Chocolate masses are one of the basic raw materials for the production of confectionery. Knowledge of their rheological and flow behaviour at different temperatures is absolutely necessary for the selection of a suitable technological process in their production and subsequent processing. In this article, the rheological properties (the effect of the shear strain rate on the shear stress or viscosity) of five different chocolate masses were determined—extra dark chocolate (EDC), dark chocolate (DC), milk chocolate (MC), white chocolate (WC), and ruby chocolate (RC). These chocolate masses showed thixotropic and plastic behaviour in the selected range of shear rates from 1 to 500 s−1 and at the specified temperatures of 36, 38, 40, 42, and 44 °C. The degree of thixotropic behaviour was evaluated by the size of the hysteresis area, and flow curves were constructed using the Bingham, Herschel–Bulkley and Casson models with respect to the plastic behaviour of the chocolate masses. According to the values of the coefficients of determination R2 and the sum of the squared estimate of errors (SSE), the models were chosen appropriately. The most suitable models are the Herschel–Bulkley and Casson models, which also model the shear thinning property of the liquids (pseudoplastic with a yield stress value). Using the coefficients of the rheological models and modified equations for the flow velocity of technical and biological fluids in standard piping, the 2D and 3D velocity profiles of the chocolate masses were further successfully modelled. The obtained values of coefficients and models can be used in conventional technical practice in the design of technological equipment structures and in current trends in the food industry, such as 3D food printing.

The chocolate mass behaves like a typical non-Newtonian plastic liquid defined by the yield stress and the plastic shear stress. The rotary rheometer with a cone-plate spindle system was chosen to determine the flow properties of chocolate masses. The effect of shear stress on shear deformation rates was measured at a temperature of 40 °C in an ascending mode from 1 s^–1 to 500 s^–1 for chocolate samples [white chocolate (WC), ruby chocolate (RC), and caramelised Amber chocolate (AC)]. Plastic models, according to Casson, Bingham and Herschel-Bulkley, were used for the mathematical description of this dependence. The Herschel-Bulkley model was evaluated as the most suitable mathematical model for describing the flow behaviour of unconventional chocolate masses. The Herschel-Bulkley model was chosen based on a high value of the coefficient of determination R² and a low value of the sum of the square error estimate (SSE). The non-Newtonian plastic behaviour was confirmed, and the yield stress was determined for all types of tested chocolate masses.

No abstract

No abstract