Physical-mechanical method (also filtration, filtering and filtering) for the separation or purification of substances such as liquids or gases by means of technical filtering devices. Different filtration processes are a common process in the winemaking, Already in the antiquity there were at the Egyptians. Sumerians and Romans a technique in which wine was filtered by means of cloths or similar material. In the Middle Ages were added with acting as a filter piece of muslin fabric flavoring Spices filtered out of the wine. This piece of fabric was called "Manica Hippocratis" (sleeves of Hippocrates).
In today's viticulture the filtration mainly concerns grape and young wine, but also for the purpose of air disinfection and water, The purpose of this method is to remove unwanted substances and thus to stabilize or sterilize the grape must or wine. As a rule, this is done in several steps. First, the quite large ones created during pressing lees (Pulp) removed from the must (see under degumming and clarify ). Only so the so-called filter maturity of the wine is achieved as a prerequisite for the respective Filtrationsart. This means that the wine must not be too cloudy. A subsequent step is the removal of microorganisms as yeasts and bacteria,
However, not only those particles are retained by filters which (as one might assume) are larger than the filter pore size. Because that's just one of the effects. Other mechanisms include particle inertia, diffusion effects (thermal movement of particles), electrostatics with adsorptive Effect or barrier effect. Therefore, in principle, particles are deposited, which are far smaller than the pore size of the filter. In any case, filter pore sizes of ≤ 1 μm (millionth of a meter) are required (human hair approx. 40 μm).
Filtration can be done several times at different stages of winemaking, especially after Press (Most), after the fermentation as well as immediately before or at bottling, As a rule, several of the methods listed below also take place in combination. However, filtration always means a more or less strong mechanical load of the wine, it can also (too high) losses of flavorings or carbonic acid result, therefore, this method is to be carefully applied. In case of improper or too sharp application, this may be the case filter shock to lead. Many producers therefore largely refrain from filtration.
Starting from the USA For reasons of marketing on the label, in Europe too, in recent years, it is increasingly possible to point out " unfiltriert "(O. Ä.) Find. The alternative to filtration is the racking (Moving) from one container to another, which is certainly far gentler, but much more complex. Of the Beaujolais Nouveau is basically unfiltered wine. For wines with longer barrel aging automatically results in a better stability by the storage. Unfiltered wines form to a much greater extent depot (Sediment). For special wines like "sur lie" no filtration is carried out (see under lees ).
The unfiltered mixture of a liquid and finely divided solids is called suspension, the filtered product filtrate. Depending on the filter, the particles either due to the size (sieve effect) and / or due to adsorptive (electrostatic) effect excreted. There are a number of different filtration techniques, which are based on size, technical equipment and desired types of wine.
The filtration mechanisms and application techniques are divided into the following basic principles:
According to the location of the Trubrückhaltung one differentiates in surface or membrane filtration and depth filtration . In surface filtration, the filtered solids form a layer on the filter medium, the filter cake, In depth filtration, they are held in the depth (within) of the filter medium. There are the variants precoat filtration, layer filtration and Tiefenfiltermodule- / candles. After the liquid flow, a distinction is made between static and dynamic filtration .
Static filtration (also frontal or dead-end filtration): The flow direction of the liquid is vertical from top to bottom (vertical) through the filter area. All particles are retained either on the surface (surface or membrane filtration) or in the depth of the filter medium (depth filtration).
Dynamic filtration : The liquid is not passed vertically through the filter medium, but parallel or across a membrane surface. There is no dynamic depth filtration.
By a sharp filtration can thus also a fractionate done by wine. There are different substances like alcohol and flavorings separated and put together to a "new wine". However, this application is banned within the EU or very few applications such as alcohol reduction restricted, but in the New world usual (see under Spinning Cone Column ).
The most important of the many forms with different filter techniques and in detail different variants, which are often used in combination, are:
Membrane filtration : The static MF is mainly used for sterilization. This requirement is met if all potentially harmful microorganisms can be removed. Because of the low Trubaufnahmefähigkeit large surfaces are needed, which is why the membranes are usually accordion-like folded (pleated).
Cross-flow filtration (also crossflow filtration or tangential flow filtration): It is a dynamic filtration form. The name is derived from the direction of flow of the liquid. This is guided across a membrane surface (crossflow). Thus, the size range of the particles can be selected specifically. Depending on the particle sizes of the solids to be separated, micro-filtration (0.5 to 0.1 μm), ultra-filtration (0.1 to 0.01 μm) and nano-filtration (0.01 to 0.001 μm) are used μm). For sizes from 1 to 0.1 nm (billionths of a meter) one speaks of reverse osmosis (see under osmosis ).
The wine is pumped through the membrane at high speed. The filter cartridge consists of many asymmetrically constructed, hollow membrane fibers made of plastic in a vertically arranged filter housing. With newer models are no filter aids more necessary. The wine is repeatedly pumped through these hollow fibers in the cycle, a small, filtered part flows continuously sideways out of the housing, the greater part remains in circulation. The advantage of this technique is that the clarification (compared to all other techniques, where at least two operations are necessary) takes place in a single operation and a filtration is possible even at very high turbidity levels, such as in a still fermented young wine.
Precoat filtration : In the static depth filtration form, filter aids such as diatomaceous. perlite u. cellulose as well as powdered resins as ion exchanger used. These are first suspended in a liquid (dissolved) and then washed to the filter support. Once a sufficiently thick filter cake has built up, which then acts as the actual filter, is switched to the liquid to be filtered. Thus, a substantial removal of the smallest undissolved particles is possible. In addition, depending on the aids too adsorptive Effects are achieved.
Layer filtration : The static depth filtration form is predominantly used in Central Europe; in Austria about 90%. In contrast to Anschwemmform (where only one filter cake is built), there is a prefabricated filter bed. Depending on the application, this consists of a special mixture of filter aids such as cellulose, kieselguhr and / or perlite as well as resins, Depending on the mixture, special filter properties result. The only 3 to 5 mm thick layer results in a labyrinthine, closely meshed sieve with finest, countless branched channels. The wine flows through these channels relatively slowly. The mode of action results from a mechanical screening action and an additional adsorptive component.
Drum Vacuum Filtration (Vacuum Rotary Filter Filtration): In this mold, a rotatable drum is mounted in a tub surrounded by a close-meshed stainless steel screen cloth. In the tub, a mixture of water and filter aid (diatomaceous earth or perlite) is added. This is only suitable for must trub, not for wine.
The filtration residues (trub, yeast) are returned to the nutrient cycle in the vineyard, because organic matter predominantly nutrient humus character with high nitrogen content having. Larger amounts of filter aids reduce nutrient contents. But since a large-scale application in the fresh state is difficult, the residues are previously mostly after mixing with straw, bark, wood chop or rapecomposted, Excluded therefrom is the fining that results from a blue coloration, which must be discarded due to the cyano compounds contained in it (see under beautiful ).
Possible alternatives to filtration by means of various mechanical devices are flotation and centrifugation, Further procedures are under the keyword beautiful described. Complete lists of the numerous cellar techniques, as well as the wine-regulated wine, sparkling wine and distillate types are under the keyword winemaking contain. Comprehensive information under wine law is available at wine law,