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Diatomaceous earth filtration

Special filtration technique; see under filtration.

Physical-mechanical process for separating or purifying substances such as liquids or gases using technical filter devices. Various filtration methods are a common process in winemaking. Even in ancient times, the Egyptians, Sumerians and Romans used a technique in which wine was filtered using cloth or similar material. In the Middle Ages, a piece of muslin cloth was used as a filter to remove the added flavouring spices from the wine. This piece of cloth was known as the "Manica Hippocratis" (sleeve of Hippocrates). It was used to make a drink known as hypocras, which is similar to mulled wine and is still produced today according to an old recipe.

Filtration - Hippokrates, Manica Hippocratis, Hypocras

Purpose of filtration

In modern viticulture, filtration mainly concerns grape must and young wine. The purpose is to remove undesirable substances and thus stabilise or sterilise the grape must or wine. This usually takes place in several steps. Firstly, the rather large lees (pulp) produced during pressing are removed from the must (see also degumming and clarification). Only then is the wine ready to be filtered as a prerequisite for the respective type of filtration. This means that the wine must not be too cloudy. The next step is the removal of microorganisms such as yeasts and bacteria. However, filtration does not only have advantages, as this means a more or less strong mechanical load on the wine. The fine particles and suspended particles are also flavour carriers, and removing them can also result in (excessive) losses of aromatic substances or carbon dioxide. The method must therefore be used with care. If used incorrectly or too harshly, this can lead to filter shock.

Time of filtration

Filtration can take place several times at different stages of winemaking, especially after pressing (must), after fermentation and immediately before or during bottling. As a rule, several of the processes listed below are also carried out in combination. However, filters do not only retain particles that are (as one might assume) larger than the filter pore size. This is only one of the effects. Other mechanisms are particle inertia, diffusion effects (thermal movement of particles), electrostatics with adsorptive effect or barrier effect. As a result, particles that are far smaller than the pore size of the filter are also separated. In any case, filter pore sizes of ≤ 1 µm (millionth of a metre) are required (a human hair has a circumference of approx. 40 µm).

Alternative to filtration

Starting in the USA, the words "unfiltered" (or similar) can increasingly be found...

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