Influence of the use of unripe grapes to reduce ethanol content and pH on the color, polyphenol and polysaccharide composition of conventional and hot macerated Pinot Noir and Tannat wines

The aim of this research was to determine the effectiveness of the substitution of grape juice of grapes with different maturation degree and prefermentative hot maceration to obtain Pinot Noir and Tannat red wines with lower alcohol content and pH and higher color and phenolic compound concentrations. Immature grape juice was extracted of grapes harvested in veraison and kept at 4 °C until its use. In technological maturity, the grapes harvested were destemmed, crushed and distributed in 12 containers per cultivar. Six were controls while in the other six 3 L of the original grape juice were substituted by 3 L of unripe grape juice. Next, three containers from each experimental group were traditionally macerated, while the other three were submitted to a prefermentative hot maceration (one hour at 60–70 °C). All treatments performed a fermentative maceration of 7 days. Wines produced from substituted musts had lower alcohol content (14% off) and pH (9% off) and higher titratable acidity (48% more), but no other important changes in wine components were detected. Prefermentative hot maceration increased wine color intensity (50%), total phenolic compounds (66%), total anthocyanin (42%), proanthocyanidin (65%) and polysaccharide (95%) concentrations. The joint consideration of both techniques is an interesting tool to simultaneously mitigate the problems caused by climate change with respect to the maturity of the grape and improve the color of the wine and its concentration in polysaccharides and phenolic compounds.