ASSESSING THE EFFECTS OF THE CONCHING PARAMETERS ON THE FLOW BEHAVIOR OF MILK CHOCOLATES

Conching is a critical step in chocolate manufacturing, responsible for the refinement of aroma and the development of the flow properties of the finished product. It involves continuous heating, aeration, and shearing of the mass, serving as a thermomechanical catalyst for physicochemical and microstructural changes, such as residual moisture removal, fat redistribution, and improved particle packing. Despite its importance to chocolate quality, it remains the lengthiest, most energy-intensive, and least understood operation of chocolate processing. This study aims to shed light on the influence of the pasty conching parameters on the rheological properties of a model milk chocolate. A fractional factorial design 2^4-1 was employed to systematically evaluate the effects of four independent variables at two levels each – conching time, temperature, conching speed, and fat content – on the flow characteristics of the chocolate mass. The response variables were moisture content, Casson plastic viscosity (ηca), Casson yield value (τca), and the conche’s total energy demand. Three repetitions at the central points were done to monitor experimental error and any deviation of the levels from linearity. No thixotropy was detected in any of the samples, suggesting that all investigated levels of the parameters were sufficient to develop the flow properties of the model milk chocolate. Conching time exerted a stronger negative effect on Casson plastic viscosity, while temperature exhibited a stronger negative effect on Casson yield value. Normally, plastic viscosity is more sensitive to shifts in the free fat content of chocolates than yield value, which is more critically affected by changes in the microstructural interaction between particles. Significantly lower moisture contents were also observed under higher temperatures. The increased moisture removal might have weakened the interaction forces between particles, thereby reducing yield value. Moreover, fat content showed highly significant (P < 0.05) positive effects on both plastic viscosity and yield value. The higher the fat content in the plastic mass during pasty conching, the lower its resistance to shearing, which leads to lower energy input. This was further supported by the strong negative effect of fat content on the conche’s total energy demand. Overall, this study brought additional evidence linking the conching parameters to the rheological outcomes in milk chocolates. Finally, it may guide manufacturers in the choice of the most suitable processing conditions to achieve adequate flow properties in their products while saving time and money.