Flow behavior and crystallization of sucrose solutions under process conditions of fondant production

Fondant is a valuable model for studying crystallization kinetics and flow behavior of highly concentrated sucrose dispersions under agitation. Despite its common use in confectionery, the interactions between supersaturation, crystal morphology, and viscosity are not fully understood. Simple experiments using a model system of pure sucrose solutions, a laboratory kneader, rheometer, and microscope provide insights into the key processes involved in fondant production and similar suspensions. Three main stages of the process are identified using two different stirring geometries and image analysis. In Stage 1, decreasing solute concentration during crystallization reduces suspension viscosity and instrument torque, independent of agitation geometry. Many crystal clusters form in both setups. In Stage 2, when a critical crystal volume fraction is exceeded, increasing collisions and inter-particle friction cause a torque increase in the kneader. In contrast, the rheometer setup enables crystal alignment, thereby preventing significant increases in torque. In Stage 3, counter-rotating blades in the kneader break clusters, leading to a torque peak and reduced mean crystal size, while in the rheometer, clusters and measured viscosity are hardly affected. These findings emphasize the impact of agitation geometry on torque and crystal properties, highlighting the importance of equipment choice for accurate measurements and product quality.