Term for the subjective, optical impression of a solid, gas or liquid that is transparent in its "normal state". It is caused by small particles that have a refractive index that differs from that of the carrier material or that cause adsorption. In the past, the turbidity of a liquid was measured with a transparent container. On the back of this was a viewing panel (similar to an eye test at an ophthalmologist), which was viewed through the liquid. The number that could just be read corresponded to the measured turbidity. However, this method was very imprecise and also dependent on the eyesight and additionally on the subjective feeling of the test person. In order to be able to measure turbidity in a comparable way, the turbidity standard liquid Formazin was created. Turbidity units are FAU, FNU, FTU and TE/F (in water treatment) as well as EBC (European/international unit, used in brewing for beers).
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Diplom-Sommelier, Weinakademiker und Weinberater, Volders (Österreich)