## 2 Materials and Methods
### Profiling of Wine Composition  
Basic oenological parameters of the resultant wine samples, including residual sugar, tittatable acidity, volatile acidity and ethanol, were determined following the protocols reported in OIV-INT-00-2020 (OIV, 2020). The pH of the wines was measured using a pH meter (Sartorius PB-10, Gottingen, Germany). Malic, lactic, citric, tartaric and acetic acids were quantified by HPLC (Agilent 1100, Agilent Technologies, Santa Clara, CA, USA) with an HPX-87H Column (300 mm \(\times\) 7.8 mm, BioRad, Hercules, CA, USA) under the following condition: mobile phase, 2.5 mM H\({}_{2}\)SO\({}_{4}\); flow rate, 0.5 mL/min; column temperature, 60 \({}^{\circ}\)C; injection volume, 20 uL. Signals were detected using an Agilent G1315B diode array detector at 210 nm. The organic acids were quantified from external calibration curves of the corresponding standard solutions using Agilent ChemStation Software (Version B.01.03).  
Volatile compounds were extracted and analysed using headspace solid-phase microextraction-gas chromatography with mass spectrometry (HS-SPME-GC-MS) as described by [PERSON] et al. [28] with some modifications. Briefly, each wine sample (5.0 mL) was transferred to a 20 mL screw-cap glass vial containing 1.0 g NaCl and 10 uL internal standards (4-methyl-2-pentanol, 20 mg/L). The vials were incubated at 40 \({}^{\circ}\)C with 400 rpm agitation in a CTC CombiPAL auto sampler (CTC analytic, Zwingen, Swiss) for 30 min. Volatile extraction was performed subsequently using a 50/30 \(\upmu\)m DVB/CAR/PDMS SPME fibre (Supelco, Bellefonte, PA, USA) for 30 min with continuous heating and agitation at 250 rpm and 40 \({}^{\circ}\)C. The fibre was then desorbed at 250 \({}^{\circ}\)C in the GC injector for 8 min using splitless inlet injection mode. Volatiles were subjected to gas chromatography-mass spectrometry analysis using an Agilent 6890 GC system combined with an Agilent 5975 MS detector. The GC-MS unit was equipped with an HP-INNOWAX capillary column (60 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m, J&W Scientific, Santa Clara, CA, USA) for volatile separation. Volatile compounds were carried by ultra-pure helium with a flow rate at 1 mL/min. GC program started at 50 \({}^{\circ}\)C and held for 1 min, then ramped to 220 \({}^{\circ}\)C at a rate of 3 \({}^{\circ}\)C/min, and held at this temperature for 5 min. Temperature of both the transfer line and the ion source was set at 230 \({}^{\circ}\)C, while the quadrupole was maintained at 150 \({}^{\circ}\)C. Ion-electron impact spectra at 70 eV were collected in the range m/z 29-350 with scan mode at 0.2 s interval.  
Standard calibration curves were obtained using volatile compound standards in a chemically defined medium containing 14% \(v/v\) ethanol and 5 g/L tartaric acid, at pH 3.8. Mixture of standard volatiles was then blended with 10 uL internal standard (4-methyl-2-pentanol, 20 mg/L), and analysed following the same HS-SPME-GC-MS protocol as outlined above. Volatile compounds were identified using the retention time of the corresponding volatile standards and the NIST library, and were quantified using five-point standard calibration curves [28].  
Odour activity values (OAVs) of each identified volatile compound was used to indicate their contribution to wine aroma perception, and was calculated as follows [29]:  
\[\text{OAV}=\text{VC/OTD}\]  
where VC refers to the concentration of each individual volatile compound (\(\upmu\text{g}/\text{L}\)), and OTD is the odour threshold of the corresponding volatile reported in wine/wine-like medium [30; 31; 32; 33; 34; 35; 36; 37; 38; 39].