Caking of sucrose crystals: Effect of water content and crystal size

White crystalline sugar after crystallization, centrifugation and drying Is generally stored in silos or conditioned in bags. It happens, relatively o ften, that caking is observed during silo storage or in the packages. To so lve the problem of caking, a systematic study of the parameters affecting i t should be undertaken. Among these parameters. water content, equilibrium relative humidity (ERH) and crystal size are the mast important. The water content in sucrose crystals of different cn stal sizes was determined using a Karl Fischer method adapted to the analysis of total water content by di ssolving a first sample of sugar at high temperature (50 degrees C) in a mo dified solvent. The surface water was determined by continuing the analysis In the same solvent saturated with sugar, using a second sample of sugar. analysis of the water content made possible the observation that internal w ater in the crystals is constant whereas surface ater content increases wit h relative humidity. The water content of sugar increases rapidly with decr easing rrl;stal size up to a particle size of 250 mu m. To account for the caking phenomenon. a method of measuring the friability angle was used. It made it possible to show that fine particles (250 mu m) cake at a relative humidity as low as 33%. Likewise adding 10% of fine particles to a standard sugar sample decreased the relative humidity of the beginning of caking fr om XO to 45%. It appears, then, that the prevention of caking involves avoi dance of the production of fine particles and to paying attention to the wa ter content and relative humidity during storage.