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Filtering wine: how and when

Filtering wine serves to remove residues and solids: here is how and when to do it correctly.
The complete guide to correct wine filtration
In assessing the quality of a wine, clarity plays a fundamental role: the absence of turbidity makes it possible to recognise a fine wine even without uncorking the bottle. It is the result of careful wine filtration and clarification work, carried out by master vintners through a meticulous and gradual process involving several stages.
Understanding how wine is filtered, what techniques are most commonly used in the most renowned wineries, or witnessing the wine production processes first-hand on a guided tour of a historic winery such as Banfi, we are sure will be a source of enriching knowledge about the world of wine for our visitors.
How to filter wine and why
Filtering wine, red or white, has the purpose of increasing the clarity of the product, removing suspended elements that may cloud its appearance or, in some cases, compromise its quality and bouquet.
In practice, wine filtration consists of separating the liquid from the solid residues (lees, yeasts or other granular particles) that may remain on the bottom after pressing or fermentation. This process is carried out with the use of special filtering tools, made of different materials and often enriched with substances that increase the filtering capacity.
Wine filtration techniques
The different filtration techniques, depending on the grain size of the particles to be removed, are divided into:
coarse filtration techniques: these are used to remove the more voluminous particles in suspension in the wine;
sparkling filtration techniques: they intervene on the smallest particles, those visible especially in white wines or fine productions where even the smallest sign of turbidity can compromise the quality of the product;
sterilising filtration techniques: they completely eliminate microorganisms in the wine, including potentially harmful yeasts, thus stopping the fermentation process at its ideal point.
The methods used when filtering wine
Speaking of how wine is filtered, it is interesting to know that in large wineries, two main methods can be distinguished:
The first is called sieving or surface filtration: it consists of filtering the wine through a series of porous surfaces that retain impurities on the surface, since they are larger than the filter holes;
the second is called absorption or depth filtration: it involves the use of absorbent fibres that retain sediments and particles inside them, thus allowing only the wine that has now clarified to filter through.
There are therefore different wine filtration techniques that also differ in the type of materials used during the process. The choice of filters depends mainly on the characteristics of the wine and the degree of limpidity one wishes to achieve. Furthermore, wine filtration techniques can be performed successively in order to achieve satisfactory clarity depending on the wine being treated.
Filtration with deposit
Deposit filtration is the first to be performed and has a coarsening effect. Its purpose is in fact to remove the coarsest particles through the use of a cloth. It is one of the most widely used methods for filtering wine at home.
Flood filtration
Continuous flood filtration cleans the wine of fermentation sediments (lees, skins and yeasts). A perforated panel with fairly large pores is used; these are filled with cellulose and silicates, materials that activate and intensify the filtration process.
The advantage of this method is that it can work on large quantities and fully utilise the effectiveness of the filter aids.
Filtration on cartons
Filtration on the cartons takes place by means of biodegradable and compostable cellulose panels, enriched with cotton fibres, kieselguhr and cationic resins. The panels are sandwiched between two perforated plates and the depth filtration method is used: the cartons absorb and retain the main impurities.
Membrane filtration
Membrane filtration (or 'microfiltration'), on the other hand, is intended for wines that must respect a high degree of limpidity. Very thin membranes capable of retaining microscopic particles are used, made of both organic (polymeric membranes) and inorganic (ceramic membranes) materials.
Finally, when the flow of the liquid is parallel to that of the membrane and minimises deposits on the membrane, we speak of tangential filtration.