The measurement of raw sugar crystal size by sieving and by laser diffraction

Several methods for determining the crystal size of sugar are available. The paper reports the comparison of raw sugar size measurement by laser diffraction techniques as an alternative, or an adjunct, to the traditional sieve technique. Within Australia, and internationally, the sieve method has remained favoured because of its simplicity, reproducibility and its requirement for inexpensive equipment. The technique adopted varies from the use of a single sieve and base, which yields a percent fines value, to the use of multiple sieves from which mean aperture (MA) and coefficient of variation (CV) parameters can be estimated. or the laser technique, a relatively small sample size is required and the measurement time is relatively short. The paper reports results from trials which were conducted at several factories. Bulk samples of massecuite were removed from high grade batch pans at various stages of operation and centrifuged, without water wash, in a laboratory basket centrifugal to give a high pol sugar. The sugars were subsequently analysed by both techniques to determine size parameters. Correlations are tabulated for the sugars from the different factories, together with a global correlation, that allows conversion between the two size measurement methods for raw sugars with normal crystal morphologies. Data on the changes in the size distribution parameters that occur during growth to shipment sugar size are presented.