© 2018 Elsevier B.V. This study presents a new rheometry technique which requires a free surface velocity field as an input. By minimising the difference between observed and simulated data, we show here that it is possible to estimate the three parameters of an assumed Ellis rheological law. The dam-break problem is considered here with molasses as the working fluid. The free surface velocity is evaluated by seeding the free surface with buoyant particles and using particle tracking velocimetry. The parameter identification is successfully tested with “synthetic” data produced by the numerical model. The parameter identification algorithm is shown to be robust even when significant noise is added to the synthetic dataset. For true experimental data, the reconstructed flow curve is within 25% of the actual one, demonstrating the potential of the method for circumstances where standard rheometry does not apply.