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Wine Filtration

by Staff Writer - B. Shaughnessy | February 10, 2012

As wine is being enjoyed by the public at an ever increasing rate, it is not surprising that public taste and trend dictate how wine is made. Wineries all strive to produce an excellent product that consumers will enjoy. Failure to produce a reputable wine can lead to disaster. The end result of this scenario can be seen in the fact that it is difficult for a winery to remain in business if it has no customers.

One stage of the winemaking process that is heavily influenced by public tastes and trends is filtration. This is due to the fact that the public has been conditioned to expect certain properties found within the finished wine. Just as the stabilization process prevents the formation of superficial crystals, the filtration process modifies additional characteristics of the final wine. For example, a wine with naturally cloudy characteristics can be controlled and corrected using filtering processes. Like any process within winemaking, it is important to remember that the more a wine is handled the greater the chance for a loss of quality. Thankfully, filtration processes can be controlled to an extent where the final wine will show minute signs of quality loss.

The first question a vintner must ask is if filtration is needed and to what degree. As can be seen within the winemaking processes, different wines require different treatments. The filtration process follows the same logic. Some wines may require little filtration while others may require great amounts of filtration. Concerning the amount of filtration, modern technology has made it possible to filter out and separate the constituents that make up a wine. In this scenario it would be theoretically possible to blend these constituents in different ratios to make practically any form of wine. Thankfully this practice is illegal for wine production and is primarily used for research.

Almost all wines require filtration. The exception to this rule would be traditionally made wines. Wines made using traditional methods are stable once bottled, with any yeasts or bacteria dying out after the bottling process. For wines requiring filtration, red wines typically require less filtration than white wines do. Excessive filtration of red wines can lead to a condition where the body of the red wine is damaged due to depletion of red wine constituents. In sweet white wine production, filtration at greater levels is necessary to remove the yeasts and microorganisms that would otherwise convert the remaining sugars into alcohol (second fermentation).

Two different filtration principles are used with respect to winemaking filtration. These principles of filtration center on the method of particle extraction. The filtration methods are known as depth filtration and surface filtration. In depth filtration, the filtering medium is composed of tiny channels which wine is circulated through. During the circulation of wine, particles collect on the walls of the channels before the wine has exited the filter medium. Depth filtration has numerous advantages with primary advantages being performance and expense. Depth filtration can easily remove course particles from a wine at a relatively inexpensive material cost. The filter medium used with depth filtration is known as kieselguhr or diatomaceous earth. Pads of filtration material also are available that have the same properties as diatomaceous earth but are more expensive than diatomaceous earth. The disadvantages with depth filtration are that it is fairly easy to disrupt the filtration process and force removed particles back into the wine. Equally important is the fact that depth filtration is not an effective filtration method for removing fine particles from the wine.

The devices used in conjunction with depth filtration are known as a rotary vacuum filter and a plate and frame filter. With a rotary vacuum filter, a large stainless steel small-pored mesh drum is rotated horizontally in a vat of wine. Diatomaceous earth is added to the wine and circulated through the small openings in the drum. Over a short period of time, small particles of diatomaceous earth collect on the surface of the mesh. The collection of diatomaceous earth forms a layer approximately 1 inch (2.54 cm) thick. At this thickness, the wine is pumped through the diatomaceous earth where particles have collected. The outer layer of diatomaceous earth is continually scraped off and discarded while the pumping action continues. Due to the damaging effects of oxygen, rotary vacuum filters have been designed to operate in an oxygen free environment.

Plate and frame filters are also used with depth filtration processes. Essentially, plate and frame filters consist of racks of sheeted filter material pressed between plates roughly the size of small windows. Wine is circulated through these plates with particles being trapped in the depth of the filter. As with rotary vacuum filters, plate and frame filters can be designed for use in an oxygen free environment.

With the known limitations of depth filtration, it is not surprising that surface filtration systems were developed. Surface filtration systems utilize a filter element where the pores of the element are smaller than the particles being filtered. As implied by the name, particles are collected on the surface of the filtering element while the wine passes through to the other side of the element. Advantages to surface filtration systems are the ability to remove very minute particles found within the wine. The main disadvantages of surface filtration systems are filter life and cost. As particles become trapped on the surface of the filter, the amount of time a filter can effectively remove particles is limited. Also, the cost of the filter elements is considerably higher than the filter medium used with the depth filtration method. The nature of the surface filtration method results in surface filtration devices being simpler when compared against depth filtration devices. Cartridge type filter elements are easily installed into pumping manifolds where the wine is circulated.

Most wineries use both depth and surface filtration systems or a special variant of the surface filtration system. When using both depth and surface filtration systems, depth filtration is first used to remove large abundant particles. Surface filtration is then used to remove subsequent smaller particles. Some wineries are investing in a new surface filtration process where particles are encouraged not to collect on the surface of the filter element. This is achieved by orienting wine flow to be parallel to the filter element. In this set-up, the force of the moving wine whisks particles off the surface of the element.

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