In the final winemaking processes, the wine goes through some processes that aim to remove compounds that influence the colour and, consequently, the quality of the drink.
The wine clarification process consists in adding coagulant components to the drink in order to avoid the creation of residues (the well-known crystals in a natural substance) when the wine is in the bottle.
Normally, crystals appear in older wines, however, if this process is missing, residues may easily appear in any bottle.
The tartatic acid content of grapes varies little according to ripening, while malic acid decreases along ripening.
To evaluate the wine's tartatic stability, two tests can be performed:
This test is simple and quick and does not require any special equipment, however, it does not provide an accurate indication of the wine's degree of instability.
The test consists in storing the sample in a refrigerator for 4-6 days at 0ºC and then inspecting for the presence of crystals.
Another alternative is to place the sample in a freezer (-18ºC) for 8 hours. In this variant, the colloidal state is altered by freezing, and the precipitation of bitartrate much greater.
Mini contact" test
This test defines the stability of the wine, at 0ºC and in its colloidal state at the time of the test but does not predict colloidal restructuring in the wine during ageing.
The evaluation can be made by measuring the weight increase of the collected tartrate, or by measuring the drop in conductivity.
The rules governing stability are as follows:
Fall of up to 5% of the initial conductivity the wine is considered stable
If the drop in conductivity is greater than 5%, the wine is unstable.
It should be noted that the results of the mini-contact test tend to overestimate the stability of a wine.
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