July 2007 Issue of Wines & Vines
 
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When to Filter

Know your wine first, winemakers say

 
by Tim Patterson
 
 
    HIGHLIGHTS
     

     
  • While filtration has been a mainstay of commercial wine production for decades, the range of available technologies has increased and improved, and winemakers have gotten smarter about how to maximize the usefulness of filtration and minimize the potential side effects.
     
  • Crossflow membrane filtration has been in use in the food industry since the 1960s; early attempts to apply it to winemaking were problematic, and only in the last two or three years have improvements in the equipment made it a hot item.
     
  • For white wines, filtration is clearly the norm, and sterile filtration is quite common. Decisions are tougher to make with red wines, which provide more opportunity for microbial mischief, but are better than most whites at absorbing small amounts of off flavors and aromas.
Filtration is one of those aspects of wine production that is often practiced and rarely talked about. The filter folks always get plenty of traffic at the wine trade shows, but it's hard to imagine a winery boasting about its new sterile membrane setup in its wine club newsletter.

People who expect their water, their coffee, their cigarettes and their e-mail to be filtered somehow get nervous when it's wine getting the treatment. Was there something really nasty in that wine they had to take out? Or, even worse, was there something really yummy in there that got yanked in the process? Most likely, a winemaker was taking prudent, sensible steps to put sound wine in the bottle and avoid unwanted microbial adventures.

The vast majority of wine in the marketplace, even at the very high end, goes through one kind of filtration experience or another, in order to achieve some combination of clarity and microbial stability. That generalization was confirmed anew when half the winemakers I contacted for this story had to call me back later, after they had finished…a filtration. While filtration has been a mainstay of commercial wine production for decades, the range of available technologies has increased and improved, and winemakers have gotten smarter about how to maximize the usefulness of filtration and minimize the potential side effects.

The Crossflow Grail
Pall OenoFlow
This Pall OenoFlow crossflow filtration unit is similar to one on loan to the winery at California State University, Fresno.
Photo: Courtesy of Pall Corp.


Crossflow membrane filtration continues to be the buzz-worthy topic in discussions of technological alternatives. The basic distinction between crossflow and other filtration methods is the direction of flow. Standard membrane filters and plate-and-frame (pad) filters send the wine straight into the filter medium, a perpendicular flow that traps the solids (called the retentate) inside or against the filter medium, while crossflow pushes the wine across a porous membrane, with the wine passing through the pores and the solids continually washed away by the incoming wine. The core technology has been in use in the food industry since the 1960s; early attempts to apply it to winemaking were problematic, and only in the last two or three years have improvements in the equipment made it a hot item.

From his perch at CSU Fresno, professor Ken Fugelsang sees a lot of interest in crossflow across the country, in large and medium-sized wineries and increasingly in smaller operations as well. Among the advantages he cites are that the membrane can be used for a long time, with no expendables (pads or diatomaceous earth) to dispose of. Since the solids are washed away, crossflow systems can handle relatively "dirty" wine without building up a cake and requiring backwashing-the membrane cartridge is more or less self-cleaning. Crossflow systems are also efficient. "It's not unreasonable to expect the retentate to be only 1 gallon out of 1,500," Fugelsang estimates. Plus, automation in some models makes it possible to plug in some hoses, turn it on, and go off and do something else.

The downside starts with the cost-$25,000 to $50,000 and up-depending on capacity and the degree of automation. (Fugelsang's CSU Fresno winery is lucky enough to have one on loan from the Pall Corporation.) And although most crossflow membranes are rated at .2 micron - theoretically tight enough for sterile filtration - it's only a nominal rating-a best guess, not a guaranteed filtration level. Unlike absolute sterile membrane systems, crossflow membranes can't be pressure-tested for integrity before use, which means that a winery that demands dependable sterile filtration still needs that additional equipment.
Doug McCrea
Owner/winemaker Doug McCrea, McCrea Cellars, is among many smaller producers who has chosen not to invest in pricey crossflow filter systems, though some use mobile services for some wines.


