Dry matter content in curd is adjusted by feeding starting product into a nozzle separator while determining a content of dry matter and/or protein, and measuring mass flow of the starting product. The nozzle separator separates the starting product into whey and curd fractions, which are separately discharged from the separator and the mass flow of the whey fraction is measured. Mass flow rate of supplied starting product is adjust based on the determined content of dry matter or protein of the starting product, measure mass flow of the starting product, and measured mass flow of the whey fraction. A determination of the dry matter content and/or the protein content of the curd fraction is carried out based on the determined mass flow of the starting product and the mass flow of the whey fraction and the determined dry matter content and/or protein content of the starting product.