Phenolic Extraction From Red Hybrid Winegrapes

Abstract

As the wine industry continues to expand, it has included rapid growth in the development of cool climate wine regions across the United States. This growth has been spurred by the use of native and hybrid winegrapes, along with the development of new hybrid cultivars for which there is little working experience. Research efforts, along with many consumers, have focused on Vitis vinifera based wines. A great many studies have concentrated on the viticultural and oenological management of phenolics, attempting by manipulation to enhance or suppress certain phenolic characteristics across many V. vinifera cultivars. While V. vinifera cultivars have a greater economic impact globally, the local use of cold hardy winegrapes can profoundly affect tourism and customer knowledge in particular regions. As tourism is driven by consumers, it is of paramount importance that winemakers produce salable wines using the resources available to them, including regionally adapted cultivars, tools, and techniques to best create a pleasurable wine experience. This research sought to assess the challenges winemakers face when using red hybrid winegrapes, and the ways that winemaking techniques influence the phenolic profile of hybrid cultivars Corot noir, Maréchal Foch, and Marquette. To gauge current production practices, a survey was distributed to winemakers in Michigan, Minnesota, New York, Pennsylvania, and Wisconsin, asking them to characterize their techniques and challenges in using red hybrid grapes for wine production. Statistical analyses of the survey data showed that winemakers deal primarily with challenges in acidity, phenolics, and storage. A multinomial logit model was fit to the data to estimate the likelihood of a winemaker encountering particular challenges based on winery size, location (state), and varietal use. Grapes were vinified in triplicate lots for each treatment of Corot noir and Maréchal Foch, and in duplicate lots for each treatment of Marquette, following standardized winemaking protocols. The five treatments investigated were as follows: control, enzyme addition, exogenous tannin addition, cold soak, and hot press. These treatments were chosen based on survey data to provide winemakers with scientific research on the grapes they use, instead of relying on data used for vinifera wines. Grape musts and wines were analyzed via HPLC to quantify and compare differences in phenolic concentration for each winemaking technique. Statistical analyses of the phenolic concentration data showed significant differences between treatments in Maréchal Foch musts and wines in the total tannin concentration, total monomeric concentration, and total anthocyanin concentration, though no significant differences were found between treatments for the mean degree of polymerization (mDP). Corot noir treatments showed no significant differences in the total concentration of monomeric phenolics, but statistically significant differences were found in anthocyanins, tannins, and the mDP, mostly between the hot press and tannin addition treatments. Few significant differences were found among treatments in the Marquette musts and wines.