There are also a lot of winemakers who would agree with Doug McCrea of Washington's McCrea Cellars that, "If it ain't broke, don't fix it"-an expression of satisfaction with his current equipment and procedures. For the moment, purchases of crossflow systems by small wineries are limited to early adopters-though quite a few use mobile crossflow capacity for certain wines, and many winemakers have an eventual crossflow purchase on their wish lists.

Filtering Whites

Since all the flavors of filtration technology can do the job, once people in the cellar get the hang of the quirks of any chosen method, the more interesting question is when to filter, and to what end? There is a school of thought, particularly within the ranks of small, high-end wineries, that says the right time to filter is never-that such forceful intervention goes against the grain of natural winemaking and strips out irreplaceable flavor and mouthfeel components. The debate over filtration remains mainly anecdotal, with hard evidence on the question of stripping still scarce. For the great majority of winemakers, the issue is not so cut and dried, not so philosophical, but much more practical.

For white wines, filtration is clearly the norm, and sterile filtration is quite common, nearly universally among those who produce wines with residual sugar or without malolactic fermentation. In the Finger Lakes of upstate New York, David Whiting of Red Newt Cellars follows a standard routine with his whites-dry, off-dry, with or (usually) without malolactic, vinifera and hybrid varieties alike. Wines are allowed to settle and clarify until February or March; filtered at 1 or 2 micron with a 24-plate Seitz plate and frame filter. At bottling time, a final tight pad filtration is followed by an absolute .45 micron sterile filtration with an Aftek cartridge membrane filter.

Across the country in Washington state, McCrea used to make an unfiltered Chardonnay, which met with some consumer resistance because of less than perfect clarity. Now that his white lineup is all Rhône varieties, most of which don't go through malolactic, filtration is standard. He's been using the same SEM plate and frame for a dozen years; he normally starts with a 1 micron pad, then a half micron, finishing up with a sterile Seitz cartridge in the bottling line.
Alternative text
At Mount Eden Vineyards in California's Santa Cruz Mountains, Jeffrey Patterson uses very little filtration.


Jeffrey Patterson at Mount Eden Vineyards in the Santa Cruz Mountains is at the low-filtration end of the white spectrum. All his whites (mostly Chardonnays) are aged on their gross lees, fermented entirely dry and put through a full malolactic. Filtration is therefore done simply for clarity and polish. In most cases, a single 1.2 micron pass through a Seitz plate and frame with a Waukesha pump is sufficient. If the wine is unusually hazy, Patterson uses a diatomaceous earth (DE) system with a dosage regulation unit from Process Engineers; with his small case output, disposal of the DE is not a significant issue.

Filtering Reds

Decisions get tougher to make with red wines. On the one hand, the generally higher pH values and longer aging times before bottling provide more opportunity for microbial mischief, in the form of Brettanomyces, Pediococcus and other lactic acid bacterial spoilage, and so on. On the other hand, hearty red wines are better than most whites at absorbing small amounts of off flavors and aromas, and higher-end reds especially are prized for delivering lots of body, extract and mouthfeel-stuffing nobody wants to lose.

Most winemakers straddle this dilemma by trying to filter no more than necessary-but always filtering when it is necessary. That standard naturally leaves a lot of room for judgment in between-and means that winemakers really have to know what's up with their wines to make intelligent decisions.
B. Kiley Evans
Production is small at Abacela Vineyards, so winemaker B. Kiley Evans filters only when necessary to avoid losing wine.


B. Kiley Evans, winemaker for Abacela Vineyards in Oregon's Umpqua Valley, sterile filters his white wines, since none of them go through malolactic, but he hesitates to filter the reds-Tempranillo, Dolcetto, Syrah, Grenache, Malbec-because Abacela is a small-batch winery, and filtration means wine loss. He had just finished bottling a Malbec, and the filtration had taken six cases out of a 225-case lot.

He uses filtration when it will improve a wine or make it sounder during aging. In the case of Malbec, for example, he thinks that a rough filtration brightens the fruit character. On the other hand, reds with significant Brettanomyces activity may get sterile filtered. Abacela's current equipment includes a Della Toffola plate and frame filter and a Pall cartridge membrane; "Crossflow," he says, "is in our future."

