Posts Tagged: Grapes
Study shows sugar, color content should be watched
Warming temperatures over the past 60 years have led to increased wine quality, but a new study looking at sugar and color content in grapes indicates the industry may be facing trouble if trends continue, according to collaborative research out of the University of California, Davis, and University of Bordeaux.
“Quality has increased steadily up to now,” said lead author Kaan Kurtural, a professor of viticulture and enology and an extension specialist at UC Davis. “We just don't know the tipping point.”
Kurtural's research, published in the journal OENO One, focuses on two renowned wine regions — Napa Valley and Bordeaux, France.
Researchers looked at ripening, grape quality and temperature data over six decades in both regions and then confirmed the findings with a five-year trial in Napa. They also consulted wine ratings in publications like Wine Spectator to gauge consumer demand.
One key finding: As temperatures exceeded what was considered the optimal level for quality, the grapes produced better wines.
“Previous research had few field data, but a record of assumptions,” said Kurtural.
Other quality factors at play
Temperature is a factor, but the paper suggests that sugar and color content should not be discounted. The authors also identified a biomarker that affects taste, color and other factors that can be the bellwether for climate change in red-skinned wine grapes.
“Temperature is always there,” he said. “Temperature is not your bellwether.”
Higher temperatures can harm grape composition, including color, taste and aroma. Researchers examined pigment and sugar content of five California vintages of cabernet sauvignon, finding that as the grapes got sweeter the skin and color deteriorated.
The degradation of these quality-related compounds and the observed plateaus of wine quality ratings suggests there can be too much of a good thing.
Researchers have long theorized that increasing temperatures from climate change would lead to shifts in wine-growing regions, opening up some new areas for vineyards and making others unsustainable.
That shift could be a boon to some economies and devastating to others, something the industry should watch.
“Since the 1980s, grapes got riper and they were able to make better flavor and color compounds,” Kurtural said. “Are we going to lose this or adapt more?”
Gregory A. Gambetta with the University of Bordeaux is a corresponding author on the paper.
For more information:
- Kaan Kurtural, Viticulture and Enology, cell 707-200-5378, email@example.com
- Amy Quinton, UC Davis News and Media Relations, cell 530-601-8077, firstname.lastname@example.org
- Emily C. Dooley, College of Agricultural and Environmental Sciences, cell 530-650-6807, email@example.com
Study finds using less doesn't compromise quality
California grape growers in coastal areas can use less water during times of drought and cut irrigation levels without affecting crop yields or quality, according to a new study out of the University of California, Davis.
The findings, published today (Sept. 1) in the journal Frontiers in Plant Science, show that vineyards can use 50% of the irrigation water normally used by grape crops without compromising flavor, color and sugar content.
It sheds new light on how vineyards can mitigate drought effects at a time when California is experiencing a severe water shortage and facing more extreme weather brought on by climate change, according to lead author Kaan Kurtural, professor of viticulture and enology and an extension specialist at UC Davis.
“It is a significant finding,” Kurtural said. “We don't necessarily have to increase the amount of water supplied to grape vines.”
Growers will also be able to use this information to plan for the next growing season. “Everybody's worried about what's going to happen next year,” he said.
Kurtural and others from his lab studied irrigation and cabernet sauvignon grape quality at a research vineyard in Napa Valley over two growing seasons, a rainy one in 2019 and a hyper-arid one in 2020.
They focused on crop evapotranspiration, which was the amount of water lost to the atmosphere from the vineyard system based on canopy size. The weekly tests used irrigation to replace 25%, 50% and 100% of what had been lost by the crop to evapotranspiration.
Researchers found that replacing 50% of the water was the most beneficial in maintaining the grape's flavor profile and yield. The level of symbiotic arbuscular mycorrhizal fungi, which help grapevines overcome stresses such as water deficits, was also not compromised. And the water used to dilute nitrogen application was also reduced, making the process more environmentally friendly.
The water footprint for growing grapes also decreased. For both the 25% and 50% replacement levels, water use efficiency increased between 18.6% and 29.2% in the 2019 growing season and by 29.2% and 42.9% in the following dry year.
While focused on cabernet sauvignon, most red grapes will respond similarly, he said.
“In the end, drought is not coming for wine,” Kurtural said. “There doesn't need to be a tremendous amount of water for grapes. If you over irrigate in times like these, you're just going to ruin quality for little gain.”
Members of Kurtural's lab — Nazareth Torres, Runze Yu, Johann Martinez-Lüscher and Evmorefia Kostaki — are also credited as authors.
University of California Agriculture and Natural Resources provided partial funding.
For more information, contact:
- Kaan Kurtural, Viticulture and Enology, firstname.lastname@example.org
- Amy Quinton, UC Davis News and Media Relations, email@example.com
- Emily C. Dooley, College of Agricultural and Environmental Sciences, firstname.lastname@example.org
Wine grape growers in California and elsewhere face increasing labor costs and severe labor shortages, making it difficult to manage and harvest a vineyard while maintaining profitability. Growers are increasingly turning to machines for pruning, canopy management and harvesting, but how well these practices are executed can substantially affect yield and quality. A new review by researchers at the University of California, Davis, published in the journal Catalyst, provides guidelines for growers to make the best use of machines.
“Wine grape laborers have been virtually nonexistent. People don't want to work in vineyards anymore because it's remote, tough work,” said Kaan Kurtural, UC Davis professor of viticulture andenology andUC Cooperative Extension specialist. “There is now machinery available to do everything without touching a vineyard.”
Kurtural has designed a “touchless” experimental vineyard at the UC Davis Oakville Station to help growers understand how machines can help them cope with the labor shortage. While machines reduce the need for seasonal manual labor, they do not eliminate it. The degree of labor reduction depends on growing region, grapevine type and the number of practices growers mechanize.
