"True Facts" Filtered Controversy

Wanna start a fight with a winemaker? Just take a side on the filtering issue and you are guaranteed a feisty discussion. Magazine writers and wine reviewers fawn when they see “unfined, unfiltered” on a label, so it follows that consumers just accept a view that a filtered wine is therefore something less, having had aspects of a its aroma and palate filtered out. The best filtration is no filtration! But is that entirely true?



Filtration is a common practice in winemaking even if not everyone agrees on its necessity to create great wine. Some winemakers brag that their wines are unfiltered and therefore better. The argument goes that filtration can rob wine of desired qualities, such as taste and smell, leaving a wine that is clear to look at yet without character, and further justified with the mantra that wine should be manipulated as little as possible. Those braggarts tell us to believe that an unfiltered wine has more intense flavors, texture and aroma.

Let’s agree that when possible, wine should not be filtered.  The less a wine is needlessly tampered with, the better. Filtration by definition removes something; some character from a wine.  Some of this character invariably contributes to the texture and aromatics of a wine. Filtering also adds an additional step to the bottling process and increases the risk of oxidation as the wine goes from filtration to bottle.

Why Filter Then?

Filtration involves removing sediment, grape skins, dead yeast and other particles from wine by passing it through filter media that has (microscopic) holes big enough for the wine to pass through yet small enough to catch any floating particles. Judicious filtration removes yeast, microbes and other larger solids while still allowing the tiny molecules that are responsible for color, flavor and aroma to pass through the filters, allowing clarity and brilliance to be achieved. Using a filter properly does nothing but remove undesirable microorganisms and solids and should not have any major effect on flavor and aroma.

The experienced and pragmatic winemaker knows that there are serious risks involved in bottling a wine with an unknown load of bacteria and, perhaps, yeast. there are a significant number of wines on the shelves in retail stores with the telltale signs of post-bottling microbial growth. Filtering largely removes that risk and, therefore, it is often standard procedure.

Filtration makes a wine “brighter,” meaning clearer, and attractive to look through in the glass. Myself and most of the wine drinking community expect a wine to pour clear, not cloudy and opaque.  A winery may decide to filter for strictly this cosmetic reason.  But as previously said, a winery may decide not to filter their wines because they feel that too much of the wine is left on the filter media, and that the unfiltered wines taste better and have superior mouthfeel. 

To filter or not to filter involves compromises on both sides of the question. What I find from talking with many winemakers is that the filtration question becomes a philosophical, even emotional one rather than a practical one based on logic.
 
One could make a convincing argument that carefully made fine red wine that has been matured in barrel shouldn’t even need filtering.  Racked off after spending months in wood a wine should be stable against problems caused by protein and tartrates, as well as yeast and bacteria problems. By the time the winemaker has coarse filtered and fine filtered, the wine is already brilliant.


As a practical matter, in some cases filtering is an absolute necessity. Such as the case for any wines containing residual sugar. It could be entirely necessary for wines containing malic acid - to prevent malolactic fermentation in bottle. Similarly, wines intended for short-term consumption often don't have the acidity, or alcohol and tannin levels that offer resistance to biological instability. Wines made for ageability and to be cellared might be expected to have a little sediment after some years, but most consumers have little understanding or tolerance for the appearance of natural crystals and deposits in an early-drinking wine. 

This means that pretty much all white wines should probably be filtered to a sterile degree. For a red wine where absolutely no Brettanomyces influence is to be acceptable, then a winery really has to weigh filtration’s slight effect on mouthfeel against the chance that the wine will smell like a barnyard in a year or two. 


Winemakers and consumer should be cautious of building a philosophical argument on a practical issue like filtration. If you want the benefits of labeling your wine as unfiltered, you had better take the trouble to ensure that the wine you bottle contains no more than a minute quantity of viable cells, and that your customers won’t be put off by an opaque appearance or sediment. A balance of a low level of bacteria combined with a relatively high level of sulfur dioxide would be the aim for a wine that is not going to be filtered. 




What's Involved

Wineries use filtration systems with a series of different grades of pads (or cartridges). The process begins with the wine being filtered through coarse filter pads, then may continue undergoing a second "fine" filtration, using clarifying filter pads, followed by a third "polish" filtration, which can result in the wine taking on a brilliant clarity. A final step, "sterile" filtration, uses membrane filters that are fine enough to remove yeast cells, thus preventing further fermentation.

The sterile filters commonly used nowadays are usually a tight depth filter depth and then a membrane filter.

Sources: www.winebusiness.com, and Gary Baldwin - Australian wine consultant