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Evaluating the Use of Shade Cloth on Wine Grapes

October 2017
by Jaime Lewis

San Luis Obispo, Calif.—In addition to the frenetic work of harvest, student intern Michael Overholt is busy conducting a research study to quantify the impact of shade cloth on vines at Tolosa Vineyards & Winery in San Luis Obispo County’s Edna Valley AVA. The study will follow specific blocks of vines and their fruit from véraison through harvest, vinification, pre- and post-bottling.

Overholt is a student at California Polytechnic State University, San Luis Obispo, working with Tolosa’s new winemaker, Fred Delivert, as well as Mesa Vineyard Management (which farms the vineyards) and viticulture consultant Randy Heinzen of Vineyard Professional Services to evaluate the effect of shade cloth on the evolution of grape maturity. The project is also under the academic oversight of two assistant professors at Cal Poly: Federico Casassa, Ph.D., and Jean Dodson Peterson, Ph.D.

Overholt said the idea for the study was born out of a Cal Poly class visit to Tolosa. The original concept was to uncover whether shade cloth creates better fruit and allows vines to reach maturity with less water.

“The goal of shade clothing is to decrease morning and early afternoon temperatures, lowering light exposure in the fruit zone,” Overholt wrote in the project proposal. “This results in delayed maturity and, potentially, increases in the concentration of aroma, aroma precursors, phenolic and other flavor compounds.”

Using Kestrel DROP wireless environmental data loggers placed throughout 12 regions (four trials with three regions per trial), Overholt monitors and aggregates the temperature, humidity and dew point with and without the coverage of shade cloth on both a plateau and a hillside of Tolosa’s 20-year-old Edna Ranch Vineyard.

The study samples from a total of 120 Pommard clone Pinot Noir vines at multiple milestones: véraison, véraison plus two weeks, véraison plus four weeks and harvest. Furthermore, Overholt and Delivert plan to partner to vinify the fruit from the trial blocks and evaluate the resulting wine chemically and with sensory analysis.

In an early presentation at Cal Poly, Overholt reported preliminary results from véraison and post- véraison stages of his research “indicate no clear effects of shade cloth on Brix, pH and TA. Fruit grown on the hillside showed lower acidity, potentially indicating higher light exposure.”

Yet grapes beneath the shade cloth on the plateau portion of the vineyard exhibited “reduced berry size as well as the proportion of solids, particularly seed weight.

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