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 A
scientist from Fresno State’s Viticulture and Enology Research Center (VERC)
will soon join the “hang time” debate with San Joaquin Valley wine grape
growers.
Viticulture research specialist Dr. Sanliang Gu is examining several
“regulated deficit irrigation” (RDI) strategies using extended hang time
in a study to determine how the methods affect quality and color of
grapes grown for wine in the valley.
Hang time refers to that point at which the grapes are ready for harvest
but are allowed to “hang” a few days longer, resulting in increased
sugar content and further accumulation of acids and color, Gu said in
explaining his research. The right combination of these characteristics
can make for a successful fermentation and outstanding wine. A hang time
that’s too long can result in grapes with a sugar content that’s too
high, prompting sluggish or “stuck” fermentations and a significant loss
of wine quality.
Grower opinions on hang time vary from being “required” for better wine
quality regardless of variety, location, and vintage, to it being
absolutely unnecessary, with only negative impacts on fruit quality and
vine health, Gu noted.
The debate continues because relatively little research has been done in
the San Joaquin Valley to determine the relationship between hang time,
fruit quality and vine health, Gu said. One reason is because premium
wine grape growing is relatively new to the Valley, and summer weather
conditions here can make hang time management especially challenging.
 “Under
the stressful temperatures and humidity conditions during and beyond the
ripening period, hang time may negatively impact the grapevine’s
capacity and functionality the most in this region, especially under
regulated deficit irrigation, which has become a common management
practice throughout the wine grape industry in California,” Gu said. “We
need to find a management strategy to synchronize the sugar accumulation
and color-flavor development to improve fruit quality and minimize or
eliminate the need of hang time.”
Gu’s goal is to maximize fruit sugar development with color and flavor
using regulated deficit irrigation, using a minimum amount of hang time,
this avoiding damage to the vines.
The experiment is being conducted in two locations: a 10-acre vineyard
of Cabernet Sauvignon on Fresno State’s university farm, and a 75-acre
block of Syrah farmed by a cooperating grower in the Fresno area.
Treatments will include conventional drip and regulated deficit
irrigation.
The deficit irrigation treatment will be conducted using information
based on weather conditions, soil moisture and vine vigor. Trials will
include the use of a pioneering computer-based technology that will
govern the irrigation system. The goal will be to reduce water use by 30
percent to 60 percent of conventional irrigation practices, Gu said.
In combination with the deficit irrigation treatments, three hang time
treatments will be used: grapes will be harvested at 24 degrees on the
Brix scale, which is a conventional harvest date; at two weeks after
conventional harvest date, or at 28 Brix; and fruit not harvested.
Regulated deficit irrigation offers other benefits in addition to
potentially better wine quality, Gu noted.
“A reduction in water use means less electricity needed to pump water
and pressurize the irrigation system, and therefore represents an
economic incentive for the grower. In addition, when managed properly,
RDI results in less shoot growth and generally more open canopies that
increase the exposure in the fruit zone to sunlight and air movement,”
Gu said. “This exposure results in better fruit color and flavors, while
decreasing the potential for diseases and pests.”
Results of the study will help to answer questions and concerns about
hang time with sound scientific research and justification for the
practice of hang time. Gu anticipates release of results and analysis
next year. Overseeing the study, along with Gu, is VERC director Robert
Wample.
For more information on the project, Gu may be contacted at
sanliang@csufresno.edu.
(Copy by Steve Olson of the
California Agricultural Technology Institute at Fresno State.)
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