Evolution of grape aromatic composition in cv. Ugni blanc

Abstract

AIM: Cognac is a protected appellation of origin where world-famous brandies are produced. These brandies are obtained by the traditional double distillation of wines from Ugni blanc cultivar, which is the main variety planted. According to the Cognac Appellation, harvest can occur between 13 & 21 °Brix. To date the harvest is assessed by vine growers only by sugar & acidity ripeness without considering the evolution of the aromatic profile. Hence, the goal of this research is to study the behavior of the main volatile compounds of grapes in order to better conduct the harvest.

METHODS: Two vineyard plots during two consecutive vintages (2019, 2020) were used to collect different fractions of 30 whole bunches. The samples were collected every week from pea-size to over ripeness (>21 °Brix) and then were stored at – 40°C until further analysis. Berries were grounded according to the protocol as described in Poitou, 2016. Grape powder were obtained and then analyzed for free & total volatiles by SPME-GC/MS (Young et al. 2015 ; Poitou, 2016). Principal component analysis (PCA) was conducted on the means of all significantly different parameters to elucidate the differences between grapes according to the maturity stage (Agilent MassProfiler Pro).

RESULTS: The kinetics of the volatile compounds during maturation showed strong variations with multiple trends depending the stage. Linear increase (e.g β-damascenone) or decrease (e.g p-cymene) of volatiles and a peak for cis-3-hexenol at véraison were found. Similarly to previous studies (Poitou, 2016 ; Ferrari et al. 2012), aromatic compounds were found to exhibit the same pattern. According to Rosillo et al. 1999, Ugni blanc & Chardonnay presents similar aromatic properties with low concentration of monoterpenes. Finally, the analysis of total volatiles showed the presence of newly identified terpenes in Ugni blanc grapes.

CONCLUSION

These results gave new insights for Ugni blanc aromatic characterization. Identification of terpenes with the total volatile method concludes that they are in their glycosylated form in grapes. Thus, they may be released during fermentation or distillation and participate to the aromatic complexity of wine distillates. With climate change, sugar concentration is expected to increase and will decouple sugar/acidity balance and the aromatic maturity. Therefore, understanding the aromatic maturity of Ugni Blanc will help growers to adapt their harvest date.