed to produce volatile aroma compounds or converted into other compounds as a result of molecular rearrangements during fermentation [31]. This might be one of the main reasons for the relatively low quantities found in our study, and only the free terpen present in the wines were analyzed. The results obtained for this group of compounds are shown in Figure 1D for the two seasons studied. As can be seen, the MT103 wine differed significantly in this respect from the other wines, reaching the highest value in 2018, while the MV67 wine had the highest values in 2019, making this cross the most suitable for obtaining wines with more varietal aromas. In general, the concentrations were slightly higher in all the varieties in 2018 than in 2019, although less so in the case of MV67 and, especially, the MV7 cross, which provided higher concentrations of terpenes than the other crosses and Verdejo. It can be seen that Verdejo wine did not contain higher concentrations than the white crosses, which might mean that this wine would provide lower varietal aromas than some of our new white varieties.