# Identification of Rotundone as an Important Contributor to the Flavor of Oak-Aged Spirits
## 2 Results and Discussion
### Relative Potency of Rotundone in Bourbon Whiskey
When characterizing a volatile compound, it is common to calculate its odor-activity value (OAV), which is the ratio of concentration of an odorant to its odor detection threshold. OAVs calculated using published odor detection thresholds [4; 39; 40; 41; 42; 43; 44] are shown in Table 5. Generally, the odor of a compound with an OAV above 1 is considered to be detectable in the product. Of the compounds quantitated, 19 out of the 25 had OAVs above 1. All of the ethyl esters fell into this category, with the exception of ethyl vanillate. Of the oak-derived odorants, (\(E\))-isoeugenol, guaiacol, eugenol, (\(Z\))-whiskey lactone, vanillin, \(\gamma\)-nonalactone, syringol, and rotundone qualify as potential flavor contributors. OAVs for (\(E\))-whiskey lactone, 4-ethylphenol, syringol, \(p\)-cresol, and syringaldehyde were all below 1. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Concentration (\(\mu\)g/L, ppb)**} \\ \cline{2-5}
**Compound** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **Sig.1 ** \\  & **(4 Year)** & **[PERSON] (8 Year)** & **[PERSON] (12 Year)** & \\ \hline
3-methyl-1-butanol & 962,000 (\(\pm\)4.0\%) & 1,090,000 (\(\pm\)4.5\%) & 1,420,000 (\(\pm\)4.9\%) & 0.97 \\
2-methyl-1-butanol & 379,000 (\(\pm\)4.3\%) & 462,000 (\(\pm\)4.1\%) & 727,000 (\(\pm\)4.5\%) & 0.96 \\
2-methyl-1-propanol & 224,000 (\(\pm\)4.4\%) & 321,000 (\(\pm\)8.5\%) & 419,000 (\(\pm\)8.6\%) & 1.0 \\
2-phenethyl alcohol & 33,800 (\(\pm\)0.40\%) & 41,700 (\(\pm\)1.4\%) & 39,100 (\(\pm\)1.4\%) & * \\ syringaldehyde & 7530 (\(\pm\)3.5\%) & 10,400 (\(\pm\)0.54\%) & 14,400 (\(\pm\)3.0\%) & 1.0 \\ acetal & 5390 (\(\pm\)3.7\%) & 5360 (\(\pm\)5.6\%) & 5170 (\(\pm\)0.49\%) & * \\ ethyl octanoate & 4790 (\(\pm\)5.2\%) & 3260 (\(\pm\)1.8\%) & 5830 (\(\pm\)3.0\%) & * \\ (\(Z\))-whiskey lactone & 2850 (\(\pm\)2.1\%) & 4330 (\(\pm\)2.3\%) & 5470 (\(\pm\)1.8\%) & 1.0 \\
3-methylbutyl acetate & 1910 (\(\pm\)0.66\%) & 973 (\(\pm\)2.7\%) & 1980 (\(\pm\)1.9\%) & * \\ ethyl hexanoate & 1500 (\(\pm\)2.8\%) & 1420 (\(\pm\)1.5\%) & 3110 (\(\pm\)2.8\%) & * \\
4-ethyl phenol & 72.7 (\(\pm\)0.71\%) & 58.4 (\(\pm\)0.82\%) & 91.2 (\(\pm\)9.1\%) & * \\ vanillin & 619 (\(\pm\)2.3\%) & 950 (\(\pm\)2.9\%) & 1410 (\(\pm\)1.9\%) & 1.0 \\
2-phenethyl acetate & 614 (\(\pm\)1.3\%) & 123 (\(\pm\)1.7\%) & 211 (\(\pm\)0.74\%) & * \\ ethyl butyrate & 458 (\(\pm\)1.0\%) & 740 (\(\pm\)2.2\%) & 1260 (\(\pm\)2.6\%) & 0.99 \\ guaiacol & 39.1 (\(\pm\)7.6\%) & 56.7 (\(\pm\)4.8\%) & 63.5 (\(\pm\)4.3\%) & 0.97 \\ (\(E\))-whiskey lactone & 316 (\(\pm\)0.48\%) & 457 (\(\pm\)0.81\%) & 586 (\(\pm\)2.3\%) & 1.0 \\ (\(E\))-isoeugenol & 306 (\(\pm\)2.4\%) & 368 (\(\pm\)3.5\%) & 416 (\(\pm\)7.7\%) & 1.0 \\ eugenol & 207 (\(\pm\)3.9\%) & 197 (\(\pm\)2.0\%) & 131 (\(\pm\)5.3\%) & \(-\)0.920 \\ syringol & 205 (\(\pm\)14\%) & 265 (\(\pm\)20\%) & 219 (\(\pm\)4.8\%) & * \\ \(\gamma\)-nonalactone & 145 (\(\pm\)13\%) & 190 (\(\pm\)3.7\%) & 175 (\(\pm\)14\%) & * \\ ethyl vanillate & 127 (\(\pm\)14\%) & 299 (\(\pm\)3.9\%) & 572 (\(\pm\)17\%) & 0.99 \\ ethyl 3-methylbutanoate & 85.0 (\(\pm\)1.0\%) & 183 (\(\pm\)3.1\%) & 313 (\(\pm\)11\%) & 0.99 \\ \(p\)-cresol & 18.0 (\(\pm\)4.0\%) & 26.9 (\(\pm\)26\%) & 23.6 (\(\pm\)7.8\%) & * \\ (\(E\))-\(\beta\)-damascenone & 6.56 (\(\pm\)2.1\%) & 3.58 (\(\pm\)2.6\%) & 3.62 (\(\pm\)2.1\%) & * \\ rotundone & 0.342 (\(\pm\)0.54\%) & 0.403 (\(\pm\)1.4\%) & 0.453 (\(\pm\)1.9\%) & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Concentrations for selected odorants in bourbon whiskeys aged for 4, 8, and 12 years. This is the first study in which rotundone was identified and quantitated in spirits. Although rotundone was measured in the parts-per-trillion range, its extremely low threshold value yielded an OAV well above 1, which increased with the age of the bourbon. Thus, it can be concluded that rotundone was clearly detectable and impacted the flavor of bourbon whiskkeys.