Abstract: A method and apparatus for continuously monitoring and controlling the composition of a stream of milk is disclosed. A portion of the continuous stream of milk is heated and coupled to a vacuum degasser where the gas in the milk is removed. A portion of the milk is then heated to 45.degree. C. and conveyed to a sound velocity test cell. A second portion of the milk is heated to 65.degree. C. and conveyed to a second sound velocity test cell. The rate at which a sound pulse traverses the milk in each of the cells is determined by determining the frequency with which the pulses traverse the milk in each of the test cells. The resulting frequency is proportional to the velocity of sound through the milk. The frequency values are coupled to a computer wherein two simultaneous linear equations are solved to arrive at the percent fat and the percent solids-not-fat in the milk.