Alcohol Levels Play a Role in Wine Appreciation

ASEV conference covers wide range of wine research

by Andrew Adams
asev roger boulton
Dr. Roger Boulton of the University of California, Davis, was honored with the ASEV Merit Award in recognition of more than 30 years of extensive research in viticulture and winemaking.
Portland, Ore.—Drinking wines with high alcohol levels can influence the perception of other wines, especially those with lower levels of alcohol, according to findings of a study presented this week during the national conference of the American Society for Enology and Viticulture (ASEV).

Speaking at the ASEV meeting in Portland, Ellena S. King reported the findings of a project she conducted with Randy Dunn and Hildegarde Heymann of the University of California, Davis, indicating that when a panel of tasters evaluated wines grouped from the lowest levels of alcohol to the highest, the tasters found the higher alcohol wines to be far more flavorful and interesting than the preceding wines with low-alcohol levels. “There was a significant enhancement in the sensory attributes of the wines,” King said.

Conversely, when the higher alcohol wines preceded those with lower levels, the tasters found those low alcohol wines to have diminished flavor attributes and enhanced vegetative qualities.

King’s aim was to assess how alcohol in Cabernet Sauvignon can affect sensory properties because of the significant increase in alcohol levels during the past two decades. She noted that alcohol has been on the rise in California, France and Australia for a variety of reasons from clone selection, hang time and changing wine styles.

For the study, King used 24 U.S. wines selected to represent a range of styles and 12%-16% alcohol levels, which were confirmed using an Anton-Paar alcolyzer. King noted that wines with labeled values of more than 14% alcohol tended to undervalue the amount of alcohol, but no wine was found to have an alcohol level outside of legal variation.

The wines were grouped into those lower than 14% alcohol and higher. Eight wines came in lower and 16 were found to be higher. Three panels of 11 to 12 trained testers evaluated the wines in groups tasting in a random order, higher alcohol first and lower alcohol first. 

“The results indicate that initial assessment of high-alcohol wines can reduce perception of aroma and taste descriptors, while the opposite is true when low-alcohol wines are assessed first,” King wrote in her abstract on the study. “This suggests the need to consider wine alcohol concentrations when professionally assessing wine quality, such as at wine shows.”

An alternative to bentonite
A crowd of more than 200 attended the keynote seminars in enology presented by Dr. Liz Waters with the Grape and Wine Research and Development Corp. and Dr. Roger B. Boulton with UC Davis.

Waters described her work studying a possible alternative to bentonite, used throughout the wine industry for clarifying wines for heat stability.

Haze develops from proteins that are found in grapes and released during the winemaking process. Over time, or if the wine is exposed to warm temperatures, the proteins can denature and then coalesce into larger compounds. “If these particles get big enough for us to see them—that’s about one micron—the wine will begin to haze,” she said.

Bentonite is added to wine most often as slurry and will absorb those proteins and settle out on the bottom of the tank. Interest has been growing to find an alternative method of treatment to reduce the amount of used bentonite heading to landfills and from the loss of product in the heavy lees created by fining.

One possible alternative Waters has studied is the food-grade proteolytic enzyme aspergillopepsin, which can block the haze-forming proteins from linking and is active at wine pH. Waters dosed 1,000 liters of Sauvignon Blanc with a high level of protein at a rate of 15 mg/liter and used a heat exchanger to raise the temperature to 75°C for one minute before rapidly cooling to 3°C.

Compared to untreated controls and bentonite treatment, the wine exhibited no hazing. “That’s pretty good; you go from a very hazy wine to one that’s commercially bright,” Waters said of the trial that she successfully repeated six times. “Every time this has been done it’s been successful.” 

Boulton provided an overview about the cold stability options for wines including fluidized-bed crystallizers, electro-dialysis and adding substances to prevent the formation of tartrate crystals.

Earlier in the day, Boulton received the ASEV Merit Award for contributing “in an outstanding manner to the progress and advancement of enology and viticulture.”

Boulton has been with UC Davis since 1976, compiling a lengthy record of research across a variety of subject in winemaking and grapegrowing as well as collaborating with fellow Davis faculty members Linda Bisson, Vernon Singleton and Ralph Kunkee to write the textbook “Principles and Practices of Winemaking.” The text earned the OIV Prix en Oenology in 1998. Boulton has held the Steven Sinclair Scott Endowed Chair professorship since 2000.

In addition to his remarks about cold stability, Boulton presented an overview of his work developing a mathematical model of the oxidation reactions in wine. Boulton developed the model to estimate the yield of acetaldehyde and predict the effect of pH on oxidation reactions.

Far-ranging scope of research
The conference was the 63rd by the ASEV and began Monday with a technical tour of a few Willamette Valley wineries. On Tuesday a panel of experts discussed alternative varieties and their possible use in the U.S. wine industry.

On Wednesday and Thursday, conference attendees had their pick of 60 sessions covering a breadth of research in winemaking and viticulture as well as four detailed industry seminars about specific issues ranging from dealing with botrytis and laccase in the cellar to precision viticulture. The conference also featured posters describing the work of 84 projects by researchers throughout North America as well as France, Uruguay, Australia, Germany New Zealand and Italy.

Best paper honors went to the Australian team of Frank Schmid, Paul Grbin, Andrew Yap and Vladimir Jiranek for their study of the relative efficacy of high-pressure hot water and high-power ultrasonics for wine oak barrel sanitization.

Craig Austin, Gary Grove, James Meyers and Wayne Wilcox from Cornell and Washington State universities authored the winning viticulture paper that explored powdery mildew severity as a function of canopy density.

The conference concluded today with several sessions exploring the work of Kunkee, who studied yeast and wine microbiology at UC Davis and passed away earlier this year.

Audio and video recordings of the conference proceedings will be available at the ASEV website. Next year’s conference will take place June 24-28 in Monterey, Calif., and the 2014 conference is scheduled for June 23-27 in Austin Texas.

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