## 3 Results and Discussion
### SPME-GC/MS Results
At the end of fermentation, the mean peak area of citronellyJ acetate was similar for both yeast strains (SafAle US-05: 4.49 \(\times\) 10\({}^{6}\)\(\pm\) 5.53 \(\times\) 10\({}^{5}\) and SafAle WB-06: 4.39 \(\times\) 10\({}^{6}\)\(\pm\) 9.80 \(\times\) 10\({}^{5}\)). The production of citronellol by SafAle US-05 and SafAle WB-06 followed a similar pattern, with similar abundance at each time point. Studies using GC/MS generally only provided a snapshot of the volatile profile of beer at a single time point, often at the end of fermentation. As a result, this approach has previously missed important dynamic changes in volatile production that occurred over the course of fermentation. Taking dynamic measurements throughout the fermentation provides a more comprehensive understanding of yeast metabolism and strain-dependent differences. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number** & **Compound** & **Formula** & **CAS** \\ \hline
1 & Ethyl Acetate & C\({}_{4}\)H\({}_{3}\)O\({}_{2}\) & 141-78-6 \\
2 & Ethanol & C\({}_{2}\)H\({}_{6}\)O & 200-578-6 \\
3 & Ethyl protonate & C\({}_{3}\)H\({}_{3}\)O\({}_{2}\) & 105-37-3 \\
4 & Ethyl bunanoate & C\({}_{4}\)H\({}_{2}\)O\({}_{2}\) & 105-54-4 \\
5 & Isobutyl alcohol & C\({}_{4}\)H\({}_{10}\)O & 78-83-1 \\
6 & Isoamyl acetate & C\({}_{7}\)H\({}_{14}\)O\({}_{2}\) & 123-92-2 \\
7 & Isoamyl alcohol & C\({}_{8}\)H\({}_{20}\)O & 123-51-3 \\
8 & Ethyl hexanoate & C\({}_{8}\)H\({}_{6}\)O\({}_{2}\) & 123-66-0 \\
9 & Ethyl octanoate & C\({}_{0}\)H\({}_{20}\)O\({}_{2}\) & 106-32-1 \\
10 & Acetic acid & CH\({}_{3}\)COOH & 64-19-7 \\
11 & Ethyl decanoate & C\({}_{2}\)H\({}_{24}\)O\({}_{2}\) & 110-38-3 \\
12 & Isoamyl octanoate & C\({}_{23}\)H\({}_{20}\)O\({}_{2}\) & 2035-99-6 \\
13 & Citronelly acetate & C\({}_{23}\)H\({}_{20}\)O\({}_{2}\) & 150-84-5 \\
14 & Ethyl 9-decenoate & C\({}_{23}\)H\({}_{22}\)O\({}_{2}\) & 67233-91-4 \\
15 & Germany acetate & C\({}_{23}\)H\({}_{23}\)O\({}_{2}\) & 105-87-3 \\
16 & Citronello & C\({}_{10}\)H\({}_{20}\)O & 106-22-9 \\
17 & Ethyl dodecanoate & C\({}_{4}\)H\({}_{25}\)O\({}_{2}\) & 106-33-2 \\
18 & Geranil & C\({}_{6}\)H\({}_{18}\)O & 106-24-1 \\
19 & Phenylethyl alcohol & C\({}_{6}\)H\({}_{10}\)O & 60-12-8 \\
20 & Octanoic acid & C\({}_{8}\)H\({}_{16}\)O\({}_{2}\) & 124-07-2 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Compounds detected at the end of fermentation with SPME-GC/MS. Figure 2: Score plot of the first two principal component analyses (PCA) of VOC produced during fermentation (5 days) by commercially available yeast: _S. cerevisiae_ strain SafAle US-05 and _S. cerevisiae_ _var Diastaticus_ strain SafAle WB-06 (n = 2). Different colours represent the different days of fermentation. Figure 4: Time evolution of VOCs determined with SPME-GC/MS GC–MS. Quantification is given in the peak area detected under the curve, which can be quantitatively compared between the different measurements. Data presented as the mean peak area \(\pm\) standard deviation of two replicates. Figure 3: Correlation circle plots from the PCA applied to GC/MS data. Correlation circle plots display the correlation structure between compounds produced throughout fermentation in the space spanned by PC1 and PC2. The numbers represent the name of the compound displayed in Table 4.  
[PERSON] et al. (2013) [14] investigated terpene production between two yeast strains, _S. cerevisiae_ strain S288c and a haploid strain 59a derived from a wine strain EC1118. Each yeast was added to a synthetic must medium (MS300) with geraniol (1 mg/L). Stir bar sorptive extraction (SBSE) and GC-MS analysis showed a rapid disappearance of geraniol from the medium, followed by the appearance of citronellol, nerol and linalool, and finally, geranyl- and citronellyl acetate were synthesized by both yeast stains. Neither nerol nor linalool was observed in the current study. Commercial yeast strains have been developed to meet the specific requirements of brewers with regard to stress resistance, brewing performance, enzyme release and the profile of aromatic compounds produced.