The review provides guidance on using machines for winter pruning, canopy management and harvesting as well as how to design a grape vineyard for machines before planting. Videos showing the operation of different types of machinery and practices can also be found in the review.
Economic savings, quality grapes
About 90% of the wine grapes crushed in the U.S. are mechanically harvested. Previous studies have found about a 50% savings in labor costs from using machines to harvest instead of hand harvesting.
“Using more mechanization in a vineyard beyond just harvesting can also reduce labor costs without affecting grape quality.” Kurtural said.
Mechanical pruning, for example, can save between 60% to 80% of labor operation costs per acre compared to manual pruning alone. One experiment in the San Joaquin Valley, where more than 50% of California's wine grapes are grown, also showed using mechanical canopy management machines to manage merlot grapes resulted in twice the amount of color. The more color, or higher anthocyanin concentrations, the better the quality. It can significantly improve returns from vineyards in California's heartland.
Kurtural said there are machines available to manage canopies, including machines for leaf removal, shoot thinning and trunk suckering. Kurtural noted that the machines are American made, developed by researchers at the University of Arkansas and commercialized by manufacturers in Fresno and Woodland, California.
The review was co-authored by Matthew Fidelibus, UC Cooperative Extension viticulture specialist at UC Davis, based at UC Kearney Agricultural Research and Extension Center. Financial support for the research came from the American Vineyard Foundation and Bronco Wine Company.
A welcome sign of spring each year for grape producers is budbreak, the moment when tiny buds on the vine start to swell and green leaves appear. Budbreak varies by region, variety and even vineyard topography, but in Sonoma County, unseasonably warm weather caused buds to burst early, reported Bill Swindell in the Press-Democrat.
“Perhaps it's the new normal,” said Jen Walsh, the winemaker at La Crema Winery in the Russian River Valley, commenting about long-term change due to global warming.
The Carneros region that borders San Pablo Bay is typically the first wine appellation to experience bud shoots on grapevines, given its milder climate, said Rhonda Smith, UC Cooperative Extension viticulture advisor in Sonoma County. In addition, hillside vineyard areas in the county with south- and west-facing slopes also usually are on the early side because of their longer sun exposure.
There is a downside to early budbreak. The vines are susceptible longer to a potential spring frost, which could harm opening buds and young shoots.
Below are recent tweets heralding the 2020 budbreak around California.
Wine grape growers in the San Joaquin Valley who want to switch from hand pruning to mechanical pruning won't have to replant their vineyards to accommodate machinery, according to a new study published in HortTechnology by University of California Cooperative Extension researchers. Instead, growers can retrain the vines to make the transition, without losing fruit yield or quality.
Mechanical pruning reduced labor costs by 90%, resulted in increased grape yields and had no impact on the grape berry's anthocyanin content. That's welcome news for growers because the cost of re-establishing a vineyard in the region is roughly $15,600 per acre.
“We found that growers do not have to plant a new vineyard to mechanize their operations,” said Kaan Kurtural, UC Cooperative Extension specialist in the UC Davis Department of Viticulture and Enology. “We have proven beyond a doubt that an older vineyard can be converted to mechanization. There is no loss in yield during conversion and post-conversion yield is better and fruit quality is equivalent to or better than hand-managed vines. The economies of scale are evident in the savings per acre and per vine as depicted in the balance sheet provided with the newly published paper.”
The research was conducted in an 8-acre portion of a 53-acre, 20-year-old Merlot vineyard in Madera County. After completion of the research project, the grower converted the rest of the 53-acre vineyard to single high-wire sprawling system. Many other wine grape growers have followed suit.
The Wine Group, which manages 13,000 acres of vineyards across Central California, is establishing new vineyards and converting old vineyards for mechanical pruning and suckering, said vineyard manager Nick Davis. Davis, who works closely with Kurtural and the UCCE viticulture advisor in Fresno County, George Zhuang, said the company greatly values the UC Cooperative Extension research that is guiding the changes.
“I think extensionists are undervalued,” Davis said. “We lean on them for applied research, which has been wonderful. They offer us what we can't provide ourselves.”
More than half of all California wine grapes are grown in the San Joaquin Valley. Worker shortages, rising labor costs, low returns and occasional droughts are driving wine grape growers to seek innovative ways to sustain their businesses.
“To help growers maintain the profitability of their vineyards, we're studying the use of machines to reduce the number of people needed to perform tasks like pruning,” Zhuang said.
“Because the canopy architecture and yield characteristics of mechanically pruned vines are different from vines that are hand-pruned, the water and fertilizer requirements for the mechanically pruned vines can be quite different. So we are studying the yield and fruit quality of grapes produced on different rootstocks in mechanical pruning systems in the San Joaquin Valley,” Zhuang said.
The Madera field study was conducted for three consecutive seasons in the hot climate conditions typical of the San Joaquin Valley. In this area, traditional vineyards are head-trained to a 38-inch-tall trunk above the vineyard floor and two eight-node canes are laid on a catch wire in opposite directions and two eight-node canes are attached to a 66-inch high catch wire. Although this traditional training system can work for mechanical harvesting, it doesn't accommodate mechanical dormant pruning and shoot removal with limited success in other mechanical canopy management operations.
To accommodate mechanical pruning and shoot removal, the vines were converted to a bilateral cordon-trained, spur-pruned California sprawl training system, or to a bilateral cordon-trained, mechanically box-pruned single high-wire sprawling system.
The latter option proved to be the most successful system for mechanical pruning in the San Joaquin Valley.