# The Application of Wood Species in Enology: Chemical Wood Composition and Effect on Wine Quality
## 1 Introduction  
Over the centuries, numerous wood species were used to manufacture wood barrels with mahogany, chestnut, pine, and false acacia wood as the most used species [1]. Nevertheless, oak has been one of the key wood species for this purpose, as it has diverse characteristics, which differentiate it from the other wood species, such as flexibility, ease to handle, resistance, and it has low permeability [2]. However, it is essential to remind that in the mid-twentieth century, there was a strong rejection of wood for enological purposes due to the incremented application of materials like concrete and stainless steel. From the 1990s onwards, the application of wood for cooperages, mainly from diverse oak wood species, reemerged rather significantly and became one of the main choices, for example, in aging wine [3, 4].  
The most oak wood species employed by cooperages are _Quercus alba_, _Q. garyrama_, _Q. macrocarra_, and _Q. stellate_ in the U.S.A., while other different oak species, specifically _Quercus petraea_ and _Q. robur_, but also other oak species, such as _Quercus cerris_, _Q. suber_, _Q. lyrata_, _Q. bicolor_ and _Q. lamyinose_ are used in Europe [5, 6]. However, are _Quercus alba_, _Q. petraea_, and _Q. robur_, the key oak species employed in the wine sector. Currently, several studies also described the application of other European and non-European oak species with remarkable use in winemaking, such as _Quercus figinaa_[7, 8], _Q. pubescens_[9, 10], _Q. pypenica_[11, 12, 13, 14, 15, 16, 17, 18, 19, 20], and also _Q. humbolditi_ from Colombia [21, 22].  
Actually, chestnut and oak wood species are permitted only by the Resolution OENO 4/2005 of Organization of Vine and Wine for enological use [23]. Nevertheless, in recent years, heartwood from other species has been considered for winemaking, especially for the aging process, such as false acacia, cherry, European and American ash, and mulberry.  
Additionally, scarce studies described the possible application of other wood species in enology like _Iuglans regia_[24].  
The main purpose of the wood barrels in enology is to enhance the wine with compounds extracted from the wood (such as phenolic compounds), stimulate reactions between wine and wood compounds, allow the air diffusion through the wood barrels' pores, and improve chemical reactions that happen gradually in wines and therefore increase wine's quality [25; 26]. Thus, in the last decades, the scientific literature contains a considerable quantity of study associated with the employment of oak wood barrels in enology, mainly its effect on wine chemical and sensory characteristics. The majority of research has focused on red wine, the use of oak barrels [15; 16; 20; 27; 28; 29; 30; 31], or the application of oak fragments, like chips, staves, blocks, or powders [10; 14; 28; 31; 32; 33; 34; 35]. Moreover, for rose wines, a few recent works report results about using diverse wood species, comprising oak, false acacia, and cherry [36; 37]. Finally, for white wines, there are also several works published concerning the application of diverse wood species, especially from oak and false acacia [38; 39; 40; 41; 42; 43; 44; 45].  
A comparative analysis between oak and non- oak wood species on wine chemical composition and sensory characteristics was the key objective of this review work. The chemical composition of diverse wood species with potential application in enology and the main factors determining their composition were also addressed. The review will be particularly useful for wine producers and winemakers, and all those who study this subject, as it shows a large amount of data on the use of different woods in enology, summarizing much of the information that has been published in the last twenty years.