# The Application of Wood Species in Enology: Chemical Wood Composition and Effect on Wine Quality
## 2 Chemical Composition of Wood Species  
A high quantity of studies has been published concerning oak wood chemical composition. The extractable wood compounds, ellagitannins, ellagic acid, gallic acid, several aldehydes, and aromatic compounds are the key compounds with interest for wine production and the aging process. According to several works [46; 47; 48; 49], volatile phenols and benzoic aldehydes play a very important role in the wines sensory profile. Other authors [48; 49; 50; 51] describe hydrolysable tannins as having particular importance as they give astringency, as well as being involved in the stabilization of wine compounds and demonstrating important antioxidant properties. According to [PERSON] [52; 53], ellagitannins have a significant role in the wine oxidation processes because they quickly absorb dissolved oxygen and facilitate the hydroperoxidation of wine compounds. In addition, they also demonstrate an essential role in the proanthocyanidin and anthocyanins condensation rate, avoiding their degradation and precipitation. For oak wood species studied with enological use, in general, the content of these extractives compounds is influenced by several factors, namely, the forest origin [11; 13; 54; 55; 56], species [54; 56; 11; 57; 58], heartwood age [59; 60], and most importantly, heat treatment which happens in coperage during barrel and wood fragment production [11; 12; 13; 58; 60; 61]. Several works [13; 53; 57; 58; 61; 62; 63; 61; 63] also describe that European and American species contain dissimilar levels of ellagitannin, with lower levels for American oak (_Q. alba_) compared to European species (_Q. robur_, _Q. petraea_, and _Q. pyrenaica_). Table 1 shows examples of several individual phenolic compounds detected in untoasted and toasted wood species (oak, cherry, and false acacia). Generally, the ranges for the most individual phenolic compounds, especially for ellagitannins in the same oak species, are broad due to factors such as the toasting process that occurs in cooperage and also variability within the species. According to several authors, false acacia and cherry do not contain ellagitannins in their composition [64; 65; 66; 67; 68]. [PERSON] et al. [69] detected in _Castanea sativa_ Mill (chestnut) a very low quantity of the two main ellagitannins, vescalagin and castalagin. The outcomes also show that its heartwood has the greatest comparable polyphenic profile to oak wood. Nevertheless, there were also some dissimilarities. Thus, in agreement to [PERSON] et al. [70], 1-O-galloyl castalagin, which was for the first time detected in chestnut wood samples, might originate from the esterification of castalagin or vescalagin with a gallic acid residue. For [PERSON] et al. [53], _Q. franetto_ is distinguished particularly from the other species by its greater concentration of pentosylated dimers and a monomer level that is similar to the rest of the _Quercus_ species, which makes it the species designated with the high concentration in ellagitannins. Ellagic acid could also be detected in diverse wood species, including oak, cherry, false acacia, and chestnut [68; 71]. According to several authors [65; 67; 72], cherry wood is characterized by a richness of procyanidins and (+)-catechin. This species also contains some phenolic acids and their esterification products (_p_-hydroxybenzoic acid, _p_-coumaric acid, benzoic acid, methylsyringate, 3,4,5-trimethylphenol, and methylvanillate), and flavonoids (naringenin, isosakuranetin, aromadendrin, and taxifolin). [PERSON] et al. [68] detected low values of naringenin for cherry woods. However, [PERSON] [73] also reported the existence of an extremely low content of procyanidins in oak woods. [PERSON] et al. [74] showed that the false acacia heartwood enclosed a greater quantity of flavonoids, namely, robinetin and dihydrorobinetin at values up to 100 \(\upmu\)mol/g. These compounds are specific markers of false acacia wood as they have not been found in other woods used for cooperage, such as oak, chestnut, cherry, and mulberry.