Ripening profile of grape berry acids and sugars in University of Minnesota wine grape cultivars, select vitis vinifera, and other hybrid cultivars

Abstract

Recent introduction of new cold-hardy grape (<italic>Vitis sp.</italic>) cultivars has fueled a growing wine industry in non-traditional temperate growing regions. Though widely grown, little is known of the chemical composition of the cold-hardy wine grape cultivars. To develop a profile of the ripening process and quantify key grape berry metabolites, chemical analyses were performed on University of Minnesota wine grape cultivars, select <italic>V. vinifera</italic> cultivars, and other hybrid cultivars throughout fruit ripening. Organic acid and sugar concentrations of the eleven wine grape cultivars were determined using liquid chromatography/ mass spectrometry (LC/MS). All cultivars maintained glucose to fructose ratio of approximately 1:1 ratio and tartaric to malic ratio varied between years and cultivars. Cold-hardy wine grape cultivars `Frontenac', `Frontenac gris', and `La Crescent' retain higher concentrations of organic acids throughout berry development. Year was found to have little or no effect on malic or tartaric acid concentrations. Soluble solids content (SSC), titratable acidity (TA), pH and berry weight measurements were taken for three consecutive years (2010-2012). TA and pH profiles varied substantially among the years. TA, SSC, and pH were compared to growing degree days (GDD) to determine the number of heat units needed to ripen the selected cultivars and investigate if GDD is a valid predictor for grape maturity. Cold-hardy hybrid need approximately 1,400 GDD&#730;C to ripen fruit in Minnesota. GDD was found to be useful in predicting grape berry maturity especially SSC levels.