Modelling and experimental evaluation of high-pressure expression of cocoa nibs

The ability of the Shirato model to describe the expression of dry cocoa nibs in a hydraulic press at pressures of 20–80 MPa was compared with that of a numerically solved conservation laws model based on mass and momentum balances. Experimental data were used to determine the material constants involved in both models at 40, 80 and 100 °C. The Shirato model more accurately describes the final average porosity at different pressures. The Shirato model was therefore used to calculate the influence of the pressure, pressing time and mass of nibs used on the expression process. The calculation results followed the experimentally observed trends. The Shirato model was also used to describe the expression behaviour of cocoa liquor (finely grinded cocoa nibs) at 100 °C and pressures of 20–70 MPa. It was calculated that the filtration stage is absent at these pressures. However, the behaviour of cocoa liquor can only be accurately described with the Shirato model for the last part of the expression process (>100 s).