Fat bloom formation on model chocolate stored under steady and cycling temperatures

In this study, two temperature cycling ranges, 20–29 °C and 20–32 °C, were used to promote bloom development on model chocolate, and control samples were stored at a constant 20 °C. Bloom formation was characterised based on visual inspection and surface colour analysis, while fat polymorphic transformation was monitored, and surface microstructure was examined. The control samples were highly bloom resistant and may exhibit solid-state polymorphic transformation. However, melt-mediated polymorphic transformation occurred under cycling temperatures; separated fat crystals formed on the chocolate surface under 20–29 °C cycling, while surface roughening occurred under 20–32 °C cycling, leading to differing bloom appearance. Additionally, the liquid fat content was higher when the temperature was cycled to 32 °C, than to 29 °C, and accordingly, bloom formation was also quicker. The pumping and capillary effects under the cycling temperatures led to fat migration to the chocolate surface, differing from the potential mechanism in the control samples.