Sanliang Gu managed to finish harvesting his 2011 Cabernet Sauvignon grapes in time to enjoy Thanksgiving turkey with his family. Not in St. Helena in Napa Valley, but in Fresno.

No he was not harvesting Cabernet Sauvignon raisins as you might expect in California’s Central Valley, but wine grapes with quality equal to the cooler coastal climates of California.

Gu is a viticulturist in the California State University, Fresno viticulture and enology research center and for the past three years has practiced only what can be called draconian crop management in a portion of the Fresno State vineyard. His goal has been to achieve high quality San Joaquin Valley varietal wine grapes.

More than 60 percent of California’s wine grape production comes from the Central Valley; however, like Rodney Dangerfield, the valley gets no respect. Valley growers receive far less per ton for the same varietal grapes as other areas of the state. It’s not the fault of the growers. It’s the weather. It is simply too warm to product premium wine grapes. Grapes ripen too quickly under the valley sun.

Gu at the recent CSUF Grape Day detailed how he manipulated the vines to match the weather by shifting the ripening of the grape from the warmest time of the year to the coolest. He did it by stripping the vines of all clusters, leaves and laterals in June and July, leaving only six nodes on the growing shoots.

He basically dropped a summer crop in return for a fall crop.

“High temperatures often inhibit the accumulation and increase the degredation of organic acids, anthocyanins, tannins and phenolics, resulting in wines high in pH, low acidity, less intense color,” Gu reports.

In shifting fruit ripening from July and August to October through early November, Gu reports smaller berries, lower pH, higher titratible acidity and higher content of skin anthocyanins, tannins and total phenolics.

By moving the ripening to late fall, Gu lengthened the time from veraison to harvest from 40 days to 60 days with fewer degree day hours above 77 degrees and more degree hours below 77.

Temperature, he says, is the most influential factor in determining fruit acidity, color and flavor constituents.

All this is to say that the quality of the grapes improved in the late harvest from what Gu calls “crop forcing.” He did it without sacrificing in fall harvested grapes compared to summer harvested grapes.

Unconventional approach

Gu calls his approach to improving the quality of San Joaquin Valley wine grapes “unconventional.” That is an understatement. “Some people do not believe what we are doing and some get really excited and want to try it,” Gu says.

Gu is proving academically it can be done. The questions are is the wine better and is it economical to do?

He has not made commercial wine from the crop forced grapes, but says that is the next step along with an economic analysis of the crop stripping.

While Gu’s vine summer stripping has been done by hand, which is very expensive, Fresno State operates a wide array of commercial machinery on other research trials that can strip leaves and bunches off vines. He said mechanization is the next step in his unorthodox research approach.

Gu said an economist is joining in the research effort this year to see if this “makes sense economically at what price points.”

There is a huge disparity over wine grape prices from the valley to the coastal area. The valley’s Cabernet Sauvignon crop brought $485 per ton last year compared to more than $2,000 per ton for Cabernet Sauvignon from Sonoma County and almost $950 per ton from Monterey County.

The quality of valley grapes can be improved dramatically. The question is will wineries pay for it?

Gu’s work is not just about quality. He points out that crop forcing could be used when a grower loses a crop to frost when primary clusters are destroyed. It could also be used to open up even warmer regions of the state to premium wine grape production.