Influence of local convective heat flux on solidification, contraction and wall detachment behavior of molded chocolate during air cooling

Abstract

The cooling process is an important step during chocolate production. It influences final product quality characteristics such as gloss, texture and melting behavior. Furthermore, it is a high energy consuming operation and its optimization leads to an increase in energy efficiency of the chocolate production. Dark chocolate was cooled in a pilot-scale cooling tunnel with cooling air temperatures of Tair = 2, 12 and 18 °C and air mean velocities of vin = 1.5, 3.5, and 6.0 m s−1. Convective heat transfer coefficients at the top and the bottom of the mold were received from model calculations applying a CFD model. Crystallization and detachment behavior from the mold walls were newly analyzed by measuring the damping characteristics of ultrasound waves transferring the filled molds during cooling. In addition, for this-like treated well-tempered dark chocolate, the crystallization and detachment behavior were analyzed in further detail. The convective heat transfer from the bottom of the mold increases in flow direction due to the existence of a typical mold geometry-dependent recirculating zone of the cooling air below the chocolate mold and also dependent on the local air velocity. It was shown that depending on intensity and homogeneity of the heat transfer in the air-cooling phase, the structure density of the chocolate can be increased which has a positive impact on resulting product quality characteristics. Moreover, the detachment of the chocolate from the mold wall was demonstrated to have an optimum for typical chocolate plate formats with 125 g weight at an apparent heat flux of 550 W/m2, for which the time until detachment reaches a minimum.