Slowing down the sugar rush to produce better grapes

One of the many challenges that climate change poses to winegrowers is the accelerated rate of ripening of grapes in warmer climates, which can lead to poor color and aroma development.

In a new study published in the Journal of Agricultural and Food Chemistry, researchers at the University of Adelaide found that it was possible to increase the aromatic potential of Cabernet Sauvignon grapes by slowing down the ripening process through strategies such as harvest load manipulation and crop management. irrigation.

“Groups of compounds have responded to different factors including crop load, irrigation, rate of ripening and, in some cases, an interaction of these. Principal Author, Pietro Previtali of the School of Agriculture, Food and Wine, University of Adelaide

Lead author, Pietro Previtali from the School of Agriculture, Food and Wine at the University of Adelaide, said: “Advanced ripening due to warmer temperatures is a key issue for winegrowers in the region. Most wine regions of the world and especially in hot and dry regions like Australia and California. “

“This leads to a faster build-up of sugar in the grapes, which makes it possible to achieve target sugar levels when the concentrations of color and aroma compounds are below their maximum values.

“Wine growers therefore have to make compromises between harvesting when the sugar is ready but the desired flavors are lacking, and prolonging the ripening of the grape until an optimal composition of color, mouthfeel and compounds is obtained. aromatic.

“The problem with extended ripening is that the grapes dry out and yields are reduced with a negative consequence on profitability, and higher sugar levels which lead to high alcohol wines.”

Where previous research has shown that techniques such as thinning vines and intense irrigation at the end of the growing season can alter the composition of wine, the new study examined how these techniques specifically affect the development of aromatic compounds. in the grapes themselves.

Researchers grew Cabernet Sauvignon wine grapes in a commercial vineyard in the San Joaquin Valley of California. The vines were either thinned or irrigated late in the growing season, or both, with grapes harvested throughout the ripening period. These were compared to grapes grown in the same block where no technique was applied.

Researchers found that delaying ripening slows the build-up of sugar, which leads to a decrease in green flavor compounds, undesirable in winemaking, and an increase in fruity aromas, color compounds and mouth feel, associated with wine. quality of red wine.

They also observed that the composition of grape quality traits does not depend on a single strategy.

“Rather, groups of compounds were sensitive to different factors including crop load, irrigation, rate of ripening, and in some cases an interaction of these,” said Previtali.

Using the strategies available, the researchers sought to obtain the longest possible time frame to study the relationship between sugar accumulation and flavor development. For example, a three-week delay was achieved through a 35 percent reduction in harvesting load and end-of-season irrigation of 50 percent additional water.

“Although it represents a valuable experimental tool, however, this approach may not be practical due to the availability and high cost of irrigation, especially as water becomes a more scarce resource,” said the project leader and co-author, Associate Professor Christopher Ford, University of Adelaide. .

“Adapting the management of these strategies seems to be the way to achieve the targeted levels of aromatics, color and mouthfeel in wines. “

The researchers say that replication of these wine trials in future seasons is necessary to fully understand the implications of year-to-year variations and to develop a broader understanding of the combination of harvest load and crop load. end-of-season irrigation to delay sugar build-up.

The study was conducted within the ARC Training Center for Innovative Wine Production based at the University of Adelaide, with research partners from the Training Center and E. & J. Gallo Winery in California.

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