A mixing process is provided for the valorization of used cooking oils. The mixing process takes place in a particularly efficient way and includes supplying a given load (A) of used cooking oils and a corresponding load (B) of a solidifying composition to a mixing device. Thermal energy is supplied and in particular, an initial amount of thermal energy is supplied to cause the mixing temperature to reach a given temperature level. An additional amount of thermal energy is also supplied during a given mixing period. The solidifying composition includes a processing compound that includes at least two substances, one of which is of a wax type and the other is one of stearic acid, aromatic, coloring substances and additives.