(Wines&Vines) - Researchers from the University of California, Davis, began a trial this year at the Oakville Experimental Station in Napa Valley to evaluate the use of different colors of commercially available shade netting and its effects on grape cluster temperature and light exposure in relation to chemical and phenolic development and composition in grape berries. The trial is being conducted by viticulture extension specialist Dr. Kaan Kurtural and enology extension specialist Dr. Anita Oberholster (both of UC Davis).

The researchers discussed the trial during a recent field day held at the Oakville Station vineyard. One reason for interest in the use of shade netting is climate change. “As the climate is getting warmer, we’re seeing potentially different responses from plants to temperature and light,” Kurtural said. He also noted interest in better understanding chemical changes in grape berries during ripening to potentially better manage fruit quality for its contribution to wine astringency, color and flavor. 

Current knowledge and past shading trials

Oberholster, who participated in a vineyard shade trial in South Africa, said such trials are studying the effects of temperature and light quality and quantity and their interaction and impacts on grape phenolics during ripening. She explained some of the basic changes currently known to occur in berry chemistry during grape development and ripening. From berry set to véraison, there are increases in organic acids, amino acids, minerals, methoxypyrazines, hydroxycinnamic acids, and tannins. From véraison to harvest there are increases in anthocyanins, flavonols, sugars, monoterpenoids and norisoprenoids, and there are decreases in organic acids and methoxypyrazines.