## 3 Results and Discussion
### Cider VOC Profiles Resulting from Different Yeast Strains
This minty volatile had the lowest perception threshold of any other reported in this study (0.1 \(\mu\)g\(\cdot\)L\({}^{-1}\)), and it has been previously observed in cider and wine [4; 21], although it is not consistently listed as a top contributor to cider aroma [10]. Hexyl acetate (the second lowest perception threshold reported herein, 0.2 \(\mu\)g\(\cdot\)L\({}^{-1}\)), 3-methylbutyl acetate, ethyl-2-methylbutanoate, and diethyl butanedioate contribute greatly to fruity, strawberry, banana, and sweet caramel odors, and they were detected exclusively in cider produced with Abbey yeast. Rosy, floral volatiles (ethyl-9-decenoate and phenylethyl acetate) and citrus odorants (1-octanol) were identified in both French Saison and Abbey ciders but not in those produced with other yeast strains. These data indicate that French Saison is a good choice for producing a floral aromatic cider with minty undertones, and Abbey is best for a balanced mixture of fruity and floral notes. They also suggest that aromatic species whose perception thresholds are particularly low (<1 \(\mu\)g\(\cdot\)L\({}^{-1}\)) should be considered important to cider aroma, in addition to those typically reported on [10]. The Edinburgh yeast strain yielded an aroma profile consisting of the predominant ethyl esters and higher alcohols that were observed in all four ciders but with the addition of a volatile phenol (4-ethylphenol) among its major VOCs (Table 1). Some volatile phenols have been described as adding a smoked, spice, or clove scent [4; 31], and in fact the Abbey yeast strain is commercially advertised as contributing appealing phenolic characteristics to finished beer products. The phenol 4-Ethylphenol, however, has been described as a \"horsey defect\" in a previous study on wine odor [40]. Although this detection is notable, we do not anticipate that the relative peak area of 0.08 is of great enough abundance to dominate the odor characteristics of this cider. Edinburgh yeast resulted in several unique, fruity, and floral cider odorants that were not observed in the other ciders as well: 3-methylbutyl octanoate (fruity, floral), phenylethyl acetate (rose, honey), and 3-methylbutyl n-decanoate (fruity), as shown in Table 2. Lastly, the Belgian II yeast strain produced yet another original aroma profile with several VOCs of note. Ethyl esters of varying chain length contributed both a lily (ethyl tetradecanoate) and fatty (dodecanoic acid and ethyl hexadecanoate) odor to this final cider product. In addition to the 4-ethylphenol defect detected in Edinburgh cider, our analytical method proved efficient for sampling off-flavor esters (ethyl hexadecanoate), fatty acids (decanoic acid), and other phenols (4-ethyl-2-methoxyphenyl) across our cider samples as well. Previous studies have focused on sampling similar compounds for beer [9], but this work represents a novel method for off-flavor determination in cider. Although these VOCs may be produced as fermentation metabolites of the yeast strain under investigation, it is also well known that contamination of Brettanomyces/Dekkera strains that are resistant to SO\({}_{2}\) and filtration treatments could be partially responsible [13]. Whatever the source of these VOCs, it is of practical concern to cider makers to detect off-flavors early in the fermentation process, and this method makes that possible. Of the nine VOCs that are considered the top contributors to cider odor [10], we observed four as major species in all ciders produced in this study: ethyl acetate, ethyl octanoate, 2-phenylethyll alcohol, and 3-methyl-1-butanol. These four molecules are representative of the fruity, floral, and alcoholic aromas that are characteristic of cider. They also represent the two structural groups of molecules that were observed in the greatest abundance throughout this study: ethyl esters and higher alcohols.