Double Planetary Mixers incorporate more clean design features to help users improve the efficiency of high viscosity mixing processes. Traditionally equipped with rectangular-shaped paddles, double planetary mixers move batch material by rotating the blades on their own axes while they orbit on a common axis. At elevated viscosity levels, certain products tend to climb the rectangular stirrers and out of the mix vessel. This characteristic migration of batch material reduces mixing efficiency, necessitates intensive clean-up, and can even increase contamination risks. Helical blades prevent the climbing issue experienced with traditional rectangular stirrers. Other clean design features include highly polished stainless steel 316 wetted parts, labyrinth style gearbox sealing arrangement, double lip seals on each stirrer shaft, dust shield, flush mounted discharge valve and platen-style discharge system.