Use of unripe grape wine as a tool for reducing alcohol content and improving the quality and oenological characteristics of red wines

In Mediterranean viticulture, climatic conditions are the main factors that determine grape composition and wine quality. Global warming is causing an increase in the accumulation of soluble solids in grapes, leading to early harvests that result in wines with high alcohol and low phenolic content and colour intensity. The aim of this research was to determine the effectiveness of mixing wines vinified from grapes with different maturation degrees from two consecutive vintages (2018 and 2019) in order to obtain wines with lower pH, lower alcohol content and higher phenolic compound concentration. The wine obtained after mixing wine from unripe grapes (URG) with second harvest (H2) wines significantly improved the physicochemical, chromatic and phenolic characteristics compared to the first harvest (H1) wine. On the other hand, the URGH2 wine had significantly lower alcohol content and pH and higher titratable acidity than the H2 wine. URGH2 maintained its colour intensity in both years and similar values of anthocyanin and tannin in 2018 compared to H2. All the wines were subjected to sensory analysis and the panelists were able to differentiate the wines in a triangle sensory test; the URGH2 wine was preferred in both years. These results show that the blend of unripe grape with wines from technologically mature grapes to reduce alcohol content and improve wine colour could be a useful tool for mitigating the problems caused by global warming in a warm and semiarid Mediterranean climate.