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Charles G. Edwards Inquiring Winemaker Can Brettanomyces Be Managed? B. Petrova, School of Food Science, Washington State University Editor's note: Tim Patterson is on temporary leave from writing the Inquiring Winemaker column while he works on his next book. Winemaking researchers, teachers and professional winemakers will be contributing to this page during his absence. M any people in the wine industry consider Brettanomyces to be a significant threat to red wine quality. During red wine aging (maturation), infected wines develop a number of off-odors and flavors, which range from clove, spicy, smoky, leather and cedar to more intense (and negative) descriptors as medicinal, Band–Aid, mousy, wet wool, barnyard or—in extreme situations—sewage. Although actual economic losses are not known, it is clear that the yeast remains a major headache for winemakers. This article provides background regarding Brettanomyces as well as approaches for managing infections. What is Brett, and what does it do? The yeast genus Brettanomyces (Dekkera is the spore-forming equivalent genus) was first isolated from wines in France, Italy and South Africa around the same time (late 1950s). While researchers from South Africa initially described the occurrence of B. intermedius and B. schanderlii, other species names have also been published including B. lambicus and B. vini. Today, the most dominant species found in wines is thought to be B. bruxellensis (see photo at right). One of the keys to understanding Brettanomyces is that the yeast is capable of forming the "volatile phenols" 4-ethyl phenol (4-EP), 4-ethyl guaiacol (4-EG) and 4-ethyl catechol (4-EC). While Highlights • rettanomyces can be spread from barrel to barrel and winery B to winery through poor sanitation of equipment (pumps, hoses, wine thieves, etc.), used barrels, importation of contaminated wines or other means. • y applying a variety of detection methods, early discovery can B help limit the spread of infections even in small wineries. • he yeast can be effectively managed using "hurdle technolT ogy," where as many strategies as logistically and financially possible are employed. 78 W in es & V i ne s APR I L 2 013 Electron microscopy shows Brettanomyces isolated from Merlot. 4-EP is described as having "Band-Aid" or "plastic" odors, 4-EG smells more "medicinal" or "spicy." 4-EC has been reported to have "spicy," "woody," "smoky" or "horsey" odors, although its impact on wine quality remains unclear given the tenfold variation in reported sensory thresholds. All three volatile phenols originate from hydroxycinnamic acids naturally present in grapes; 4-EP from p-coumaric acid, 4-EG from ferulic acid and 4-EC from caffeic acid, as illustrated in the diagram on page 80. Besides Brettanomyces, some lactic acid bacteria (most notably Lactobacillus plantarum and yeasts like Pichia guilliermondii) can also produce ethyl phenols—but generally in smaller concentrations, if at all. In addition to volatile phenols, Brettanomyces can synthesize a wide range of other compounds that smell "rancid" (isovaleric acid), "mousey" and other descriptors. Thus, the sensory impact Brettanomyces has on wines is not as straightforward as volatile phenol synthesis. How do I know if I have Brettanomyces in my wine? While most winemakers regularly smell/taste barrels, some do not, thereby missing opportunities for detection of problems. However, solely relying on smelling barrels for Brettanomyces may be too late, as very low populations can cause spoilage. To approach limiting these infections, a wide-ranging, rigorous monitoring program is needed. Firstly, any suspected wines should be isolated from the cellar. Above all, the winemaker needs to avoid spreading the yeast to other barrels or tanks through inadvertent sampling with a nonsterile wine thief or equipment.