The monitoring of the pomace pre-fermentation process is carried out visually, for which it is necessary to stop the pre-fermenter to extract a sample. This paper presents a novel method of automatic fuzzy monitoring of the process, using the value of the active power of the squirrel cage motor that drives the mixing agitator. The proposal is based on the fact that at the beginning the pomace contains solids in the mixture, which present opposition to the rotation of the agitator, and while the process progresses, must is released, so the three-phase squirrel cage motor requires developing less torque in the axis, which generates a lower value of active power consumed. Finally, simulation and experimental results are presented.