When it comes to wine the San Joaquin Valley is not the highly sought-after appellation other regions enjoy.

Long, hot summers do well to produce table and raisin grapes, but climate conditions are not as conducive to the popular varieties that tend to do better in cooler climates.

In an effort to perhaps put more value into the Valley’s grape industry, University of California researchers are studying over 50 different wine grape varieties to see which ones can produce the tonnage and quality necessary to profitably make quality wines.

The studies couldn’t come at a better time as the San Joaquin Valley grape industry has been challenged in recent years by lower returns, leading some to replace their vineyards with tree nuts because of their profitability.

Viticulture specialist Lindsay Jordan is one of the “new kids on the block” with the University of California Cooperative Extension. Shortly after she was hired in early 2015 to serve grape growers in the counties of Madera, Merced and Mariposa, she was handed a project started by now-retired farm advisor Jim Wolpert. That project is designed to test the performance of wine grape varieties under the long, hot summers of the San Joaquin Valley.

Jordan earned her graduate degree from Cornell University, where she studied horticulture and vineyard floor management in Riesling grapes in the Finger Lakes Region of upstate New York.

Jordan’s colleague, Cooperative Extension Specialist Matthew Fidelibus, passed along the study to Jordan after assuming it from Wolpert. She’s been running with it ever since.

Jordan is looking at 56 different varieties, split evenly between reds and whites, at the Kearney Agricultural Research and Extension Center near Fresno for a variety of traits that, at the very least, could become part of a blend program with the wineries.

“Growing for components are an attitude we can adopt, knowing that we’re going to use them in blends,” she said.

Popular varieties                                 

“We all know that cab is king,” she says of Cabernet Sauvignon. “The trick is it can struggle in the San Joaquin Valley heat to get the level of color and some of the aromas and flavors we like.”

Because of the high summer heat, cabs can quickly develop sugars without developing the colors necessary to make a good wine, she says.

Jordan is not discounting the possibility of grapes like Segalin or Teroldego as stand-alone varietals – experimental versions have been bottled by Constellation Winery’s research and development department in cooperation with the University of California.

Those or other varieties could make marketable stand-alone wines, or they could become part of a blend program as blends gain in popularity with consumers, Jordan says.

Still, some of the reds holding out promise in early studies include Teroldego clones, Triplett, Charbono clones, Sagrantino, Bonarda, Segalin, Morrastel, Marselan, Graciano and Pinotage. Those in bold appear to yield more than 10 tons per acre with less than 10 percent rot.

She calls Segalin her “color bomb,” as it does well to produce the color desired in a red wine. It also yields well, averaging 13.6 tons per acre over the past four years.

Wine-quality white varieties include: Fiano, Petit Manseng, Malvasia Bianca, Arinto, Erbaluce, Alvarinho, Biancu Gentile, Moscato Giallo, Falanghina, and Viozinho. Those in bold tend to yield over 10 tons per acre with less than 10 percent rot.

The study

The vineyard covers less than two acres at the Kearney Agricultural Center in Parlier. Summers there are hot with generally mild winter conditions. Humidity can sometimes be an issue in the summer.

Scions were grafted onto 1103P rootstock in 2009 (the rootstock was planted a year earlier). Since then some of the varieties that did poorly were removed and new scions were grafted onto the existing rootstock.

Jordan says she is using a more aggressive approach to deficit irrigating the vines than she suspect’s commercial growers may employ, or would recommend to them. She uses a pressure bomb and a device developed by Mark Battany, a viticulture advisor on the Central Coast, called “the Paso Panel.”

The Paso Panel is an inexpensive, do-it-yourself device that calculates the shaded area under the canopy, providing a cost-effective way of calculating crop coefficient and evapotranspiration.

Once she does turn on the water, vines generally receive about 65 percent of what they need.

Common pesticide applications are made as necessary. Fertilizers are not currently being used in the study.

Vines are shoot-thinned to two shoots per spur. In some cases she is mechanically pruning the vines to test their response.

Jordan is experimenting with mechanical pruning techniques, which she thinks could improve yields and decrease incidents of rot in vines that struggle with both.

In the cases where mechanical pruning takes place she has found the vines inherently leave more buds, which ultimately leads to more shoots and more fruit.

Mechanically-pruned vines tend to yield smaller clusters with looser berries.

“That’s a great way to help reduce rot,” she says.

Harvest is done by hand when the white varieties “are as close to 22 brix as I can get them,” she says. Red varieties are harvested with a brix of 24-25.

The outcome

Jordan is partnering with Constellation Brands wine, which is taking grapes from her study and turning them into wine at the company’s research and development center near Madera. As the trial continues, Constellation is paring down the different varieties as winemakers there look to make the best wines from the grapes provided.

Constellation selected 21 varieties in 2015 for small-lot wines.

Jordan has offered wine tastings at various industry events as she talks up what she continues to learn from the study.

She already has a list of the varieties that aren’t cutting it for various reasons. Some are highly prone to rot while others become raisins in the summer heat.

Peterangelo Vallis, executive director of the San Joaquin Valley Winegrowers Association, is optimistic about the studies.

“This has been a long-term project that has very good industry support,” he said.

At the end of the day Jordan says she is looking for varieties that can produce the tonnage with the kind of quality wineries need in their programs. She is also looking for vines that do not need considerable management.