possible to perform a mixing operation such as that shown in fig3 in this mixer indeed the pressure exerted by the piston 16 on the mixture 17 may be varied by raising or lowering said piston this consequently also allows variation of the power needed to provide rotation of the rotors 11 12 and therefore the energy used by the system the energy appears as an increase or decrease in the temperature of the mixture in order to carry out the method of the invention the indirect process parameters such as the energy used by the pair of rotors 11 12 are monitored during processing in a predetermined time sequence generally the time interval between two successive monitoring operations is lower than two minutes preferably not greater than 30 seconds and even more preferably not greater than 15 seconds so as to be able to correct in real time any oscillation within the predefined tolerance intervals where considered necessary or appropriate these indirect process parameters are monitored at even shorter intervals lower than one second during the different processing stages mentioned above so as to minimize the degree of deviation of the values of said parameters from the predefined nominal value at the start of the working cycle the piston 16 is fully raised so as to allow the introduction through a side hopper 18 of the mixer of a charge of material comprising at least one polymer or a mix of polymers a reinforcing filler comprising silica in combination with or instead of carbon black and a bonding agent for the white filler in this connection it must be pointed out that in the present description u201c white reinforcing.