A flawless wine is clear, this can best be determined especially with a white wine by holding the glass against a light source. With dark red wine this is of course difficult. Cloudiness in the form of clouds, haze or streaks is referred to in wine evaluations with the adjective blind and often indicates a more or less pronounced wine defect. Mostly this is caused by improper winemaking methods or lack of hygiene. The various reasons can be of a physical-chemical nature(proteins, tannins, crystals, metals) or biological nature(bacteria, yeasts) or are caused by substances foreign to the wine such as dust, filter material, cork dust and similar.