Crystallization in highly supersaturated, agitated sucrose solutions

Supersaturated sucrose solutions that have been sufficiently cooled without nucleation represent a metastable system in which agitation promotes fast crystallization. Applications of this physically interesting process can be found, for example, in the production of fondants in confectionery. This work considers supersaturated sucrose-water solutions under agitation, different temperatures, and concentrations as simplified fondant model systems. Although simple in composition, such solutions undergo complex kinetic and thermodynamic processes during crystallization under agitation. Main attention is paid to the torque during constant kneading of the samples at controlled temperature, accompanied by light microscopic examination of a characteristic sample. All torque curves show a characteristic minimum followed by a sharp peak during crystallization, which are attributed to an interplay of changes in concentration of the continuous liquid phase, formation of big conglomerates, and breaking of largest particles during continued growth. When comparing the crystallization times with classical nucleation theory, it is found that the variations are related to temperature and supersaturation in the same way as given by induction time models of thermodynamics and statistical physics.