Volatile compounds in Amarone wines: occurrence, variability, and relationship with grape composition and vinification variables

Amarone della Valpolicella is one of the most important wines in the north of Italy, representing an important asset and a source of income and reputation for the region. Amarone is a rather unique example of dry red wine, as it is elaborated from withered grapes of varieties only grown locally, with its production regulation also imposing a minimum aging in oak of two years. These conditions result in specific wine aroma and flavor character. Most of the studies done on Amarone focused on aspects related to withering and therefore on grapes, especially Corvina, leaving a gap concerning the compositional characteristics of Amarone wine, as well as how the main key aspects of Amarone production influence its composition. The main objective of this thesis was to provide a comprehensive overview of the aroma composition of Amarone and to investigate the influence of the main technological processes applied in its production on key volatile compounds. To achieve this, the following methodology was implemented: first, the chemical and sensory characterization of commercial Amarone wines from vintage 2015 and 2016 was performed, including quantification of volatile compounds of different chemical classes and, in some cases, sensory assessment of their likely contribution to perceived Amarone odor. Second, the key technological steps of Amarone production, namely withering, fermentation, and aging were studied through a series of experiments to determine their impact on the formation of relevant aroma compounds in grapes and wines. For the first part, results showed that Amarone commercial wines were characterized by high odor impact of compounds such as of ethyl acetate, fruity esters, and β-damascenone. In addition, the existence of different ‘chemical styles’ within Amarone was highlighted, with some wines being characterized by high odor impact for compounds such as cineoles, ethyl phenols, DMS, and oak-related compounds. Some of these differences in chemical composition showed a good correspondence with the sensory data. The second part of the work was mainly focused on understanding the factors associated with the most relevant aroma compounds identified in the first part, with the aim of understanding the most influencing production variables. Withering was an important factor affecting key volatile compounds in both grapes and wines. Withering influenced positively the grape content of certain glycosidic precursors as well as of the terpene compound terpinen-4-ol, which appeared to be a key precursor to 1,4-cineole formation during aging. To this point, aging was a major factor in the development of key compounds such as DMS, cineoles, TDN, and TPB whose occurrence was mostly due to precursors presence. Finally, aspects related to fermentation also influenced the occurrence of these compounds. In the case of ethyl esters and ethyl acetate, grape composition, in particular YAN content, and yeast of choice influenced greatly. The present work provided an extensive characterization of Amarone wines and grapes, highlighting the key molecules that characterize their composition. In addition, in consideration of the complexity of Amarone wines, this thesis aimed to provide a framework to study the different technological steps which affect the formation of aroma compounds.