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w w w. v w m m e d i a . c o m N o v - D e c 2 014 | V I N E YA R D & W I N E RY M A N A G E M E N T 3 9 STERILE FILTRATION TO THE RESCUE Despite a winemaker's best efforts at sanitation, microbial con- tamination may occur in a wine that has chemistry that renders the wine vulnerable to microbial spoilage in the bottle. Some types of wine that intentionally have residual sugar or malic acid can be at risk. Sterile fil- tration is often recommended when the conditions indicate there is a risk for microbial growth and spoil- age of the wine post-bottling. Sterile filtration will remove the microbes, but also colloidal par- ticles. Perhaps it is the removal of these colloidal particles that people are concerned about when they think of losing a wine's character in the filtration process. Most indi- vidual wine flavor molecules will fit through a sterile filtration media, but larger, aggregated particles may be removed. In some cases, the removal of col- loidal particles may be a good thing in that it can improve a wine's clarity. Turbidity results from the presence of microorganisms and/or colloidal aggregates in the wine. Filtration that reduces the amount of microbes and colloidal particles will result in decreased turbidity. In general, as the pore size gets smaller, i.e., tight- er filtration, there is a decrease in the turbidity of the filtered wine. It is understandable that many winemakers shy away from filtra- tion. It's an extra step in the pro- cess and also results in a small loss of wine. It is another manipulation of the wine and an opportunity for it to pick up dissolved oxygen if not done with the utmost care. While many trials have shown, and many winemakers believe, that there is minimal or no negative impact on the sensory perception of a fil- tered wine, others believe there is a difference. But having an unfiltered wine spoil in the bottle must be avoid- ed. If the chemistry and microbiol- ogy indicate there is a likelihood of microbial activity post-bottling, it is probably a good idea to sterile-filter the wine. There are many different options and equipment to use for fil- tration, and modern technology has reduced, or nearly eliminated, any obvious sensory impact to the wine. Remi Cohen is the vice president of operations for Cliff Lede Vine- yards in Napa Valley. Her primary areas of expertise include viticulture, sustainable vineyard management, winemaking, grower and winery relations, and strategic business development. She also writes a wine industry blog, which can be found at blog.vinestowine.com. Comments? Please e-mail us at feedback@vwmmedia.com. SOIL & CELLAR REMI COHEN