The purity and age of a wine can be judged through its limpidity. A young wine is particularly brilliant, while a very mature wine is often rather opaque.
If a young wine is cloudy and reveals particles in suspension or sediment of white tartrate at the bottom of the glass, it means the vinification process has failed. In white wines, extreme brilliance indicates a wine of exceptional quality. Because of its intense colours and tannins, it is impossible to judge the limpidity of a red wine.
The limpidity of a wine can be judged by holding the glass up to a light source, natural if possible.
White wines and roses that reflect the light are considered brilliant. This is the sign in a young wine indicated that the filtration that contributes to the purity of colour has been perfectly effected.
A slightly less luminous wine is said to be crystalline. On a scale of limpidity, this is still an indication of quality. In fact, after a few years of aging, a brilliant wine becomes pure and crystalline, like spring water.
In a red wine, richer tannins and more brightly coloured than a white wine or a rose, the degree of excellence of colour cannot reach that of brilliant or crystalline, with the exception of wines made with carbonic maceration. This is done without added yeast, and the grapes are not pressed; the oxygen is eliminated in an anaerobic atmosphere through the use of carbon dioxide, as in wines from the Beaujolais.
A red wine is at its best when it is judged simply limpid. Applied to a young white wine, however, this adjective implies that there is probably a problem of filtration, particularly if the wine is a straw yellow or green colour.
An aged white wine that displays a colour with hints of amber may be limpid or even slightly cloudy without implying an inferior quality. The term can also be used to describe aged red wines whose tannins decompose at maturity, giving it a cloudy aspect. This is one of the reasons why wine is decanted from the original bottle, to separate it from its sediment.
When a wine is cloudy, a term that is invariably negative, its haziness indicates that it has suffered and error of vinification, has been poorly stored, or is at the end of its life.
Limpidity is linked to the techniques used in the cellar and to the age of the wine. During the first year, part of the vinification process of red wines involves racking, a process in which suspended matter that has settled at the bottom of the barrel are separated by transferring the wine from the original cask into a clean and sterile one. The following stage, clarification or fining (the introduction of organic agents such as egg white or gelatine, which attract the remaining minute particles) also ensures that the wine will be perfectly clear.