Influences of pre- and post-veraison cluster thinning treatments on grape composition variables and monoterpene levels of Vitis vinifera L. cv. Sauvignon Blanc

Abstract

Grape composition plays important role for wine grapes in terms of wine grape quality. Besides, monoterpenes are a chemical class of compounds present in many highly aromatic Vitis vinifera L. cultivars belonging to Muscat family and some other special cultivars. One of these special grape cultivars is Sauvignon Blanc, and in this study, cluster thinning and its treatment times were used for a tool to increase quality attributes of cv. Sauvignon Blanc. The effects of cluster thinning times at different stages of berry development [B+4W (Bloom +4 Week), B+6W (Bloom +6 Week), B+8W (Bloom +8 Week), B+ 10W (Bloom + 10 Week) and B+ 12W (Bloom +12 Week)] on grape quality and yield components of cv. Sauvignon Blanc grapevines were investigated during the vegetation period of year 2008. Crop reduction by cluster thinning was roughly 37.5% in yield per grapevine. Grape composition characteristics (FVT (free volatile terpenes), PVT (potentially volatile terpenes), TSS (total soluble solids), TA (total acidity), pH, contents of K+ and Na+) and yield components (berry width, berry length, berry weight, cluster width, cluster length, cluster weight) were variously influenced by cluster thinning times. Canopy density as measured by point quadrat analysis differed among the cluster-thinned grapevines at different thinning times. In spite of differences in canopy density and cluster thinning times, grape composition and yield attributes were not statistically found to be significant except juice pH. Between pre- and post-veraison treatments, cluster thinning at B+8W especially improved grape quality characteristics of cv. Sauvignon Blanc.