## 3 Materials and Methods
### Extraction and GC-MS Analysis of Volatile Compounds  
The extraction and analysis of grape volatile compounds were based on the reported method developed by our research group [21,38,39]. The grape berries with seeds removed were blended with 1 g polyvinylpolypyrrolidone (PVPP) and grounded under continuous liquid nitrogen. After maceration for 4 h at 4 \({}^{\circ}\)C, the mixture was centrifuged at 7104\(\times\)\(g\) (8000 rpm, 10 cm) at 4 \({}^{\circ}\)C for 15 min. Five milliliters of the clear juice with 10 \(\upmu\)L internal standard 4-methyl-2-pentanol (4M2P, 1.0018 g/L) and 1 g NaCl added were blended in a 15-mL sample vial tightly capped with a PTFE-silicon septum containing a magnetic stirrer. Afterwards the sample was equilibrated at 40 \({}^{\circ}\)C for 30 min while being stirred. Then the pretreated SPME fiber (50/30-\(\upmu\)m DVB/Carboxen/PDMS, Supelco, Bellefonte, PA, USA) was inserted into the headspace, extracting for 30 min with samples being continued heating at 40 \({}^{\circ}\)C and agitation. The fiber was immediately desorbed for 8 min in the GC injector. The analysis of C6 volatile compounds was performed on an Agilent 6890 GC equipped with Agilent 5975 MS fitted with a 60 m \(\times\) 0.25 mm HP-INNOWAX capillary column (0.25 \(\upmu\)m film thickness) (J & W Scientific, Folsom, CA, USA) as described in previous reports [21].  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**DAF** & **Muscat Tchervine** & **Gewürztraminer** & \multicolumn{2}{c}{**Syrah**} & \multicolumn{2}{c}{**Chardonnay**} \\ \hline
2010 & Brix & pH & Brix & pH & Brix & pH & Brix & pH \\
31 & 4.4 & 2.5 & 3.8 & 2.6 & 4.0 & 2.5 & 4.0 & 2.6 \\
43 & 5.7 & 2.5 & 4.8 & 2.7 & 4.8 & 2.5 & 3.9 & 2.7 \\
59 & 8.3 & 2.6 & 8.2 & 2.9 & 5.1 & 2.7 & 10.6 & 2.8 \\
73 & 19.5 & 3.0 & 15.9 & 3.0 & 13.8 & 2.9 & 18.5 & 3.2 \\
87 & 17.5 & 2.9 & 18.8 & 3.0 & 16.5 & 3.2 & 15.8 & 3.1 \\
101 & 20.4 & 3.0 & 22.5 & 3.2 & 19.3 & 3.3 & 20.9 & 3.4 \\
106 & 28.1 & 3.2 & 27.6 & 3.3 & 21.6 & 3.3 & 20.1 & 3.3 \\ \hline
2011 & Brix & pH & Brix & pH & Brix & pH & - & - \\
32 & 5.8 & 2.5 & 4.5 & 2.6 & 5.2 & 2.4 & - & - \\
48 & 6.7 & 2.5 & 6.9 & 2.6 & 5.6 & 2.5 & - & - \\
60 & 11.7 & 2.6 & 14.0 & 2.9 & 8.3 & 2.5 & - & - \\
75 & 18.7 & 3.0 & 17.5 & 3.2 & 16.9 & 2.9 & - & - \\
89 & 19.1 & 3.1 & 21.3 & 3.2 & 17.5 & 3.2 & - & - \\
102 & 24.2 & 3.2 & 18.4 & 3.1 & 21.4 & 3.3 & - & - \\
112 & 28.1 & 3.2 & 25.8 & 3.5 & 23.6 & 3.3 & - & - \\ \hline \end{tabular}
\end{table}
Table 2: Total soluble solids (\({}^{\circ}\)Brix) and pH of four grape berries (Syrah, Chardonnay, Gewürztraminer and Muscat Tchervine) at all developing stages.  
Retention indices of reference standards and mass spectra matching in the standard NIST 08 library were used in the identification of the volatile compounds. A synthetic matrix was prepared in distilled water containing 7 g/L tartaric acid and 200 g/L glucose, pH = 3.3. 4-Methyl-2-pentanol (10 uL) was added before detection as the internal standard. The chemical standards used in this work included hexanal, (_E_)-2-hexenal, hexanol, (_E_)-2-hexen-1-ol, (_Z_)-2-hexen-1-ol, (_E_)-3-hexen-1-ol, (_Z_)-3-hexen-1-ol and hexyl acetate. The standard solution was diluted into eight levels successively and volatile compounds of each level were extracted and analyzed using the same detection method as the grape samples. Standard curves of chemical standards and their lower and upper limit of detection (LOD) were listed in Table S4.