Researchers at Cadbury Ltd. and University of Birmingham (UK) are using FIDAP to increase their understanding of the thermal behavior of chocolate during manufacturing processes. They have found FIDAP to be a useful tool for improving process conditions, designing new candy products, and for troubleshooting heat transfer and materials problems. The modeling of heat transfer in chocolate is difficult because its physical properties are not available in the literature and can vary quite widely, depending on the recipe. Reliable values are needed for the thermal conductivity and specific heat. These can be a function of the processing history (e.g., shear rate and temperature).

Did you know that there are six different crystalline forms of chocolate? No, we don’t mean milk chocolate, semi-sweet, and dark! The cooling rate determines which solid chocolate type is formed. The most desired form, so-called Type V, is created by a very slow cooling rate and results in a hard glossy product that melts in the mouth, but not at room temperature. However, if the chocolate undergoes further temperature cycling during storage, Type VI crystals can be formed, which exhibit a characteristic “white bloom”. This bloom is only cocoa butter and is not harmful, but it is clearly undesirable from the customer’s viewpoint.

Collaborative work with Dr. A. Shapley at the University of Birmingham (UK) has been ongoing for the last three years to establish reliable physical properties. Differential scanning calorimeter tests show that the cooling rate not only lowers the temperature at which the chocolate crystalizes but also lowers the total amount of latent heat evolved (a new finding). Previous research studies in this area have assumed that the total enthalpy of the sample does not vary with cooling rate. The effective specific heat model was then incorporated into FIDAP using a user-defined subroutine.

Finite element mesh of the coffee creme center and temperature distribution in the coffee creme center of a Cadbury chocolate candy during manufacture.

To gather experimental data to validate the model, a test mold containing five thermocouples was constructed. The mold was filled with molten chocolate and cooled in a pilot plant cooling tunnel. Temperatures throughout the sample were measured versus time for different cooling rates. The temperatures predicted by the FIDAP model were in excellent agreement. The model was also validated with data obtained from a soft-center production line at Cadbury.

FIDAP is now being used to predict the effect of changing plant conditions and different production facilities. Plans are being made to use “chocolate fluid dynamics” to design the cooling conditions for new candies before production trials begin. This will ensure that the new products are mouth-watering and delicious right from the start.

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