Influence of Potential Alcohol and pH Adjustment on Polyphenols and Sensory Characteristics of Red Wines Produced at Different Harvest Time Points

Abstract

Wine quality is influenced by grape maturity, typically monitored by measuring sugar content and acidity. However, environmental factors such as extreme weather or fungal infections can force winemakers to harvest earlier than desired. This study investigated whether sugar and pH adjustment used to increase potential alcohol and reduce the perception of acidity, can also compensate for immaturity in terms of phenolic extractability, composition, and related sensory attributes. Since anthocyanin and sugar accumulation profiles do not necessarily run parallel during grape ripening, it was important to study several harvest time points.
Wines were made from Pinot noir and Cabernet Sauvignon grapes harvested in 2019 at three different stages of grape maturity, in the range of 18-24 Brix. After bottling, phenolic analysis (HPLC-DAD/FD, LC-QToF-MS and spectrophotometry) and sensory evaluation revealed that adjustment of early-harvest must to pH 3.3 and 24.5 Brix enhanced the extraction of seed-associated phenolics such as monomeric catechins, and resulted in higher ratings of a green, herbaceous and ethereal aroma, rough astringency and a harsh mouthfeel. Adjustment did not significantly increase concentrations of skin-associated phenolics such as anthocyanins and polymeric pigments, and could therefore not compensate for a lack of color intensity. Wines made from the late-harvest grapes had significantly higher concentrations of anthocyanins and polymeric pigments and lower concentrations of monomeric catechins and procyanidins. This resulted in wines with a full body and high ratings in color intensity, dark fruit aroma, and smooth astringency. The data suggests that anthocyanins and polymeric pigments can be used as markers for grape maturity. Potential alcohol and pH adjustment could not change the phenolic composition and sensory perception of an early-harvest wine to mimic those of a late-harvest wine.