Effect of harvest date on the aroma of merlot and Cabernet-Sauvignon musts and wines: analytical and sensory approaches

Abstract

The aromas found in young red wines of Merlot and Cabernet sauvignon (found in the Bordeaux region) suggest a complex mixture of odours of fresh red fruits such as cherry or blackberry for Merlot, and strawberry or blackcurrant for Cabernet sauvignon. The aromas of these wines are strongly linked with the maturity of the grapes. Climate change that occurred during the last decade in Bordeaux has induced changes in the ripening conditions of grape berries. It has been empirically admitted that overripening of the berries during hot and dry summers results in the development of characteristic shade of aromas of cooked fruits (fig, prune). These aromas are being found in both young wines and musts. To date, the chemical compounds responsible for these cooked fruit aromas are still unidentified. Therefore, it seemed essential to identify and assay these molecular markers. Gas chromatography coupled with olfactometry and mass spectrometry (GC-O-MS) was used in order to identify volatile compounds responsible for the cooked fruit odour in Merlot and Cabernet Sauvignon (CS) grapes. Same techniques were used to follow the development of these compounds during the maturation of the berries. As a result, different odorous zones of cooked fruits have been highlighted and identified by GC-MS. First presented results refer to the evolution of these compounds during ripening and overripening of CS grapes in laboratory-controlled conditions and in a plot of vines (Vintage 2012, Pauillac appellation) harvested in three harvest dates spaced of 4 days. In the climate conditions of this vintage it was found that a 4 days delay according to the optimal harvest date does not modify pH and sugar amounts; on the other hand, aromatic compound contents are modified and total acidity decrease. Shade of cooked fruity aromas appear and are detected during sensory evaluation.