Evaluation of Tannins and Anthocyanins in Marquette, Frontenac, and St. Croix Cold-Hardy Grape Cultivars

Cold-hardy grape cultivars have become popular in northern regions. Wines from these cultivars are low in tannins and lighter in color compared to Vitis vinifera. The northern regions are striving to enhance desired ″full body″ and red color qualities in the wine produced from cold-hardy grapes. The objective of this study was to compare tannin and pigment content in skins and seeds of three cold-hardy red grape cultivars, at two time points, from two locations, using the Adams-Harbertson (A-H) assay. The A-H assay is based on protein precipitation and spectrophotometry. Total tannin concentrations detected in Frontenac, Marquette, and St. Croix berries, ranged from 0.29 to 0.66 mg/berry catechin equivalents (CE). Bitter seed tannins were most abundant in Marquette berries (0.54 ± 0.66 mg/berry CE). Softer skin tannins were most abundant in St. Croix berries (0.24 ± 0.19 mg/berry CE). Monomeric anthocyanins contributed to over 60% of the total color at pH 4.9 and were highest in St. Croix skins (74.21% of the total color at pH 4.9). Varying amounts of short polymeric pigments and long polymeric pigments were present in grape skins, indicating that pigmented tannins had already formed by harvest. This is the first evaluation of tannins and pigments in Frontenac, Marquette, and St. Croix berries.