## 2 Results and Discussion
### Volatile Profiling
Wines are color-coded according to their assigned quality categories based on the wine judgment—red for wines low in quality, (_i.e._, that were awarded no medal), dark yellow for medium quality (_i.e._, either a bronze or silver medal), and green for high quality (_i.e._, a gold or double gold medal). Barplots of volatile compounds that contributed significantly (\(p<0.05\)) to the separation **(b)** along the first principal component (PC 1), and **(c)** along the second principal component (PC 2). Along the second dimension PC 2, explaining an additional 10% of the total variance, wines are separated by their varying levels in 18 volatiles--positively correlated are hexanoic and octanoic acid (C33, C51), linear aliphatic alcohols (C3, C24, C34), ethyl hexanoate (C41), furfural (C20), and SO\({}_{2}\) (C1), while various ethyl esters (C6, C17, C21-C23, C53, C64), _p_-cymene (C38) and 4-ethylphenol (C52) are negatively correlated to PC 2. Besides a separation due to different wine age, expressed by the various acids, alcohols and esters, another phenomenon is apparent--whether the wine was affected by _Brettanomyces bruxellensis_, a spoilage yeast that is able to produce potent aroma compounds such as 4-ethylphenol, leading to typical \"Brett\" character, also described as barnyard, horse sweat, and leather, depending on the concentration levels and ratios of the involved compounds [41,42]. The levels of 4-ethylphenol measured in the wines were high enough for the trained panel to quantify, leading to a significant correlation between Brett aroma and 4-ethylphenol concentrations (Table 2). Another significant correlation between the sensory descriptor \"Brett\" was found for ethyl hexanoate (Table 2). Although not a major contributor to the typical Brett characters, ethyl hexanoate was reported to be produced by various Brettanomyces strains in wine [43]. Correlating the volatile compounds to the sensory attributes led to several significant relationships (Table 2): The two branched esters ethyl-2 and ethyl-3 methyl butanoate correlated significantly to overall aroma. The volatiles acetic acid (C5), ethyl acetate (C6), the branched alcohols C7, C12, and C13, the esters C15, C10, and C23, as well as 2-phenylethyl alcohol (C50), 2-phenylethyl acetate (C57), and phenylacetaldehyde (C43) correlated all positively to alcohol aroma. For canned vegetable aroma, two of three ethyl esters--ethyl pentanoate (C27) and ethyl heptanoate (C47)--showed a negative correlation (Table 2), indicating the absence of these compounds in wines that show high levels of canned vegetal aroma. On the other hand, ethyl-2-hexenoate (C42) was positively correlated to that sensory attribute (Table 2). Similarly for fresh green aroma, which showed a positive correlation to ethyl-2-hexenoate (C42), and negative correlations to the ethyl esters ethyl-9-decenoate (C60) and ethyl heptanoate (C47), as well as to limonene (C39) (Table 2). In the past, masking effects have been shown for fruits and green-vegetal attributes and compounds that are associated with these descriptors, such as \(\beta\)-damascenone and 2-methoxy-3-(2-methylpropyl)pyrazine (MIBP) [44,45]. Dark fruit aroma showed significant positive correlations to the ethyl and acetyl esters C9, C11, C27, C47, and C53 (Table 2). For red fruit aroma ethyl decanoate (C61) contributed positively while for 4-ethyl phenol (C52) a negative correlation was found. All these correlations are in agreement to previous studies that found that various linear and branched ethyl esters contribute to red and black berry aroma [39,44,46], and that high levels of 4-ethylphenol have a masking effect on fruit aroma perception [47]. For sweet aroma, described by the panel as _honey_, _caramel_, and _chocolate_, acetaldehyde (C5), various ethyl and acetyl esters (C6, C10, C27), as well as butylolactone (C30) and acetoin (C9) all correlated positively, while a negative correlation between ethyl hexanoate (C41) and sweet aroma was found (Table 2).