# Part II--Aroma Profile of Twenty White Grapevine Varieties: A Chemotaxonomic Marker Approach
## 1 Introduction  
The northwest of the Iberian Peninsula, including Galicia in Spain and the northern territories of Portugal, are specialized in the production of white wines [1; 2; 3; 4], recognized by their high quality and standing out for their freshness and good alcohol-acidity equilibrium, as well as for their aromaticity and fruity flavor [4]. Most of these wines are produced with autochthonous _Vitis vinifera_ L. varieties, considering 'Albarino', 'Treixadura' and 'Godello', which represent the most important varieties for the Galician economy [2]. Moreover, some Portuguese regions are well known for their white wines from varieties, such as 'Alvarinho' (syn. 'Albarino'), 'Loureiro' (syn. 'Loureira'), 'Batoca' or 'Trajadura' (syn. 'Treixadura') in _Vinhos Verdes_ regions or 'Fernao Pires' as the main white variety employed in the Bairrada Apellation, despite being also generally used in other Portuguese Apellations [5], making these white wines play an important economic role, with 'Alvarinho' and 'Loureiro' wines being mainly monovarietal ones [6]. In Galicia, the vineyard sector is of great economic importance, with a vineyard area of 24,000 ha and more than 194,000 wineries, with a total production of more than 800,000 hL, of which 300,000 hL is white wines [7]. Nowadays, the Galician wine sector is the most important one among the agro-industrial sectors, with around 20% of its total productionexported worldwide. Moreover, there has been a steady growth in average export costs from 2010 to 2019 [8]. Nowadays, global warming triggers earlier grape sugar ripening, generally unbalanced with aroma and flavor maturity, losing their potential acidity while the harvest is delayed for its aroma development [9]. Added to the fact that there is a highly competitive wine market, it is necessary to diversify products. The use of traditional varieties could help to preserve the genetic resources and to produce high-quality wines [10] elaborated in a sustainable agriculture [11]. Even though it is known that more than 6000 grapevine varieties exist over the world [12], only few of them cover the total world vineyard surface [13]. A deeper study of this varietal diversity could help to increase the varietal range of some appellations of origin regulations, which do not usually include minor varieties [14], despite some of them being able to offer high enological potential. Varieties, such as 'Godello', recently included in different Galician wine appellations of origin, have already achieved a high impact in worldwide wine evaluations [15]. New consumption requirements [14], as well as more extreme and demanding environmental conditions arising from climate change [16; 17], and multiple requests for the viticulture industry, such as globalization or economic factors [18], explain the necessity to study different grapevine varieties aiming to maintain a broad natural diversity and retain the wine regional typicity, as a way to respond to these risks to viticulture as we know it today. Aroma is one of the main factors that contribute to the quality and character of a wine [19], being the variety used highly related to that quality [20]. The aroma specific to the grape variety will become the varietal or primary aroma of the resulting wines, and despite only those varieties with a high terpene composition, such as Muscat ones, will produce odoriferous floral musts, most varieties that are non-muscat varieties or neutral ones could equally produce different wines with specific aroma characteristics linked to the specific variety [6]. The constitutive levels of volatile organic compounds (VOCs) of a vegetal species are highly dependent of genetics [21] and more specifically, at least in fruit, dependent on the cultivars [22], which is the reason why aroma could be a way to differentiate and characterize varieties. Nevertheless, other factors, such as supplementary irrigation [23], as well as the training system or the vineyard soil management [24; 25], could also affect the volatile composition.