Late-Season Source Limitation Practices to Delay Ripening and Improve Color of Cabernet Sauvignon Grapes and Wine
Guadalupe Partida, Luca Brillante,* Miguel
Pedroza, Khushwinder Singh, and Kaylah Vasquez
*Department of Viticulture and Enology, California State
University Fresno, 2360 E Barstow Ave, Fresno, CA, 93740
(lucabrillante@csufresno.edu)
Recent increased temperatures are accelerating grape ripening, leading to unbalanced wines with high alcohol content, but poor aroma and phenolic composition. Late-season canopy manipulation practices to reduce the size of the photosynthetic apparatus after veraison can delay technological ripeness in cool climates. These methods have not been tested in areas with high irradiance and temperature, where berry composition is negatively affected from late fruit exposure. In this Cabernet Sauvignon trial, we compared the application of an antitranspirant (pinolene) to severe canopy topping and above-bunch zone leaf removal, all performed during late stages of ripening, with an untouched control. We monitored the vines weekly by measuring stem water potential, gas exchange, and fruit zone light exposure. We sampled berries to measure berry weight, total soluble solids, pH, titratable acidity, and the anthocyanin profile. At harvest, we assessed yield components, measured carbon isotope discrimination, rated sunburn on clusters, and produced experimental wines. We submitted harvest samples to metabolomic profiling through PFP-Q Exactive MS/MS and wines to sensory analysis. Application of the antitranspirant significantly reduced stomatal conductance and assimilation rate, but did not affect stem water potential. Inversely, leaf removal and topping increased water potential, but did not affect leaf gas exchange. Late topping was the only treatment that decreased sugar content (up to 2 Brix), increase titratable acidity and pH, and improve anthocyanin content, because of less degradation of di-hydroxylated forms. Late leaf removal above the bunch zone increased lightning conditions in the canopy and produced the most significant damage on fruits. Yield components were not affected. This work suggests that late-season canopy management can effectively control ripening speed and improve grapes and wines. Still, the effect on grape exposure in a critical time must be well-balanced to avoid problems with the appropriate technique.
Funding Support: n/a
