The viscosity of skim milk concentrates increases during storage as result of interactions between milk proteins, minerals and other solids. The present study demonstrates how these interactions can be controlled by addition of calcium or glucono-δ-lactone. Milk concentrates, produced from reverse osmosis with 28% total solids, were heat-treated at 75 or 110 °C for 18 s, followed by addition of CaCl2 (0, 25 or 50 mm) and glucono-δ-lactone (0 or 80 mm), before storage at 5 °C for 20 days. Addition of CaCl2, glucono-δ-lactone or their combination were found to reduce the viscosity build-up during storage, but the extension depends on the intensity of heat-treatment and pH of the concentrates. The more pronounced effects were observed for concentrates heat-treated at 110 °C, which were also the more viscous concentrates. An increase of colloidal calcium reduce the partial specific volume of casein micelles leading to a less viscous milk matrix.