The effect of rapid cooling on the fat phase of chocolate

The aim of the project was to understand the science behind rapid cooling of chocolate used in the Frozen Cone® process. Differential scanning calorimetry was used to study the effect of slow and rapid cooling on tempered chocolate. On rapid cooling, lower melting polymorphs of cocoa butter were generated. Upon heating these recrystallised into the more stable Form V. Results were confirmed by similar observations with tempered chocolate fats. A hypothesis was formed whereby upon rapid cooling, lower melting polymorphs nucleate and grow at the expense of Form V nuclei produced during tempering. Upon subsequent warming, these polymorphs melt and recrystallise into Form V. Rapid cooling on untempered chocolate did not show any recrystallisation during warming; proving that tempering is required for the formation of Form V crystals in the final matrix. These results were confirmed by temperature-controlled X-ray diffraction on cocoa butter and chocolate fats. The polymorph generated upon rapid cooling was identified as Form I. This co-existed and eventually transformed to Form II and Form V upon warming. X-ray results showed that following rapid cooling, Form V crystals created during tempering did not grow until above 5 °C. Direct contact cooling at different temperatures was carried out to mimic the Frozen Cone® process. It was found that above -15 °C, the adhesion of the sample to the holder increases and seems to be correlated to the presence of Form II. These results suggest that the molecular structure and adhesive property of the polymorphs formed at specific temperatures are important for the release of chocolate. Stepscan differential scanning calorimetry was used to separate the simultaneous melting and recrystallisation events occurring in chocolate following slow and rapid cooling, by deconvoluting the total heat flow into reversing and non-reversing components. The general applicability and limitations of Stepscan DSC are also discussed