Why isn't wine vegan?
Such animal products are used, for example, during fining - after fermentation and ageing of the wine - to remove cloudy substances from the wine. Such trub substances are residues from winemaking and can be bound by proteins. These proteins are usually obtained from chicken eggs (egg white), milk(casein), animal bones, cartilage and skins(gelatine) or the swim bladders of fish(house bladder).
The proteins are aids in wine production and are filtered out of the wine together with the bound trub substances after fining. However, since they come into contact with the wine and react with it, residues cannot be completely ruled out. Therefore a wine is usually not vegan and may not be called so.
Vegan are and are called wines, which were beautified instead of with protein for example with mineral earth(bentonite). Vegetarian wines are only produced without the use of gelatine and fish bladder as fining agents.