Abstract: In a milk processing system wherein heat treated milk is initially separated into high-fat and low-fat milk and subsequently reconstituted by adding a selected proportion of high-fat milk to the low-fat milk, control means are provided for automatically controlling the proportion of high-fat milk mixed with the low-fat milk to provide a milk blend of standardized butterfat content which is then homogenized. The control means includes a photoelectric monitoring system for continuously measuring the butterfat content of a sample of the homogenized milk as the latter flows continuously through the processing system under pressure of the homogenizer in the system. The butterfat content measurement is converted to digital signals which are compared to a pre-set digital signal corresponding to a desired butterfat content level to produce a digital corrective signal which controls a digital valve regulating the proportion of high-fat milk blended with the low-fat milk in the processing system.