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Inquiring Winemaker TIM P A T TERSON The Great Filtration Debate, Continued issue), the debate was at a standoff. Le- gions of artisan winemakers swore up and down that they knew from personal experience that filtration ripped the heart and soul and guts and wonderfulness out of wine. The science crowd, on the other hand, said they doubted this could be the case, since every known molecule of aro- matic, flavor or textural significance was far too small to get trapped in even the tightest filter. Plus, filtration helps with clarity and microbial stability. I compared the poor, confused enologi- T cal community to Hamlet, winemaker for Prince of Denmark Vineyards, forever go- ing back and forth: T o filter, or not to filter—that is the question: W hether 'tis nobler in the mind (of the winemaker) to suffer T he slings and arrows of outrageous particulates O r to take arms against a sea of microbes And by removal end them. That's where the issue stood for a good long time: One side advancing subjective, personal testimonials, the other side offer- ing a purely theoretical refutation, with neither team having much in the way of hard evidence. Well Hamlet, maybe now you can re- lax a bit, because some data is finally in the house. David Block and his lab at the University of California, Davis, have been offering sneak previews of the findings of 92 WINES & VINES NOVEMBER 2012 he last time I devoted this col- umn to the ongoing discussion about the merits of filtration (see "If Filtration 'Strips' Wine, What's Getting Stripped?" in Wines & Vines' October 2008 If filtration removes something positive and important from wine, it's now up to the anti-filtrationistas to show what that something is. an extensive, carefully controlled series of experiments combining chemical and sen- sory analysis, and the results suggest—to oversimplify just a bit—that properly done sterile filtration does not seem to remove anything detectable in wine that you'd re- ally want left in there. The Davis work won't end the debate, of course, and one study is only one study. But for folks who have always wanted to inject some facts into the argument, this effort definitely raises the bar. If filtration removes something positive and important from wine, it's now up to the anti-filtra- tionistas to show what that something is, how to measure it, how winemakers can control it and whether ordinary mortals can taste it. Filtration scenarios The work coming out of Davis involved several grad student researchers in the Block lab, with Luke Bohanan in the lead, combined with sensory analysis done in Hildegarde Heyman's lab, and Roger Boul- ton and other folks chipping in their two cents' worth along the way. As I scribble this, the results are not yet formally writ- ten up or submitted for refereed publica- tion, but the highlights have been offered in a number of semi-public settings includ- ing extension sessions at Davis and this year's ASEV meeting in Portland. The team looked at three wines—a 2007 Sonoma Valley Cabernet Sauvignon, a 2009 Oakville Merlot and a dry white blend (Chardonnay/Muscat)—and gave all of them a variety of treatments. The Cabernet, post-malolactic fermentation and after some barrel aging, was broken down into an unfiltered control, three rep- lications of sterile (0.45 micron) filtration using a PVDF membrane, three replicates using a PES membrane and three replicates using no cartridge at all, just passing the wine through the filter housing in case transport rather than filtration might have made a difference. To eliminate another variable, all the fil- tered wines were pushed with nitrogen gas rather than being pumped, and all were filtered in-line immediately on the way to bottling. Color and tannin chemistry were measured right before and right after fil- tration, and descriptive sensory analysis by trained panels was conducted right after bottling and at three, five, seven and nine weeks out, zeroing in on a couple dozen specific aroma/flavor characteristics. I'll spare you all the tables, significance calculations and spider plots, engaging as Highlights • Research coming out of UC Davis adds to the longstanding debate about wheth- er filtration robs wine of its character. • Previews of the Davis work suggest that in comparisons of filtered and unfiltered wines, no significant chemical or sen- sory differences were identified. • Not everyone is convinced, and one area for further research is the role of colloids, which may be disrupted by filtration.