Dark chocolate's compositional effects revealed by oscillatory rheology

In this study, two types of oscillatory shear rheology are applied on dark chocolate with varying volume fraction, particle size distribution, and soy lecithin concentration. The first, a conventional strain sweep, allows for the separation of the elastic and viscous properties during the yielding. The second, a constant strain rate sweep, where the strain rate amplitude is fixed as the frequency is varied, is analyzed to obtain Lissajous curves, dissipated energy, and higher order nonlinear contributions. It is shown that chocolate exhibits complex nonlinear behavior, namely shear thinning, shear thickening, and strain stiffening. The effects on this behavior related to volume fraction, particle size distribution, and lecithin concentration are investigated, and comparison with simple monodisperse hard-sphere suspensions is made.