## 2 Results and Discussion
### Volatile Profiling  
A total of 64 volatile compounds (Table 7) were detected in the 27 wines using the described headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method. Of these 64 volatiles, only one compound (C31, methyl hexanoate) did not differ significantly among the wines (\(p<0.05\)) as determined by ANOVA. All significant correlations (\(p<0.05\)) between sensory descriptors and volatile compounds are summarized in Table 2. All significantly different compounds were used in the PCA to obtain the volatile space of the studied wines, shown in Figure 2. Again, the Kaiser criterion and the scree test were used to decide how many PCs to retain. The first two principal components (PCs) were kept, explaining 42% of the total variance. With the exception of W3 all wines of high quality (awarded either a gold or double gold medal) are positioned in the middle of the score plot (Figure 2a), indicating volatile profiles without any extreme concentration levels. Along the first PC, wines on the left hand side of the score plot (W16, W12, W14) show higher levels in even-numbered ethyl esters with 6 to 16 C-atoms (C35, C54, C61, C63, C64) and an unidentified terpene (C32) compared to wines positioned on the right hand side of the score plot (e.g., W3, W13, W21, W25, W26). These latter wines show higher concentration levels in 35 volatiles, including \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Region** & **Region Code** & **Fresh Green Aroma** & **Sweet Taste** \\ \hline North Coast & A & 1.0 c & 1.7 bc \\ Sonoma County & B & 1.3 bc & 1.3 c \\ Napa County & C & 1.0 c & 1.7 bc \\ Greater Bay area & D & 1.0 c & 1.7 bc \\ North Central Coast & E & 1.8 ab & 1.8 bc \\ South Central Coast & F & 1.3 bc & 2.0 bc \\ South Coast & G & 2.1 ab & 1.7 bc \\ Sierra Foothills & H & 1.5 b & 1.7 bc \\ Lodi/Woodbridge & I & 1.6 ab & 2.7 a \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean ratings of two sensory attributes, fresh green aroma and sweet taste, differ significantly among the nine wine regions in California, USA. Mean ratings in the same column sharing a common lowercase letter are not significantly different from each other (\(p<0.05\)). Mean values are calculated from two to four different wines per region and three sensory replicates for each wine. various linear and branched aliphatic alcohols (C3, C7, C12, C13, C16, C34), phenylethanol (C50), acetic (C5) and 3-methylbutanoic acid (C19), butyl and acetyl esters (C6, C15, C26, C45, C56, C57), odd-numbered and branched ethyl esters (C10, C14, C18, C22, C23, C27, C47, C53, C62), together with limonene (C39), barrel-derived compounds such as oak lactone, furfural, diffurfuryl ether (C20, C28-C30, C58-C59), aldehydes (C2, C43, C49), and mesifuran (2,5-dimethyl-4-methoxy-3(2H)-furanone C44). It seems that at least two underlying phenomena contribute to this separation:  
(i) some of these compounds are related to ageing and/or oxidation reactions [37, 38, 39], e.g., ethyl-3-methyl butanoate (C23), diethyl succinate (C53), acetic acid (C5), and phenylethanol (C50) were reported to increase with increasing wine age, while various acetates, such as isoamyl acetate (3-methylbutyl acetate C25) decrease over time. (ii) wines were also separated by the presence of barrel-derived compounds, such as furfural (C20), and oak lactone (C58, C59). Depending on the type and how much new oak barrels were used in the production of the wines, the concentration in these volatiles can vary significantly [40]. This is further substantiated by significant correlations to the oak aroma descriptor for (_Z_)- and (_E_)-oak lactone (C58, C59), and butylolactone (C30) (Table 2). Figure 2: PCA of the volatile compounds that differed significantly among the 27 wines (\(p<0.05\)). **(a)** Score plot showing the volatile space of the wines.