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Written by Charl Theron
Consumers have a basic requirement that wine should be clarified and contain no sediment or crystals. Apart from the fact that natural clarification of wines may take a very long time, the end result will not comply with the above-mentioned requirements. Filtration is one of the methods which may be used to clarify wine, but because it is a mechanical action, it should be done correctly.
If the filtration processes are not restricted to a minimum, the flavour, cultivar characteristics and mouthfeel of the wine may be affected negatively. During each filtration there is the possibility that thinning, product losses and unacceptable oxygen uptakes may ensue.If a small cellar considers filtration of wine, there should be clarity about the motivation for filtration, the affordability thereof, the availability of contract bottling and the analytical control that has to be executed before and during filtration.Apart from the consumer requirements with regard to the clarity of a wine, the correct filtration of wine can improve its ability to keep and its crispness. Potential taint can also be avoided because yeast and bacteria will be removed from wine through the appropriate filtration. The stage at which filtration is done will also influence the choice of method. Filtrations of juice before fermentation, a young wine after fermentation, red wine before barrel maturation or wine just before bottling differ considerably and should consequently be taken into account. If a wine is sterile filtered just before bottling, pre-filtration will be required to bring the degree of clarity below 1 NTU units.Once clarity has been obtained about the filtration process, the correct filter has to be selected. This choice will be determined by the motivation for filtration, wine quality, cost, effectiveness of the filtration process, versatility, filtration rate and possible future adjustments. Although a wide range of filter types and brands are available, a choice between lenticellular modular filters, cartridge filters, sheet and frame filters, drum filters and cross-flow filters should be sufficient to filter juice and wine. Each of these types has several advantages and disadvantages, which should be taken into account together with the cost of filtration, before making a final choice. If lees filtration is being considered, the choice will be limited to a vacuum drum filter and a sheet and frame filter.Sheet and frame filters that are packed with filter sheets offer a gentle filtration and can also deliver two different degrees of clarity during one filtration, but can unfortunately result in a leakage of 1 – 2% and also require 30 – 60 minutes’ preparation. If treating with steam for sterile bottling, the plastic frames may become misshapen or the rubber washers can harden in due course of time, leading to more wine losses.

FIGURE 1. A sheet and frame filter.
FIGURE 2. A cross-section of a lenticellular modular filter.

FIGURE 3. A cartridge filter.
FIGURE 4. A drum filter.

Lenticellular modular filters consist of a vertical bell-shaped, stainless steel jacket that is clamped to a base plate. It surrounds the circular filter discs which are stacked in modules. Preparation thereof is simple, it is easy to empty and minimal wine losses occur. It can also be filled with an acid metabisulphite solution for a few days, if the filtration process is interrupted. Although the filtration discs are more expensive than filter mats, the advantages of such filters make them very competitive compared to plate and frame filtration.Cartridge filters that also fit inside stainless steel jackets, offer the possibility of two different degrees of filtration during one process. There are limited losses, but the filter cartridges are expensive and it is essential to regenerate and store them correctly between different filtration processes so that they may be used again.Drum filters usually work with filter aids such as kieselguhr, perlite or cellulose, which are dosed at the same time as the wine flow, on a continuous basis. Although the capital cost thereof is high, operational cost is relatively low. If using kieselguhr, there are certain health and safety aspects which require attention and consequently perlite is more often selected as the filtration aid.Cross flow filters have a very high purchase and membrane replacement cost, which practically eliminates them as filtration equipment for small to medium cellars. Mobile filtration contractors may be considered in such instances. Ultra filtration is a very effective filtration process which can reduce the degree of cloudiness in wine to below 1 NTU and possible oxygen uptake is also limited to a minimum.If the decision is taken to buy a filter, questions about the following aspects should always be answered before committing to a purchase:

The availability of parts and applicable materials for filtration such as sheets, cartridges and filter aids.
The option of increasing the filter’s capacity and obtaining various degrees of clarity during the same process.
The storage and regeneration of filter cartridges.
The optimal flow rate and pressure to obtain specific degrees of clarity.

Before starting the filtration of wine and also afterwards the sulphur dioxide level and degree of clarity of the wine must be measured. The former will ensure that the wine is protected against oxidation and the latter to select the kind of filtration to be done and whether it was executed effectively. The accompanying Table 1 gives an indication of the different sheet filters that may be used.
Filtration of wine can be facilitated by racking red wines, which are not so sensitive to oxidation, three to four times a year. All wines will benefit from the correct use of enzymes and fining products during the crush, as well as the subsequent vinification processes (Howard, 2010) (Pregler, 2008).REFERENCESHoward, Cathy. 2010. Filtration for the Small Winery. Wine Business Monthly, September 2010: 30 – 31.Pregler, Bill. 2008. Product Review: Depth Filtration for the Small Winery. WINE 1 – 5.