The present invention relates to a process for production of a concentrate of skim milk or whey, comprising the steps of providing a feed of skim milk or whey, subjecting said feed to a reverse osmosis to obtain a reverse osmosis permeate and a concentrate of skim milk or whey, and subjecting the concentrate of skim milk or whey to an ultra-filtration to obtain an ultra-filtration permeate and a retentate of skim milk or whey. The present invention further relates to a system thereof.