SOME CONSIDERATIONS ON THE PHYSICAL SIGNIFICANCE OF TURBIDITY ESTIMATES

Abstract

The turbidity of a hazy substrate is an optical concept based not upon the nature the haze but upon its appearance; it is defined in terms of that proportion of the light falling upon the substrate which is scattered by it. Light scattering is known be a rather complex phenomenon the precise character of which is determined only by the concentration of the scattering material, but by its physical properties, above all by its state of subdivision. In particular, the angular distribution of scattered light is non-uniform and dependent upon the size and shape of the scattering particles. A critical examination of some current methods of estimating turbidity shows that none of them is—nor can be—perfect. Discrepancies between them are inevitable and must therefore be accepted. Neither can there be, in general, any really close correlation between turbidity as measured in the laboratory and the consumer's appraisal of the clarity of beer since the latter is not, even in principle, based upon any simple, defined physical concept. Notwithstanding these reservations, it must be stressed that turbidity measurements in the brewery laboratory are in valuable and irreplaceable. An experimental study has shown that the discrepancies which may be expected between different methods when these are used to measure diverse kinds of turbidity are large and readily observable; in the case of beer they may easily reach a magnitude of 50%.