Modelling crystal polymorphisms in chocolate processing

Abstract

Efforts have been devoted over the last decades towards modelling phase change kinetics of fats in chocolate. The fats in chocolate have a number of polymorphic forms and manufacturers must deliver a product with the right polymorph to the consumer. In this work a model was developed that contains only two polymorphs rather than the six polymorphs that can be identified using Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD). This simplification allowed the phase change kinetics to be estimated from a set of DSC experiments. The phase change reactions were coupled with heat transfer and used to successfully predict the temperature profiles and the concentration of polymorphs (within 10%). These quantities determine among others contraction and cohesion, which are essential to demoulding and cleaning processes. Indeed, deposits left on the mould surface leads to undesirable product surface and an increase of cleaning costs. During the rapid cooling step (similar to the FrozenCone process), only a thin layer (to maintain the prescribed shape) of the shell is partially crystallised (typically 20% of the thickness) with unstable crystals (typically 10%) due to the high cooling rates. The model was then used to develop of a rapid cooling process allowing the estimation of the processing time required for the rapid cooling step depending on the thickness of the shell and the temperature of the plunger.