# The Application of Wood Species in Enology: Chemical Wood Composition and Effect on Wine Quality
## 3 Impact of Wood Species on Wine Chemical Composition
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & \multicolumn{3}{c}{**Toasting Level**} & \\ \hline
**Volatile** & **Without** & **Light Toasting** & **Medium** & **Strong** & **Gray** & **Oak Species** & **References** \\
**Compounds** & **Toasting** & **Light Toasting** & **Toasting** & **Toasting** & **Oak Species** & **References** \\ \hline \multirow{5}{*}{_Trans-\(\beta\)-methyl-\(\gamma\)-octalactone} & nd-8.3 & nd & 4.8–7.0 & 5.0–7.2 & _Q. pyrenaica_ & \\  & 4.0–5.0 & nd & 6.4–7.4 & 4.2–7.4 & _Q. alba_ & [11](1) \\  & 5.0–6.7 & nd & 5.4–11.3 & 5.3–11.5 & _Q. petraea_ & \\ \cline{2-6}  & nd & 3.35 & 6.63 & 2.78 & _Q. alba_ & \\  & nd & 11.5 & 9.65 & 4.43 & _Q. petraea_ & [16](2) \\ \hline \multirow{5}{*}{_Cis-\(\beta\)-methyl-\(\gamma\)-octalactone} & 5.3–10.0 & nd & 3.6–13.7 & 2.9–9.6 & _Q. pyrenaica_ & \\  & 22.3–23.1 & nd & 26.5–45.5 & 16.1–23.6 & _Q. alba_ & [11](1) \\ \cline{1-1}  & 14.0–21.3 & nd & 14.1–18.5 & 7.4–18.2 & _Q. petraea_ & \\ \cline{1-1} \cline{2-6}  & nd & 24.9 & 31.1 & 14.6 & _Q. alba_ & \\ \cline{1-1}  & nd & 11.4 & 12.1 & 7.59 & _Q. petraea_ & [16](2) \\ \hline \hline \end{tabular} \({}^{(1)}\) mg/g dried wood; \({}^{(2)}\) mg/g wood; \({}^{(3)}\) mg/100g wood; nd—not detected.  
\end{table} 
Table 3: _Cont._authors described that in Merlot wine, with higher alcohol content, the removal of volatile compounds from wood barrels was higher than in Cabernet Sauvignon wine with lower alcohol content. These authors also observed that the alcohol degree has a higher effect on the removal process than the wine pH. [PERSON] et al. [11], using model wine solutions, studied the influence of temperature, pH, alcoholic level, and aging time on the removal of some ellagic tannins (castalagin, vescalagin, grandinin, roburin D and E) and ellagic acid from _Q. pyrenaica_ wood chips (_Quercus pyrenaica_). In the removal conditions studied, the temperature was the key factor influencing ellagic acid and ellagic tannins evolution. The results suggest that a decrease/degradation of these compounds is less perceptible at low temperatures (12 \({}^{\circ}\)C). Another factor to have in consideration is the number of barrel utilization, as the extraction decreases with the increased number of uses [103; 102; 83]. In the experiment performed by [PERSON] and [PERSON] [102], fifteen barrels (7 American, 6 French, and 2 Hungarian) were used with Chardonnay wines in three successive vintages. These authors showed that the extraction rates were lesser in the one-year-old barrels than in the new barrels and lower in two-year-old barrels than in one-year-old barrels and that the levels of the compounds associated with toasting reduced significantly in the second year. [PERSON] et al. [104] showed that the compounds removed from the wood, no significant differences were detected in furfuryl compounds and 4-methylguaicol, between new and 3 times used barrel (French or American oak); however, the number of lactones, which are essential compounds for the sensory wine characteristics, were significantly decreased in used barrels. Moreover, [PERSON] et al. [103] studied the effect of the barrels' utilization time on the red wine volatile composition and showed that wood compounds such as syringaldehyde, vanillin, and _trans_-\(\beta\)-methyl-\(\gamma\)-octalactone, which are essential for the red wine aroma, were smaller than their perception threshold in barrel with 5 to 6 utilization times. This author also detected differences between the wines aged in used French and American oak barrels, so the wines aged in American oak presented levels of _cis_-\(\beta\)-methyl-\(\gamma\)-octalactone greater than its perception threshold, which was not observed in the wines aged in French oak. On the other hand, the wine aged in used French oak barrels presented a superior quantity of syringaldehyde, vanillin, acetovanillone, and ethyl lactate. Table 4 summarizes some results obtained by several authors on the volatile composition of some wines aged in French and American oak barrels, with different utilization times.