Filter Presses and Cloths for "Lees Filtration"
How the Filter Press is Used in Winemaking
Filter presses are used for separating solids from liquids across many industries and applications. In the wine industry, the filter press is often referred to as a “lees filter.”
Lees is the sediment at the bottom of fermentation vessels and includes solids such as grape skins, pulp, stems, seeds and residual yeast. Lees can represent up to 10% of a winery’s total volume, which can be a significant amount in a larger winery. Lees also contain a high percentage of recoverable product, with solids concentrations typically in the range of 20-30%, which lends itself well to dewatering via filter press.
A filter press is also well-suited for this type of application as the lees filtration process generally results in a filter cake with low residual moisture (a relatively dry cake). The lees slurry is usually combined with a filter aid such as DE (Diatomaceous Earth) and fed into the filter press using an AOD pump.
The Role of Filter Cloths in Lees Filtration
Filter cloths also play an important role in lees filtration. However, for many years wineries had few choices in the type of materials available. Traditional winemaking filter cloths have been composed of very fine mesh with low permeability and challenges in cleaning. Filter cloths were usually kept as long as the press itself, replaced only if damaged beyond repair. (Source: Wines & Vines, Jan. 2013).
Multifilament Filter Cloths
More recent polypropylene filter cloths have been made of multifilament threads, which are grouped together to form a single strand, or “yarn.” Multifilament fibers feature good particle retention and are very durable, since a break in a single thread has very little impact on the overall stability of the cloth.
However, the large number of threads create many spaces where solids can settle into the interior of the cloth, which can cause clogging (blinding). This can also lead to the proliferation of microorganisms using lees as a food source. The deeper the particles are embedded in the cloth, the more difficult they are to remove, causing challenges in cleaning.
During the past few years, the market for winemaking has generated a wider range of available fabric types, including monofilament and mono-multi cloth materials.
Monofilament Filter Cloths
Monofilament filter cloths utilize individual round, continuous single-core plastic wire to form the cloth. This provides for a very smooth surface, with low particle retention and excellent cake release characteristics. These cloths also have the advantage of being more permeable, allowing for higher flow rates.
Because there are less spaces where solids can settle, they are less likely to become blinded, and are much easier to clean. The only drawback to monofilament cloths is in their durability. Because these cloths are woven from individual strands instead of multiple fibers woven together they are more fragile, and a crack in a single strand can compromise the stability of the entire cloth.
Mono-Multi Filter Cloths
Mono-Multifilament fabrics combine the benefits of both mono and multi to get the best of both worlds. That is, the excellent cake release, higher flow rates and ease of cleaning of monofilament, plus the durability of multifilament fibers.
M.W. Watermark has a team of experts on staff that can help you determine the best solid-liquid separation equipment and filter cloths for your particular application. We have an in-house laboratory where we can test your slurry sample and recommend the best pre-treatment, equipment and filter cloths to form an ideal filter cake.
Contact M.W. Watermark to learn more or for a quote.
Visit our Filter Cloths 101 page for FAQ’s, additional blog links, filter cloth terms and more information on materials.
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