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 x 10(4) Pa. We find that the Bingham model provides the best fit to our extensive flow curve data, where the yield stress is tau(yield) = 36.1 +/- 0.6 Pa and the Newtonian plateau viscosity is mu(B) = 8.7 +/- 0.02 Pa s. (C) 2018 The Society of Rheology.