Abstract: Milk to be standardized is fed continuously to a centrifugal separator which discharges separate flows of skim milk and cream; and the density of the separated cream is maintained substantially constant by continuously measuring such density and using these density measurements to control one of the separate flows. Pipelines leading from these separate flows to a mixing zone are provided with meters for measuring the flow rates of the skim milk and cream, respectively; and a quotient controller operatively connected to the flow meters controls the flow through one of the pipelines to maintain the quotient of the respective flow rates substantially constant.