Breeding for Quality in Grapes

Quality parameters that wine grape breeders must be concerned with include content of sugars, acids, anthocyanins and other phenolic compounds and a host of compounds that contribute to aroma and flavor of a wine. Some of these traits are far more tractable for breeding than others, though they are not necessarily easy to attain in all germplasm. Sugar and acid content are fairly easy to measure and target levels are well defined for breeders by winemakers’ preferences or limitations of yeast strains,  Anthocyanins and other phenolic compounds are somewhat more difficult to assay and their roles and interactions in determining wine quality are not as well understood. Defining breeding targets for these compounds is further complicated as their levels and form can change substantially with fermentation and aging of a wine.  The most difficult challenge is to select for flavor and aroma.  Wine flavor and aroma for a given genotype can vary depending on grape growing environment and wine production practices.  Information on the type, number, levels and interactions of flavor compounds is still not well understood in grape by enologists and flavor chemists. Variation in human sensitivity to individual or interacting compounds further complicates breeding for flavor. The interaction of these multiple factors affecting flavor can result in significant higher order interactions such as genotype x growing environment x winemaking practice x consumer preference/sensitivity that can greatly hamper evaluation and breeding progress.