From elastic deformation to flow in tempered chocolate

We characterize the yield behavior and flow curve of a commercially available, molten, tempered milk chocolate with a fat content of 30%, from rheological measurements performed with a rotational rheometer fitted with a four-bladed vane spindle in a large-gap setup. We show that the yield behavior can be captured by the viscoelastic White–Metzner model, which indicates that elastic deformation precedes flow as the shear stress is increased. Following an initial fluidization cycle, the shear modulus of the tempered chocolate increases by a factor of 60 to G=4.4×104 Pa. We find that the Bingham model provides the best fit to our extensive flow curve data, where the yield stress is τyield=36.1±0.6 Pa and the Newtonian plateau viscosity is μB=8.7±0.02 Pa s.