The objective of this work is to characterize various deformations to which viscous pastes are subjected during their batch mixing and to investigate the influence of mixer configurations and operating conditions. For this, several mixer geometries were modeled in a way representative of the mixing mechanisms taking place. The twin-blade arrangement, which is typical in batch mixing, was used in this study, as well as planetary mixers. The equations governing the deformation of the fluid were solved in the various mixer geometries, using numerical solution techniques (finite-element discretization on a fixed mesh, with a fictitious domain method accounting for the internally moving blades). Based on the time-dependence velocity fields obtained, the type of deformation taking place in various mixers was characterized using relevant kinematic flow classification parameters. These parameters were then related to the mechanical action of the mixer.