A method for determining the bacterial charge in a liquid or semi-liquid product, comprising: - preparing a quantity of liquid or semi-liquid product to be analysed; - keeping that quantity of liquid or semi-liquid product at a preset measuring temperature (T m) and deriving values (α) representing an angle of electrical impedance of the liquid or semi-liquid product at predetermined time instants; - deriving a bacterial charge concentration in the liquid or semi-liquid product as a function of the time trend of the values (α) representing an angle of electrical impedance said method being characterized in that the phase of deriving a bacterial charge concentration comprises the following steps: - calculating a time derivative of the values (α) of the angle of electrical impedance of the liquid or semi-liquid product at successive time instants; - for each time instant of the successive time instants, comparing the derivative with a predetermined reference value to check whether that derivative is greater than the predetermined reference value; - if the derivative is greater than the predetermined reference value for one of the time instants, calculating, for that time instant, a value of bacterial charge concentration corresponding to that time instant using a predetermined relation between bacterial charge concentration and time, wherein the step of deriving values of angle (α) of electrical impedance comprises a step of generating a time-variable electrical voltage signal (Vref) in the liquid or semi-liquid product and a step of measuring in the liquid or semi-liquid product, an electrical current (lout) due to the electrical voltage signal (Vref). - preparing a quantity of liquid or semi-liquid product to be analysed; - keeping that quantity of liquid or semi-liquid product at a preset measuring temperature (T m) and deriving values (α) representing an angle of electrical impedance of the liquid or semi-liquid product at predetermined time instants; - deriving a bacterial charge concentration in the liquid or semi-liquid product as a function of the time trend of the values (α) representing an angle of electrical impedance said method being characterized in that the phase of deriving a bacterial charge concentration comprises the following steps: - calculating a time derivative of the values (α) of the angle of electrical impedance of the liquid or semi-liquid product at successive time instants; - for each time instant of the successive time instants, comparing the derivative with a predetermined reference value to check whether that derivative is greater than the predetermined reference value; - if the derivative is greater than the predetermined reference value for one of the time instants, calculating, for that time instant, a value of bacterial charge concentration corresponding to that time instant using a predetermined relation between bacterial charge concentration and time, wherein the step of deriving values of angle (α) of electrical impedance comprises a step of generating a time-variable electrical voltage signal (Vref) in the liquid or semi-liquid product and a step of measuring in the liquid or semi-liquid product, an electrical current (lout) due to the electrical voltage signal (Vref).