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August 2015 P R A C T I C A L W I N E R Y & V I N E YA R D 73 W I N E M A K I N G S. cerevisiae can produce the vinyl- phenols through the decarboxylation of cinnamic acids (coumaric or ferulic). Coumaric acid is decarboxylated to form 4-VP and ferulic acid forms 4-VG. This decarboxylase activity of S. cerevisiae is why these vinylphenols are intrinsic to the varietal aroma of Gewürztraminer. This formation of vinylphenols can only happen during alcoholic fermentation and will not continue to occur while the wine is stored on yeast lees. Brettanomyces/Dekkera (Brett) is the microbe that produces volatile phenols of most concern to makers of red wines, 4-ethylphenol and 4-ethylguaiacol. Brett can infect wine at any part of the wine- making process, but it is most notably an issue during barrel aging of wines, as the microorganism can be found up to 8 mm deep in the wood. 15 Brett has the same decarboxylase activity previously mentioned and can synthesize vinylphenols. However, Brett further reduces the vinylphenols by a vinylphenol reductase to form the more odiferous ethylphenols that we associate with this wine fault. Brettanomyces con- taminations are most easily avoided by judicious hygiene, including sulfuring red wines to more than 0.5 ppm of free molecular SO 2 during barrel aging after completion of malolactic fermentation. All methods for barrel cleaning cur- rently available to the winemaker will not sanitize the barrel and cannot com- pletely remove Brettanomyces from the crevices within the wood. However, ozone and steam may delay the onset of infection by killing the yeast on the surface of the wood and significantly reducing some of the population in shal- lower areas of the stave (up to 2 mm). It is for this reason that sensorial monitoring of barreled wine is of utmost importance. If one detects Brettanomyces, one can minimize the impact by removing the wine from the vessel and topping it up with sulfur to a free molecular SO 2 of 0.5 to 0.8 ppm and undertaking sterile filtration of the lot. 4 Dosing the wine with dimethyl dicarbonate prior to bottling if the infected lot is to be blended with uninfected wine will further protect the wine from potential spoilage in bottle. 19 Currently, there are few methods for the winemaker to "clean up" 4-EP and 4-EG in a wine after a Brett infection. The most promising low-cost method is through fining with yeast lees. 5 However, more high tech/high-cost methods have also been developed such as a procedure using reverse osmosis/adsorption, 23 the use of esterified cellulose as a filtra- tion medium 14 and using a molecularly imprinted polymer. 7 Conclusion Wine is commonly referred to as a "com- plex matrix." By breaking wine down into its fundamental components, we can begin to understand how to better man- age our vineyards and wineries to attain the wine styles that our markets desire. Higher alcohols and volatile phenols could be considered a fault or aromas that are intrinsically valuable to our wine style, depending upon what we are try- Compound Sensory threshold in wine (µg/L) 4-vinylphenol . . . . . . . . . . . . . . . . . . . . . . 770 4-vinylguiacol . . . . . . . . . . . . . . . . . . . . . . 440 4-vinylguaiacol + 4-vinylphenol [1:1] . . . . . . . . . . . . . 752 4-ethylphenol . . . . . . . . . . . . . . . . . . . . . . 605 4-ethylguiacol . . . . . . . . . . . . . . . . . . . . . . 110 4-ethylphenol + 4-ethylguiacol [10:1] . . . . . . . . . . 369 S U P P O R T R E S E A R C H & W I N E I N D U S T R Y N E E D S T H R O U G H T H E AMERICAN VINEYARD FOUNDATION AMERICAN VINEYARD FOUNDATION Finding Solutions Through Research P.O. Box 5779, Napa, CA., 94581 • T: (707) 252-6911 • Visit our web site at www.avf.org for information on funding and current research projects For a wealth of useful viticulture and enology research and information, visit AVF.org, ngwi.org, ngr.ucdavis.org, asev.org, or iv.ucdavis.edu For a wealth of useful viticulture and enology research and information, visit AVF.org, ngwi.org, ngr.ucdavis.org, asev.org, or iv.ucdavis.edu Table 1: Sensory threshold of volatile phenols in wine. 18 Economical • EPA Registered for Wine and Table Grapes Short REI • No PHI • Patent Pending Does Not Change the Taste or Character of Your Fine Wines. Proven Effective. Endorsed by Thousands of Growers. Liquid Bird Repellent Call Today For More Information 888-707-4355 Sales@AvianControl.com www.AvianControl.com Drive Birds Away from Barns, Packing Sheds and other structures. Now Approved in California For Vineyards, Wine and Table Grapes