For quite some time, the debate over whether or not to filter a wine has intrigued wine professionals and consumers alike. Unfiltered wines are often marketed as superior. I don't think I have ever seen a wine marketing campaign discussing anything about a filtration program except for the absence of one. So what's the point, who's doing it, and does it help or hurt?
It just sounds right. It makes sense that marketers have absorbed this into the increasingly popular 'minimalist winemaking' campaigns. Unfortunately, this gives consumers the impression that filtered wines must have had a problem to warrant such intervention.
Perceived benefits of unfiltered wine go beyond the the marketing aspect. Proponents will argue filtration decreases complexity as it inherently removes positive aspects of wine, stripping components that aid in maturation and increase aromas and flavors.
Filtration is the process of removing particulate matter by passing wine under pressure through a filter medium.
Clarification is the most obvious reason for filtration. Time is arguably the best clarification technique because many wines can be sufficiently clear of haze and sediment if given enough maturation time prior to bottling. However, variables such as demand and wine style call for many wines to be bottled relatively young. I have worked with wineries who bottle wines just six months after harvest. The use of fining agents can increase the amount of time required for settling, or make filtration necessary.
Filtration is largely about managing risk. Microbial stability of wine is a constant concern for winemakers, who painstakingly nurture wines right up until bottling to ensure they are in optimum condition. Once in bottle, the winemaker is powerless. Filtration is the best way of removing undesired microbes, such as brettanomyces, that pose threats to wine quality. It is also the best way to ensure microbes necessary during certain stages of the winemaking process are removed. Wines bottled with residual sugar are susceptible to further fermentation in bottle if yeast is present, just as wines that do not undergo complete malolactic fermentation are susceptible to further activity if malolactic bacteria is present.
Filtration does not inherently decrease or increase wine quality. Some wines benefit greatly from filtration, while others may suffer do not require it. Filtration (not just whether or not to do it, but also how much to filter) is decided on a case-by-case basis. Wine quality can be diminished if wines are 'over-filtered'.
Although many winemakers may prefer to avoid filtration, the truth is that most have no choice due to the risks involved. Releasing a defective wine can be very detrimental to a brand. While smaller producers have more flexibility in managing the risks involved, it is imperative in larger production settings.