Smorgasbord of latest research from Grape Day

Smorgasbord of latest research from Grape Day

The tricky balancing act of applying just enough water while keeping an eye on mechanization that can save labor costs has probably never become more important than this season in the Central Valley of California.

The tricky balancing act of applying just enough water while keeping an eye on mechanization that can save labor costs has probably never become more important than this season in the Central Valley of California.

No wonder then that a field day at Fresno State drew scores of growers and others interested in bettering prospects in a time of drought and other challenges.

The event was Grape Day 2014, presented in August by the Department of Viticulture and Enology at Fresno State. It included a wide array of topics - from a look at new varieties of raisin rootstocks, the role of potassium in table grape quality, and quantification of rot in wine grapes.

Speakers for a variety of research trials discussed sustained and reduced deficit irrigation may have resulted in smaller grapes but satisfactory yield and pleasing attributes for wine grapes.

They included S. Kaan Kurtural, Bronco Wine Company Viticulture Chair and faculty member at Fresno State, who addressed cost savings through mechanization and the importance of canopy management.

Remarks from Kurtural and others centered on the need to let the sun shine in, to keep canopy growth under control to improve the quality of grapes, while at the same time ensuring high yield.

Maximize revenues

At Fresno State, a research plot has been set aside to look at how the industry can maximize revenues by mechanization that can cut labor costs while maintaining quality and the attributes of wine that shoppers seek.

Kurtural showcased equipment used to prune vines, while graduate student Michael Cook showed equipment to remove leaves in the vineyard.

Savings in labor costs can range between 70 percent and 80 percent, Kurtural said, but added it “takes training” on how to train vines.

Cook said pre-bloom leaf removal and reduced deficit irrigation appeared to have the best results for wine grapes in a research trial he conducted. Post-set leaf removal requires more input, he said, and the pre-bloom approach only required one pass.

He used a Clemons EL-50 in Stanislaus County for his research to open an 18-inch window in the fruiting zone. He quantified the effects that had on phenolic compounds in the grapes.

Cook said “unbalanced” vines with large and dense canopies are an issue in the Central Valley and mechanized leaf removal and deficit irrigation may be a solution.

Raisin rootstocks

Matthew Fidelibus, extension specialist with the University of California at Davis, talked of the development of new rootstocks for raisin grapes. None has been adopted in 45 years, he said, since Harmony and Freedom became mainstays, and strains of root nematodes that can overcome the resistance of those two rootstocks have evolved.

As water becomes more limited, Fidelibus said, the need for drought and salt tolerant rootstocks will increase.

He said efforts are underway to develop only a few alternative rootstocks since “too many choices often results in people delaying in choosing.”
Researcher Peter Cousins is among those who are looking at alternative rootstocks. Some of a half dozen being tested are marginal to deficient in taking up such important nutrients as potassium and nitrogen.

For instance, 1103-P takes up less nitrogen, and Illinois 547-1 takes up more sodium and has lower yields.

Higher mold preferred

Roy Thornton, a faculty member with the Department of Viticulture and Enology, and Susan Rodriguez, a lecturer and research fellow with the department, are looking at ways to determine the amount of rot in wine grapes.

Interestingly, Rodriguez discovered that some tasters of wine prefer Zinfandel wine with a higher level of mold.

The California Winegrape Inspection Advisory Board allows 2 percent rot in wine grapes, and Rodriguez sought to learn at what level moldy grapes would wine taste or smell different. This level was determined in a sensory laboratory to be at 4 percent in Chardonnay, 12 percent in Zinfandel.

Tests conducted by researchers at Fresno State came up with mold or rot calibrations similar to those that emerged at a sugar stand where truckloads of juiced grapes were tested in Livingston.

Sonet Van Zyl, a faculty member, Fresno State Department of Viticulture and Enology, discussed the effects of foliar potassium applications on table grape quality.

She found that potassium caused significant increases in soluble solids in Autumn Royal and Scarlet Royal grapes and accelerated maturity. Early or late ripening is preferred for higher prices, Van Zyl said.

Potassium increases sugar, starch and color accumulation, Van Zyl said. The best sources of potassium are potassium sorbate, potassium bicarbonate and Metalosate potassium.

Clusters were dipped to accelerate maturity.

Ideal harvest date

Hend Letaief, a faculty member with the Department of Viticulture and Enology, looked at ways to predict the ideal harvest date by measuring seed texture.

Harvesting wine grapes at the optimum level of maturity is a key to making good wine, Letaief said.

Mature seeds, she said, will yield a smaller amount of bitter and harsh tannins in a maceration tank.

Letaief said instrumental texture analysis gives a consistent description of the ripening process.  Depending upon the climatic conditions and soil type, she said, grape seeds could reach their optimal “textural” maturity up to two weeks before commercial harvest.

Compression tests were used to determine seed hardness and other attributes. Seed stiffness was deemed “the most interesting texture parameter,” she said.

Jamal Rayyis, an internationally-noted writer and wine critic, was the keynote speaker, offering an educational wine sampling.

Rayyis wrote several editions of Food and Wine Magazine's Wine Guide from 2002- 2008.

He talked of the history of the state’s and Valley’s wine production, and drew some comparisons between the Valley and a major wine production region in the south of France that is also a “bulk wine” producer.

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