Term (French louche = opaque, disreputable, suspicious) for an aniseed spirit becoming milky when water is added or also very strong cooling. These include the branded spirits absinthe, pastis and pernod (France), aguardiente and pacharán (Spain), aquavit (Scandinavia), arrack (East Indies), ouzo and tsipouro (Greece), and raki (Turkey). However, the phenomenon is often called the "ouzo effect" after the Greek liquor.
The Louche effect can be used to compare the aniseed content of these drinks. This is because the cloudier the liquid becomes at a certain mixing ratio, the more aniseed is contained in the spirit. The addition of water opalesces the clear liquid. The milky cloudiness is formed by an oil-in-water emulsion that causes light scattering. The cause of the effect is the poor water solubility of the essential oil anethole contained in absinthe. It is therefore not a chemical but a physical phenomenon. The effect can also be achieved (without adding water) by cooling down the spirit. The phenomenon is also known in nature as the Tyndall effect. It occurs mainly on sunny afternoons in late summer. The sunlight is refracted by tiny particles in the air, giving the impression of a golden mist over the landscape.
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