Measurement of yield stress in dark chocolate using controlled stress vane method

The controlled stress vane method was used to measure the yield stress in dark chocolate. Three vanes with different L/D ratios and five different stress rates were used in three different chocolate formulations. The vane displacement data did not indicate a definite yield phenomenon. When the vane displacement data were transformed into a ratio of vane velocity to elapsed time, the square root of vane velocity (SV) or the cube root of displacement, a definite yield phenomenon was observed. The SV was preferred on the basis of physical considerations and the linear regression of its derived yield stress on vane dimensions, stress rate and chocolate particle size. The value of the yield stress was the least when determined for a vane height to diameter ratio of 2 and at a stress rate of 3 Pa/min using the SV transformation.