## 1 Introduction
farnetto_ [PERSON], _Q. oocarpa_ [PERSON] and _Q. humboldtii_ Bonpl and others less known such as _Q. serrata_, _Q. mongolica_ or _Q. denta_[5; 12]. In addition, the cooperage industry has been forced to offer a wider range of products from non-oak woods, such as _Robinia pseudoacacia_ L. (false acacia), _Castanae sativa_ Mill. (chestnut), _Prunus avium_ L. and _Prunus cereus_ L. (cherry), _Fraxitus excislo_ L. and _Fraxitus american_ L. (European and American ash, respectively) [12; 19; 20; 21; 22; 23; 24]. In fact, many of these woods had been used for many years, but most of them had been neglected in terms of cooperage use. However, due to the continuous quest to differentiate some wines from others, they have been given another chance. Others have been around for centuries, such as chestnut, but advances in the knowledge of wood, processes and ageing have led to the production of higher quality contact wood for wine. As a result, many producers are opting for local woods and are using barrels made from woods other than _Quercus_[5]. The components that are released from the wood to the wine are called the \"extractable fraction\" and represent approximately 10% of the dry wood weight. These compounds are difficult to classify due to their varied nature. Ellagitannis are the most abundant, but there are also others with different chemical structures such as low molecular weight phenols and volatile compounds. Some of these compounds are the origin of many of the interesting organoleptic characteristics found in wines that have been in contact with wood and their presence has led winemakers to increasingly use wood throughout the winemaking process [4; 5; 11; 12]. Volatile compounds from oak transferred to wine are of great sensory importance because they contribute aromatic notes of \"vanilla\", \"sweet\", \"almond\", \"wood\", \"coconut\", \"spice\", \"smoked\" and \"toasted\" (Table 1), increasing its complexity [25; 26]. The volatile compounds generally found in traditional oaks are those also found in alternative oaks and other woods. Despite this, the genus and species of wood affects the aromatic profile and there are compounds such as volatile phenols, lactones, furanic compounds, aldehydes and others that can differentiate them and, above all, provide quantitative and qualitative differences [13; 24; 27; 28; 29]. A clear example is the long-known generalisation with traditional oaks, where the highest amount of _cis_-\(\beta\)-Methyl-\(\gamma\)-octalactone lactone (_cis_ lactone) is associated with _Q. alba_[4; 18; 30]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Derived from** & **Common Name** & **IUPAC Name** & **Molecule** & **Aroma Notes** & **Olfactory Threshold** \\ \hline Volatile phenols & Lignin and polyphenols & Quasiacol & 2-Mehoxyphenylenol & \(\begin{array}{c}\text{{\sf{do}}}\text{{\sf{}}}\text{{\sf{}}}\text{{\sf{}}} \\  
Numerous factors influence the concentrations of volatile compounds found in wood or in wine aged with it, one of the most important being the wood toasting, although there are others, such as silvicultural treatments to the trees and the type of wood drying [40; 41; 42; 43]. The toasting of wood increases the quantity and complexity of the compounds yielded by the wood to the wine, as it induces the formation of new volatile compounds by thermal degradation of the wood or increases the existing ones. Depending on the temperature and exposure time, toasting can be light, medium or heavy. The temperature, time and toasting cooperate method (fire or hot air convection) also affect wood aroma compounds [13; 27; 43; 44; 45; 46]. Volatile phenols, phenolic aldehydes and phenylketones come from the thermodegradation of lignin [41]. These compounds mainly give the wine smoky, woody, vanilla and spicy aromas (Table 1). Furanic compounds come from the thermal degradation of polysaccharides [44], providing aromas of toasted almond, nuts, caramel, burnt sugar, bread and sweets (Table 1).