What is the contribution of stored organic acids as substrate for respiration and ethanolic fermentation in grape berry during ripening?

In 2004, in central Italy, a study was carried out to determine what contribution stored malate could make to the substrate utilised by respiration and ethanolic fermentation in grape berries, of the cultivar Pinot noir and Sagrantino, during ripening. Throughout berry development, periodically, the amount of malate was determined along with the amount of CO2 that was released by the berry. This allowed to estimate the contribution that stored malate could make to the substrate requirements of respiration and ethanolic fermentation of grape berries. It was found that this contribution was related to the stage of ripening. It was potentially high soon after veraison (beginning of ripening), whereas it was relatively low for the rest of ripening. Therefore, stored malate was not the quantitatively most important substrate utilised by respiration and ethanolic fermentation in the berries during most of ripening. It is likely that sugars provide the deficit in substrate. In addition, it was found that the increase in the respiratory quotient in the berries, during most of ripening, was not due to the use of malate as main respiratory substrate. The potential contribution of malate as substrates for respiration and ethanolic fermentation differed among cultivars.