## 3 Results and Discussion
### Dry-Hopped Cider Analysis  
Each Gravenstein apple cider was dry hopped with a different variety of pressed pellet hop: Citra, Galaxy, and Mosaic. HS-SPME-GC-MS analysis was conducted after samples were in contact with the various hops for five days and eight days. This timeline was chosen because it falls within the published industry standard of 4-12 days for dry-hopping beer. Figure 5 shows the experimental chromatograms labelled with selected VOCs that were consistently observed across all samples. As illustrated by these experimental data, after only 5 days, a wide array of new VOCs is already present in the cider headspace. Fromday 5 to day 8 (3-day period) of dry hopping, total ester concentrations in Citra and Galaxy doubled. Over the same time span, total ester concentrations increased by a factor of 18 for Mosaic hops. As expected, the Mosaic hops sample also had the highest overall concentration of esters of all samples studied after 8 days of dry hopping. Esterification of hop-derived monocarboxylic acids with ethanol is likely the synthetic route to many of these volatile esters during dry hopping [6]. Terpenes, however, were added to the cider headspace most efficiently by Citra hops. Total terpene concentration doubled in the Citra sample from day 5 to day 8, whereas a negligible increase was observed for both Galaxy and Mosaic hopped samples. Not only did Citra hops yield the highest concentration of terpen after 8 days, they also generated the largest variety of unique terpen at concentrations greater than the LOQ. More investigation into the timeline for dry hopping cider is needed; however, these preliminary results suggest that dry hopping time could be shorter than many current beer industry practices, and added VOCs are heavily dependent on hop type. Although no sensory work was conducted for this study, many relevant perception threshold analyses have been previously published for the VOCs observed in these experiments. We have summarized those VOCs and their previously published aromas here. Supplementary Table S2 includes every hop-derived VOC with published odor descriptors and perception thresholds. For a complete list of all detected species during the dry hopping process, please refer to Supplementary Table S1. Five VOCs were semi-quantified above published perception thresholds in these samples, as shown in bold in Supplementary Table S2: \(\beta\)-myrcene, linalool, methyl hepatomaate, 2-nonanone, and propanoic acid. \(\beta\)-Myrcene (citrus, spicy [23,31]) was the only terpene found in all 6 hopped samples, and was also present at the highest concentration of all the terpen. As its name suggests, Citra hops produced the highest concentration of this citrus terpene. \(\beta\)-Myrcene has also been identified as the predominant aroma compound in other hop varieties [8]. Linalool (citrus, floral [23,31]) was also semi-quantified above the perception threshold in both Citra- and Mosaic-hopped samples, but was not generated from Galaxy hops in detectable quantities. Previously established as one of the most important hop-derived odorants in dry hopped beer [6], linalool also contributes greatly to dry-hopped cider aroma. Overall, citrus aroma-contributors were much more concentrated in Citra- and Mosaic-hopped samples when compared with those hopped with Galaxy. Rather, Galaxy hops created more fruity VOCs, as evidenced by methyl hepatoma existing in quantifiable abundance only in this hop variety (fruity [32]). One floral ketone, 2-nonanone, was semi-quantified above the  
Figure 5: HS-SPME–GC–MS chromatograms are shown after 5 (**blue**) and 8 (**green**) days of dry hopping with three hop varieties (Citra, Galaxy, and Mosaic). Select VOCs that originated from the hops and were consistently detected across samples are numbered here.