Regular and ultrafiltered (UF; 1Ã—, 2Ã— and 4Ã— concentrated) skim milk samples were treated with a range of enzymes including calf rennet, ficin and papain. The clotting properties, curd casein profiles and free amino acid (FAA) contents were determined. In general, UF milk samples coagulated faster and formed firmer curds irrespective of protein concentration. Furthermore, both ficin and papain had a more significant effect on proteolysis in curd formed from regular and 1Ã— UF milk than on 2Ã— or 4Ã— UF milk. Cardoon extract and calf rennet had very similar clotting properties, although the former caused both the capillary electrophoresis profile of caseins and FAA measurements to show slightly more extensive hydrolysis in the curd. The results suggest that the UF process may cause structural changes to proteins or other milk constituents with a resultant change in clotting properties and proteolysis of the casein molecules.