# Identification of Rotundone as an Important Contributor to the Flavor of Oak-Aged Spirits
## 2 Results and Discussion
### Quantitation of Rotundone  
The results from rotundone quantitation in bourbons, and other aged spirits, are shown in Table 2. Results indicate that rotundone is, indeed, transferred from the oak wood into the distilled spirit, potentially having a significant impact on its flavor. Among the oak-aged samples analyzed, Johnnie Walker Black Label Scotch Whiskey and Appleton Estates Extra Rum had the lowest concentration at 0.150 \(\upmu\)g/L and 0.152 \(\upmu\)g/L, respectively, which is not surprising as both employ used whiskey barrels in the aging process. Scotch maturation is done in casks that are used, repaired, re-charred, and then reused [22]. Rum has no legal requirements as to the cask used in aging, but it is required that casks be coded according to their origin or previous history, i.e., \"F1\" and \"F2\" for fresh first and second fill, respectively, and \"UR\" for an unclassified refill [23]. Based on the quantitation results in the other samples, it was revealed that age is apparently not the only factor contributing to rotundone concentration considering that 12-year-old bourbon (Jim Beam) had a lower concentration (0.342 \(\upmu\)g/L) than a 6-year-old (0.694 \(\upmu\)g/L) and a 10-year-old Bourbon (1.35 \(\upmu\)g/L) obtained from a different distillery (Bulleit). The rye from Bulleit contained one of the highest rotundone concentrations among the whiskey evaluated, suggesting that factors in their manufacturing process, other than age, may have had an effect. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**Odor Description**} & \multirow{2}{*}{**RI (Rtx-5) b**} & \multicolumn{2}{c}{**Detected by G–CO**} \\ \cline{3-5}  & & & **French** & **American** \\ \hline \multirow{4}{*}{
\begin{tabular}{c} hexenal \\ heptanal \\ unknown \\ 3-octanol \\ \end{tabular} } & _green, cut-grass_ & 811 & + & + \\  & _citrus, orange_ & 904 & + & + \\  & _earthy, mushroom_ & 912 & & + \\  & _mushroom_ & 982 & + & + \\  & _o-_cresol c & _croscoe, inky_ & 1062 & & + \\  & _p-_cresol c & _harryard, bandwidth_ & 1083 & & + \\  & guaiacol & _smokey_ & 1085 & + & + \\
4-hydroxy-2,5-dimethyl-3(2_H_)-furanone c & _caramel, burnt sugar_ & 1096 & + & + \\  & dihydromalol c & _caramel_ & 1101 & & + \\  & maltol c & _caramel_ & 1110 & & + \\
3-hydroxy-4,5-dimethyl-2(5_H_)-furanone c & _carry, maple_ & 1114 & & + \\  & (Z)-2-nonenal & _hay/slale_ & 1149 & + & + \\  & (_E,Z_)-2,6-nonenal & _melon, cucumber_ & 1156 & + & + \\  & (_E_)-2-nonenal & _hay/slale_ & 1161 & + & + \\  & (_E,E_)-2,4-nonenal & _fatty, fried_ & 1217 & & + \\  & (_E_)-oak lactone & _herbaceous, coconut_ & 1294 & + & + \\
4-ethylguaiacol & _smokey, cloves_ & 1274 & + & + \\  & thymol & _wood, thymme_ & 1293 & & + \\ \(p\)-vinylbquaiaicol & _smokey, cloves_ & 1321 & + & + \\  & (_Z_)-oak lactone & _herbaceous, coconut_ & 1331 & + & + \\  & Syringol & _smokey_ & 1356 & + & + \\ (_E_)-2-undecan c & _fresh, fatty, calintro_ & 1366 & & + \\  & eugenol & _spicy, cloves_ & 1362 & + & + \\ \(\gamma\)-nonalactone & _fatty, peach_ & 1368 & & + \\  & vanillin & _vanilla_ & 1392 & + & + \\ \(\gamma\)-decalactone & _fatty, peach_ & 1463 & & + \\ (_E_)-isoeugenol & _spicy, cloves_ & 1463 & + & + \\ (_Z_)-6-dodecen-\(\gamma\)-lactone & _creamy, dairy_ & 1665 & + & + \\ \(\delta\)-decalactone & _floral, peach, coconut_ & 1501 & & + \\ _unknown_ & _spicy, woody, incense_ & 1724 & + & + \\ \hline \hline \end{tabular}  
* Extracts prepared according to method 3.3.1. b GC retention index. c Tentatively identified compound.  
\end{table} 
Table 1: Odor-active compounds extracted a from toasted American and French oak woods. Climate humidity and temperature may influence volatile extraction during oaking of spirits. Generally, in lower-humidity climates, water evaporates from casks faster, resulting in spirits with higher ethanol content and a higher concentration of extracted volatiles [24]. Aging at higher temperatures was also reported to result in an increase in oak volatiles in the spirit [23].