Doug McCrea worries about the presence of residual sugar in his wines, just that much more fuel for unhelpful bacteria. He notes that grapes are getting picked at steadily higher Brix levels, and swears that somehow Washington grapes convert the same amount of sugar to slightly higher alcohol. In any case, when he detects any trace of residual sugar, anything over .2%, he will at least do a 1 micron pad filtration and a 1 micron cartridge before bottling. If there is also evidence of bacterial populations, sterile filtration may be required. He observes that the winery just got some high scores for certain sterile-filtered 2004 reds.
Della Toffola DE
This Pall OenoFlow crossflow filtration unit is similar to one on loan to the winery at California State University, Fresno.
Photo: Courtesy of Pall Corp.


David Whiting's Red Newt reds are bottled just before the next harvest, and undergo one filtration during aging. "On bottling day," he says, "depending on the wine and its microbial history, it may go through a 1 micron pad or through a sterile filtration just like the whites." Like other winemakers, he tries to keep the filtration lightest on his highest-end wines.

When I called Ken Volk, longtime winemaker for Wild Horse on the Central Coast and now running his own Kenneth Volk label, he was in the middle of filtering Cabernet and Merlot. "I'm a big believer in filtration," he says. "More great wines are filtered than not." For these particular wines, with no residual sugar, no incomplete malolactic and no volatile acidity, he decided that a .6 micron pad followed by a .65 micron nominal on the bottling line should capture most of the bacterial load. For many jobs, he uses a crossover plate and frame system that allows wine to go through two different levels of pad filtration in a single pass.

Volk emphasizes that the same technology in different hands can have different results. He stressed the importance, for example, of properly preparing pads with acidulated water and then pushing out the water before running an actual filtration; the need to acidulate with DE filtration media as well; the importance of filtering as closely before bottling as possible, since a tank of wine can go through a lot of changes in a couple days; and the value of a pressure sensor to regulate the flow from the pump in a filtration system.

Volk is among the winemakers who utilize mobile/contract services for crossflow filtration. He likes crossflow for his Pinot Noirs, having observed that crossflow is less likely to knock down aromatics than other methods; he hasn't been especially happy with crossflow experiments on Bordeaux varieties.
Elias Fernandez
Winemaker Elias Fernandez uses a diatomaceous earth filter system at Napa's Shafer Vineyards.


Diatomaceous earth filtration has taken some hits to its image in recent years; critics point to relatively higher wine loss, disposal issues, and health and safety concerns for operating personnel. But Elias Fernandez, winemaker at Shafer Vineyards in Napa and a mainstay of the cellar there for more than 20 years, thinks their Della Toffola DE system does just the job they need done. With years of experience and a safety program in place, he finds that DE has more wine throughput and provides the clarification-not sterile filtration-that suits the Shafer style. Fernandez is another winemaker who hasn't been convinced about the virtues of crossflow, based on experiences a few years back.

Jeffrey Patterson, the filtration minimalist in my survey, has a goal of not filtering his reds (Cabernet and Pinot Noir). He makes sure the wines are completely dry and have gone entirely through malolactic. The only remaining question is the presence of spoilage microbes, particularly evidence of Brettanomyces in the form of 4-ethyl phenol (4EP), 4-ethyl guaiacol (4EG). "Generally," he says, "we don't have that problem. I also don't worry about a tiny bit of haze in a red wine; whites demand more aesthetics." His reluctance to filter reds is based on the possibility of damaging mouthfeel and suppressing aromatics.

The take-home from this random survey of smart winemakers in four states is not so much about the pros and cons of any particular piece of equipment; it's the importance of knowing everything about the wine in that tank-not assuming anything, neither the best nor the worst.

Resources: Filtration Suppliers

(Tim Patterson writes for a cuvée of publications about adult beverages-and makes his own-in Berkeley, Calif., where the wine country meets what's left of the '60s. He may be contacted through edit@winesandvines.com.)
 
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