Method for processing animal skim milk

A process for preparing a first nutritional product and a second nutritional product, the process comprising:

• (a) microfiltering (MF) animal skim milk over a membrane having a porosity of 0.10-0.35 micrometer and at a volume concentration factor of 1.5-8, resulting in a retentate (MFR) and a permeate (MFP), wherein the protein fraction of the MFR comprises at least 85 wt. % casein and less than 15 wt. % whey protein;
• (b) ultrafiltering (UF) the MFP over a membrane having a molecular weight cut-off of at most 25 kDa at a volume concentration factor of 1.5-8, resulting in a retentate (UFR) and a permeate (UFP);
• (c1) combining part of the MFR and the UFR to obtain a composition having a casein/whey protein weight ratio of 20/80-70/30 to prepare the first nutritional product;
• (c2) using the remainder MFR to prepare the second nutritional product;
• wherein:
• the first nutritional product is an infant formula base product;
• and
• the second nutritional product is a growing-up milk for a child of 12-36 months of age;
• and
• the second nutritional product comprises less than 50 wt. % of protein from a different source than the protein comprised in the MFR.