Seminar - Regional Variability in the Phenolic Chemistry, Tannin Extractability, and Cell Wall Composition of Pennsylvania Vitis Vinifera and Interspecific Hybrid Red Wine Grapes

Interpecific hybrid wine grapes are commonly grown in Pennsylvania because of their cold hardiness and resistance to common pests and diseases. The quality of wine made from hybrid grapes is adversely affected by a deficiency in extracted tannins. Grape cell-wall material (CWM) is implicated in this quality defect. However, the relationship between CWM composition and tannin extractability remains poorly understood. Grape and wine quality is heavily influenced by the grapevine environment. Previous research has investigated the effect of environmental variables on Vitis vinifera cultivars grown in a Mediterranean climate. However, it is unknown how these results may apply to hybrid grapes grown in a cool-climate region like Pennsylvania. Experiments were conducted on Chambourcin (hybrid) and Cabernet Franc (V. vinifera) grapes sourced from 4 locations within Pennsylvania and across 3 vintages. Model tannin extractions and microvinification experiments showed a 4.2-fold difference in final wine tannin content across locations. Differences between cultivars only appeared in tannin content measured after pressing and racking, indicating that post-press tannin losses may be responsible for hybrid tannin deficiencies. Tannin extractability characteristics were negatively correlated with growing season precipitation. CWM analysis revealed higher tannin binding by loosely bound polysaccharides from hybrid grapes. UHPLC-MS analysis of grape extracts revealed both a strong effect of vintage and a relatively weak effect of location on the grape nonvolatile metabolome. Significant differences were noted in anthocyanins, organic acids, and flavonoids likely to impact the sensory profile of the final wine. In summary, this research demonstrated a strong effect of grapevine environment on grape and wine chemistry. Growing season precipitation and post-press tannin losses were identified as major contributors to hybrid wine tannin deficiencies.

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