RICHLAND, Wash. - Winemakers can practice more stylistic control over their product than previously thought, according to new research from Washington State University's Department of Viticulture and Enology (V&E). The increased predictability is advantageous as the planet's warming climate causes grapes to ripen faster.
The study, published in the journal Food Chemistry, analyzed data on Sauvignon blanc grapes over a two-year period to determine how pre- and post-fermentation alcohol adjustments influenced the sensory and aroma profiles of wines made from fruit at varying stages of ripeness. The researchers concluded that pre- and post-fermentation alcohol adjustments result in comparable impacts.
"Winemakers can mitigate some of climate change's effects by diluting when they bring in the fruit, or de-alcoholizing later," said Jim Harbertson, study co-author and associate professor in WSU's V&E department. "They can still create the style of wine they were trying to make, even if the weather got too warm too quickly."
Because a grape's composition changes as it ripens, winemakers typically time harvests based on how they want their wines to taste and smell. Riper grapes mean more sugar, and more sugar results in more alcohol.
"Our research demonstrates that winemakers don't have to make all of their flavor decisions in the vineyard," said Danielle Fox, study co-author and recent PhD graduate from WSU's School of Food Science. "There's a lot of flexibility around harvest time and many tools in the winery that can be used to adjust the wine and enhance the desired flavor profile post-fermentation."
Winemakers can control the alcohol concentration of their wines pre-fermentation by using water dilution or chaptalization, a process that involves adding sugar to grape juice. They can also adjust alcohol concentration post-fermentation via a method called de-alcoholization. Aromas in a glass of wine largely depend on the amount of alcohol - the higher the alcohol concentration, the more aroma compounds.
In light of recent warnings from government agencies about the health risks associated with alcohol consumption, many winemakers are using de-alcoholization to respond to growing consumer demand for low- or no-alcohol beverages.
"Alcohol removal is clearly a huge movement in the wine industry right now," Harbertson said.
However, removing alcohol can have negative results, including an increased perception of sourness.
"Alcohol adjustment strongly dictates the majority of the sensory attributes of wine, including aroma, bitterness, heat, and mouthfeel," Harbertson said. "Alcohol is what defines the wine. Removing it emphasizes the negative sensory aspects. It's tricky, and it may mean that we need to rethink what we're trying to create."
While previous white wine grape research has focused heavily on Chardonnay and Riesling, this study helped the researchers understand Sauvignon blanc's unique characteristics. Known for its tropical, fruity, and grassy aromas, the cultivar is commonly grown in Washington state vineyards. Unlike many other varieties of grape, Sauvignon blanc aroma compounds change significantly from one grape harvest to the next.
Alcohol adjustment strongly dictates the majority of the sensory attributes of wine, including aroma, bitterness, heat, and mouthfeel.
Jim Harbertson, associate professor
WSU's V&E department
"We concluded that Sauvignon blanc grapes lose their unique varietal character and aroma compounds after a certain harvest point," Fox said. "If winemakers harvest the grapes when those aroma compounds are present, then adjust that juice or wine so it has a higher alcohol level, it can actually enhance the wine's aroma."
Using fruit from three different grape harvests, the researchers set out to determine what differences in the wines were caused by ripening, and which were a result of alcohol concentration. To do so, they asked a panel of testers to describe the aroma and taste attributes they detected. The researchers were surprised when the panelists distinguished between the wines' aroma and taste attributes based on alcohol concentration, rather than ripeness.
"We found that the alcohol largely dictates a wine's aroma," Harbertson said. "It's essentially a winemaker's technical treatise on making different styles of wine from the same harvest. Because Sauvignon blanc changes as it ripens, winemakers tend to pick it at different times, then combine the wines they make later. We've proved that you can essentially make the wine taste 'unripe.'"
Much of the previous sensory research on alcohol adjustments has focused on changing grape juice before it's fermented. This study expanded upon that, showing winemakers they have options.
"It was important for us to push the boundaries and take the research further," Fox said. "Sensory analysis is expensive and time-consuming. Our findings will allow us to make predictions about a wine's aroma and maximize efficiency going forward."
