Evaluating Shade Cloths on Wine Grapes
Student intern, winemaker, and vineyard team track outcomes of minimizing late-season sun exposure
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 veraison through harvest, vinification, pre- and post-bottling.
Overholt is 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 California Polytechnic State University, San Luis Obispo: Federico Casassa, Ph.D., and Jean Dodson Peterson, Ph.D.
“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.”
Veraison through harvest
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 variety is Pinot Noir, Pommard clone, and the study samples from a total of 120 vines at multiple milestones: veraison, veraison plus two weeks, veraison plus four weeks, and at harvest, which is projected to take place mid- to late-September. 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 this week, Overholt reported preliminary results from veraison and post-veraison 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.”
In an email to Wines & Vines, Overholt added: “This is just in the beginning stages as we gather data from the vineyard, the different treatments and move into the winemaking stage shortly after harvest. The analysis and data retrieval will continue into wine chemistry with anthocyanins, phenolics/aromatic, tannins/mouthfeel, etc.”
Inspired by vineyard visit
Overholt said the idea for the study was born out of a Cal Poly class visit to Tolosa. “The vineyard manager was telling us a little about shade cloth and we were intrigued. He said they’d only been using it for a year and we asked, ‘What’s the data like on this?’”
When Overholt learned data hadn’t been recorded on the shade cloth’s effects, he worked with professors Cassasa and Dodson Peterson to draw up a proposal to collect it himself. “The original concept was, number one, does the shade cloth create better fruit? And, number two, given the fact that there’s a water shortage, not just here but everywhere in California, are you able to grow with less water?”
Overholt adds that canopy management is especially challenging with Pinot Noir vines that — taking into account rootstock and soil — don’t typically grow a large, vigorous canopy the way a variety like Syrah can, for instance.“So this was Tolosa’s idea,” he said, “to mitigate the water and irrigation issue and still be able to support a fruit zone where the grapes will grow more evenly.”
The principle of conducting proper trials appeals, in particular, to the scientific background of Tolosa’s new French-born winemaker, Delivert, who graduated from École Supérieure d’Agriculture de Purpan in Toulouse with a master’s degree in agricultural science in 1995. He came to Tolosa in July from Napa Valley where his career took him through the cellars of Far Niente, Duckhorn Vineyards and Hafner Vineyard; as assistant winemaker at PlumpJack and CADE; as winemaker at Martin Estate and Tuck Beckstoffer Wines; and, most recently, consulting for Clark-Claudon, Paon, Tamber Bey and S.R. Tonella Cellars.
“This is a pretty vertically-integrated study,” Delivert said of the Cal Poly shade cloth trials. “I have a scientific background so, for me, I would like to see the study run for two, three years; one year isn’t enough. I always say it takes five years for a winemaker to know the blocks. It makes sense for me to carry on that experimentation and validate the results for a few years.”
He added he is eager to work with Overholt on protocol, as well as provide space and some materials to conduct the research. “I really would like to see some strong bonds form between Tolosa and Cal Poly.”
