Aroma chemical profiles characterization of wines produced with moristel grapes harvested at different time points

Abstract

The wine aroma is constituted by hundred of volatile chemical compounds that depend on many viticultural and oenological factors. One of the most important factors that will unequivocally affect the final wine pro-perties is the grape maturity level. Grape ripening is an extremely complex process, in which the metabolites and precursors concentrations change significantly with time. However, the knowledge of how grape ripe-ning affects wine aroma composition is still quite limited. Nowadays, wineries measure parameters such as sugar, pH, acidity and colorimetric tests to evaluate the degree of maturity of the vintage and decide the harvest data, but these analysis do not take into consideration the aromatic potential of the grape. The objective of the present work is to understand the differences in the aroma chemical profile of Moristel wines from different vineyards harvested at different time points. So, three different vineyards of Moris-tel grape variety in D.O. Somontano were selected, in two consecutive vintages: two in 2016 and one in 2017. Each block was harvested at different time points followed by microvinifications applying the same fermentation protocol. All of them have been elaborated in triplicated. This was assessed by the analysis of major aroma compounds (GC-FID), trace aroma compounds (GC-MS), methoxypyrazines (TD-GCxGC-MS), polyfunctionalmercaptans (SPE GC-MS), volatile sulfur compounds (BR-VSCs) and total acetaldehyde (HPLC-UV/VIS). The most important result is that the grapes harvested at 42 days postveraison, that is the “green” ones, pro-duce wines with high concentration of acetaldehyde and low IPT. Hence, low concentration of polyphenols facilitate the accumulation of this compound. Another reason for these acetaldehyde high concentrations could be problems associated with the lack of reduction factors (NADH or NADPH). This fact is also corroborated with the decreases of branched acid / fusel alcohol and branched ester/fu-sel alcohol ratios during the maturity. These facts can have very important sensory repercussion, the acetaldehyde and fusel alcohol are components of aroma buffer.

Finally, the evolution of certain maturity markers (c-3-hexenol, Y-nonalactona, rotundone) has been also observed, but these target compounds, by themselves, do not seem to have great sensory relevance in the final wines. This study has help to elucidate how grape maturity state contributes to final Moristel wine aroma profile and possible self-life.

Acknowledgements

This work has been funded by the Spanish MINECO (Project AGL2014-59840, RTC 2015-3379 and RTC-2016-4935-2) and partly co-funded by the European Union (FEDER). I.A. has re-ceived a grant from the Spanish FPU programs. Funding from D.G.A. (T53) and Fondo Social Europeo is acknowledged.