Influence of shearing and time on the rheological properties of milk chocolate during tempering

The quality of chocolate is highly dependent on proper tempering. During tempering, crystals are formed as the chocolate is subjected to shear. The aim of this work was to evaluate the applicability of traditional rheological techniques to gain a better understanding of the relationship between rheological properties and the degree of shearing and time of tempering. Treatments of two shearing rates (15 and 30 s(-1)) covering four tempering times (0, 400, 600, and 800 s) were investigated. As samples were cooled from a melt temperature of 50degreesC, the apparent viscosity followed the Arrhenius equation. An induction time, which was affected by shear rate, was observed during tempering, followed by an increase in apparent viscosity, caused by formation of crystalline structures. Various characteristics of the rewarming curve were attributed to polymorphism. Steady-shear constitutive models assessed after rewarming showed that the yield stress was dependent on shear and tempering time. Collectively, findings showed that traditional rheological methods may be used as tools to investigate crystallization and flow properties of molten chocolate indirectly during tempering.