# Identification of Rotundone as an Important Contributor to the Flavor of Oak-Aged Spirits
## 2 Results and Discussion
### Quantitation of Rotundone
In addition to environmental conditions, it is important to consider that three different varieties of American white oak may be used for cooperage, which will likely influence the concentration of rotundone in a particular sprit. This is supported by a study which showed that the geographical origin of the trees used for barrels, seasoning of the wood, and the coopering method all have an effect on the volatiles in wine [25]. Additionally, barrel size was shown to affect extraction rates, where the lower volume to wood surface area resulted in more concentrated volatiles from oak in wine [26; 27]. Conclusive statements concerning the concentration of rotundone and aging time can be drawn from the data obtained in the current study, as demonstrated both in the Jim Beam and Bulleti bourbons. The Bulleti bourbons almost doubled the rotundone during aging from 0.694 \(\upmu\)g/L (6 year) to 1.35 \(\upmu\)g/L (10 year). The Jim Beam bourbons also showed an increase, although not as great, from 0.342 \(\upmu\)g/L (4 year) to 0.403 \(\upmu\)g/L (8 year) to 0.453 (12 year) (Table 2). One of the more interesting observations was that rotundone was present not only in aged tequila but also in unaged silver tequila. This was further confirmed by direct injection GC-O analysis of the unaged tequila, in which an odorant was detected with the same retention index and odor property as rotundone (data not shown). Quite possibly, rotundone also originates from the agave used in tequila manufacturing. Agave leaves are known to contain a wide variety of monoterpenes and sequiterpenes. A study profiling the terpene content from a variety of agave leaves using GC-MS reported 32 terpen in Agave tequilana [28]. This group demonstrated that terpen were also in the final distilled spirit, tequila, by identifying 29 different monoterpenes and sequiterpene using GC-MS [29]. In the past few years, rotudone has gone from an obscure sesquiterpene ketone to being identified in an array of herbs, spices, fruits, chicory and now in oak wood. We can speculate that it probably exists in many more natural materials. The more well-known it becomes, the more likely it is to be viewed as a more common odorant. With the extremely low odor detection threshold of 8 ng/L, rotundone is also likely to be potent in anything in which it is found. \begin{table}
\begin{tabular}{c c c} \hline
**Product** & **Concentration (\(\upmu\)g/L, ppb) a ** & **\% RSD b ** \\ \hline Jim Beam Bourbon (4 year) (JB 4) & 0.342  & 0.54  \\ Jim Beam Black Bourbon (8 year) (JB 8) & 0.403  & 1.4  \\ Jim Beam Signature Craft (12 year) (JB 12) & 0.453  & 1.9  \\ Bulleti Bourbon (\(\sim\)6 year) & 0.694 & 0.12 \\ Bulleti Bourbon 10 (10 year) & 1.35 & 0.85 \\ W.L Weller Bourbon (12 year) & 0.393 & 1.8 \\ Eljiah Craig Bourbon (12 year) & 0.694 & 10 \\ Bulleti Rye Whiskey (-4 year) & 0.434 & 0.58 \\ Jack Daniels Tennessee Whiskey & 0.166 & 0.10 \\ Johnnie Walker Black Label Scotch & 0.150 & 2.2 \\ Whiskey (-12 year) & 0.152 & 1.8 \\ Appleton Estates Extra Rum (12 year) & 0.307 & 0.85 \\ Dilao Ariejo Tequila (18 month) & 0.100 & 1.1 \\ Milagro Silver Tequila & 0.100 & 1.1 \\ \hline \end{tabular}
\end{table} 
Table 2: Concentration of rotundone in oak-aged distilled spirits.