## 3 Materials and Methods
### Experimental Design
#### 3.1.6 Sample Preparation  
The technique used in this study to quantify the precise concentration of aroma in a wine was headspace solid-phase microextraction (SPME), which has previously been applied to the analysis of volatile compounds in many wines because of its ease of use, good reproducibility, and lack of a need for large samples or solvents of any kind [67]. The fiber coating is the key to SPME, because different fibers have different selection and extractive efficiencies for volatile compounds [68]. In this study we used the PDMS/DVB/CAR fiber coating, as several authors have obtained good results with it; for example [PERSON] et al. [69] used it to study the effect of two elicitors, benzothiadiaole and methyl jasmonate, on the volatile compound composition of Monastrell grapes and wines, while [PERSON] et al. [50] used it to study the effect of using purified grape pomace as fining agent on the volatile composition of Monastrell wines. [PERSON] et al. [68] used it in the characterization of the key aroma compounds in Proso Millet wine and, finally, [PERSON] et al. [70] studied the volatile composition of Merlot red wine and its contribution to the aroma using, among others, this fiber. The chromatograms obtained can be seen in Figure S2, where the overlap of the Verdejo aromatic profile is seen together with a Monastrell, MC69 cross.  
Ten milliliters of wine were added to 20 mL vials with a magnetic screw top and polytetrafluoroethylene (PTFE)-lined septum, and then 25 \(\upmu\)L of 2-octanol as internal standard (100 ppm) (Sigma-Aldrich, Madrid, Spain) and 3 g of NaCl were added. A Gerstel auto-sampling device (Gerstel GmbH&Co. KG, Mellinghofen, Germany) was used. Gas chromatographic studies were carried out on an HP 7890B gas chromatograph (GC) system coupled to an HP 5977A quadrupole mass spectrometer (Agilent Technologies, Palo Alto, CA, USA), following the method described by [PERSON] et al. [69] and [PERSON] et al. [64]. The injector was run in splitless mode for 0.75 min with a 2 mm inner diameter non-deactivated direct liner for the SPME (Agilent Technologies) and a desorption time of 5 min. A divinylbezene (DVB)-carboxen (CAR)-polydimethylsiloxane (PDMS) fiber (Supelco, Bellefonte, PA, USA) and a DB-WAXetr capillary column (30 m \(\times\) 250 \(\upmu\)m, 0.25 \(\upmu\)m film thickness; Agilent Technologies) were used, with helium 8.0 as gas (Abello Linde SA, Barcelona Spain) and a column head pressure of 8 psi. The oven temperature was maintained at 40 \({}^{\circ}\)C for 0.5 min, raised to 260 \({}^{\circ}\)C at 4 \({}^{\circ}\)C min\({}^{-1}\) and then held at that temperature for 5 min. The mass spectrometer was operated in electron ionization mode at 70 eV with the detector in scan mode (mass range 20-350 amu) and the transfer line to the mass spectrometer system was maintained at 230 \({}^{\circ}\)C. Peaks were identified with the mass library (Wiley Registry 6.0; Wiley, Chichester, UK). The positively identified compounds were quantitatively analyzed by total ion current using the calibration curves proposed for each sample. All samples were analyzed in triplicate.