The criteria for the characterization of the classical fermentation processes: Submerged, Emerged and Solid-State Fermentations do not sufficiently describe all processes in those systems. Slurry Fermentation is an independent fermentation system that covers or encompasses processes that do not correspond to the classical systems and therefore require theoretical characterization. Slurry is understood as a two-phase, monodisperse system with a continuous liquid phase, characterized by a high suspension viscosity and a limited convective mass transfer. Three cases are distinguishable: (1) lower volume fraction, high suspension viscosity and diffusive mass transfer (2) high volume fraction, high suspension viscosity, and diffusive mass transfer and (3) high volume fraction, high suspension viscosity and micro-convective mass transfer.