Off-vine grape dehydration process under controlled conditions: effect on organic acid content of musts and wines

Abstract

Off-vine grape dehydration under controlled conditions is a pre-fermentative process which could be used independently of the climatic conditions of the wine region and leads to changes in the chemical composition of grapes. The aim of this study was to evaluate the effect of grape dehydration process under controlled environment conditions on the organic acids composition of musts and wines. The 'Cabernet Sauvignon' grapes were harvested (20±1 °Brix) and placed to dehydration under controlled conditions (7°C and 35% relative humidity, 12 m3 s-1 of airflow). Must samples were prepared with non-dehydrated grapes (control samples) and after the grapes reached the drying of 10, 20, 30 and 40%, the musts were submitted to the same vinification condition to obtain the wine samples. The following organic acids, tartaric, malic, lactic, citric, succinic and acetic were determined by liquid chromatography using isocratic elution and with detection at 212 nm. The results showed that tartaric, malic and citric acids were detected in all musts studied. The musts obtained from grapes dehydrated by 20, 30 and 40 also showed contents of succinic acid (2.38, 2.57 and 4.83 g L-1 respectively) and acetic acid was detected only in the must obtained from dried grape of 40% (0.61 g L-1). It was observed that musts obtained from dried grapes showed high concentrations of organic acids according to the percentages of dehydration applied to the grapes. The tartaric, malic, citric and succinic acids were detected in all wines, and the wines obtained from 30 and 40% dried grapes also showed concentrations of lactic acid (0.34-0.80 g L-1 respectively) and acetic acid (0.24-0.93 g L-1 respectively). These results demonstrate that off-vine grape dehydration process under controlled conditions modifies the organic acid composition of the must and wines.