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SCHANDELMAIER Inquiring Winemaker The Hidden Life Of Filter Cloths By Bernhard Schandelmaier Editor���s note: Tim Patterson is on temporary leave from writing the Inquiring Winemaker column while he works on his next book. Winemaking researchers, teachers and professional winemakers will be contributing to this page during his absence. T he use of filters with juice lees has been a worldwide standard for many years. Filter presses are used for separating solids from liquids in many industries. In the wine industry, the filter press (depending on its use) usually is referred to as a lees filter. The lees filter is especially suitable for coarse purification and results in very low residual moisture values in the cake. A pump is used to feed a mixture of filter aid and lees into the chambers of the filter press. The liquid in this slurry passes through the filter cloths and exits through the filtrate outlet. In an ideal filtration, the filtrate can flow freely. Yarns and weave structures influence the ease of cleaning filter cloths and determine its resistance during filtration. The permeability of the fabric to cleaning solutions and the fineness of its mesh affects the amount of lees that gets embedded while pre-coating the filter cloth, increasing the resistance during filtration and promoting the growth of microorganisms in the filter cloth during storage. Until recently, however, winery customers have had little choice in filter cloths. Conventional filter cloths have been very fine mesh of low permeability and difficult to clean thoroughly. Often, filter cloths are kept as long as the filter itself, replaced only if punctured beyond repair. 138 W in e s & V i ne s JANUARY 20 13 Black dirt remains on a multifilament cloth after a standard cleaning; note the carbon deposits resulting from a fining. Water adheres to a multifilament cloth. The past eight years have seen a movement in the market, and today a wider range of filter cloth is available. The filter cloths differ in the types of yarn and in weave structures. One especially useful innovation is a modern monofilament cloth being used commercially in German, Austrian and Italian wineries that improves lees filter performance and cleanliness. Types of yarn The most common types of yarn filter cloths are manufactured out of multifilament or monofilament yarn. These types of yarns also may be woven or mixed. Conventional filter cloths are made of a fabric of multifilament yarn, which consists of several filaments twisted together to form a continuous plastic wire. Fabrics made from such yarn are very durable, because a break in a single fiber has almost no impact on the overall stability of the material. However, the large number of threads creates many spaces where solids can settle. The more solids that settle into the cloth interior, the more microorganisms can proliferate using lees as a food source. The deeper the sediment particles are located in the cloth, the more difficult they are to remove. This may be one of the reasons that several days can sometimes be necessary to achieve a complete cleaning of the cloths. In addition, in the very dense, finely woven filter fabrics, the water is held by capillary action and will not drain, encouraging in consequence the continued growth of microorganisms. Particulate entry also is favored when there is no pre-coat filtration with clean must, and the turbid particles can therefore act on the filter cloths right from the beginning. This is typically the case in initial juice filtration until clear juice is generated for use in pre-coating���a catch-22. Conventional multifilament filter cloths are finer than necessary merely to support the filter cake, and turbid particles enter into the filter cloth until a thick enough filtration layer has been built. These effects can add up until initial filter backpressure becomes surprisingly high and Highlights ��� he author has studied the benefits of T monofilament filter cloth vs. conventional multifilament in filter presses. ��� he fine mesh and low permeability T of conventional lees filter cloths make them difficult to clean thoroughly. ��� onofilament fabrics, though hard to M find in North America, perform better and clean more easily and completely.