# The Application of Wood Species in Enology: Chemical Wood Composition and Effect on Wine Quality
## 4 Influence of Wood Species on the Wine Sensory Profile  
Aged wines show a distinctive sensory feature that is acquired throughout the aging process. In the last years, winemakers from outside of Europe began to make wines with potential new sensory profiles, and therefore, the application of diverse wood species for wine aging constituted a potential increasingly valid and widespread option. Wood barrel-aged wine is complex and its sensory perception results from the interaction of many compounds. However, only a few of the compounds extracted from the wood to the wine during barrel aging have a significant impact on the wine sensory characteristics (Table 7). The main volatile compounds released from wood with wine sensory impact are phenolic aldehydes and phenyl ketones, furanic compounds (furfurlural, hydroxymethylfurlural, furfuryl alcohol, and 5-methylfurlural), volatile phenols (guaiacol, 4-methylguaiacol, ethylguaiacol, vinylguaiacol, and eugenol), and \(\beta\)-methyl-\(\gamma\)-octalactones [121; 122]. Phenolic aldehydes and ketones give the characteristic vanilla aroma of oak wood-aged wines, with vanillin being the main compound, characterized by low sensory thresholds (0.3 ppm) in wine [30; 123]. Siringaldehyde, sinapaldehyde, and coniferaldehyde do not have a great sensory impact, although their perception thresholds are clearly higher and, therefore, at their usual concentration. Furanic compounds are responsible for the characteristics and pleasant aromas of almonds and toasted almonds [122], with an olfactory detection threshold in red wines of 20 mg/L for furfural and 45 mg/L for 5-methyl furural [123]. Maltol and other oxygenated heterocycles provide the aromas of caramel and notes of toast that also characterize wood-aged wines. Guaiacol contributes with a smell of toast and sweet smoke aroma, with an olfactory detection threshold as low as 0.05 ppm [124]; methyl-4-guaiacol and ethyl-4-guaiacol have the smell of burnt wood, while phenol has an ink odor. Eugenol is also of great importance for wine sensory characteristics as it gives a spicy aroma of clove with a sensory threshold of 0.5 ppm [124]; however, all the others give smoked/toasted notes [125]. \(\beta\)-methyl-\(\gamma\)-octalactones (_cis_ and _trans_ forms) are responsible for the coconut flavor, two isomers, _cis_ (\(-\)) and _trans_ (\(+\)), have been described [63; 126]. It is necessary to point out that the _cis_ isomer presents a perception threshold between 4 and 5 times less than the _trans_ isomer making its contribution to coconut perception much more important [125], namely 460 ug/L for the _trans_-isomer and 92 ug/L for the _cis_-isomer [127]. Phenol has a medicinal smoky aroma but a slight sensory effect as its olfactory detection threshold is nearby 40,000 ug/L; \(o\)-cresol and \(p\)-cresol have a medicinal aroma, with an olfactory detection threshold of 300 and 60 ug/L, respectively [75; 124]. Ethyl-4-phenol has an unpleasant animal smell, described as leather and even a horse odor. The presence of the latter compound is considered, as long as it exceeds its threshold perception, as a serious wine defect [124]. Wood also releases some nonvolatile compounds such as phenolic acids, coumarins, and especially ellagitannins into the wine [92], which contribute to wine texture and taste sensations, such as body and astringency [128]. [PERSON] et al. [114] showed that each wood species added a diverse intensity of aromatic and gustative descriptors, emphasizing the main intensity of caramel/almond, vanilla, and toasty notes in red wines aged in oak wood barrels, of smoky, spicy, and fruity notes in red wines aged in false acacia wood barrels, and of balsamic descriptors in the red wines aged in ash wood barrels. Moreover, [PERSON] et al. [129] referred that throughout wine aging in a barrel, volatile compounds extracted from oak wood contribute with aromatic notes of smoke, vanilla, and spices.