A method of regulating the viscosity of a mixture containing at least two components having different viscosities, which includes the steps of: (a) determination of the viscosity of the mixture via ultrasound measurements, (b) standardization of the viscosity determined to standard conditions, (c) comparison of the standardized viscosity with a prescribed intended value, and (d) adjustment of the viscosity of the mixture by increasing or decreasing the proportion of at least one component of the mixture, where the ultrasound measurements in step (a) are carried out at or in a line conveying the mixture or in a vessel.