Understanding the effect of evaporative concentration on casein micelle composition is of high importance
for milk processing. Alterations to the hydration, composition and size of casein micelles were
investigated in skimmed milk evaporated to concentrations of 12–45% total solids content. The size of
casein micelles was determined by dynamic light scattering, and the water content and composition
determined by analysis of supernatants and pellets obtained by ultracentrifugation. The mass balance
and hydration results showed that during the evaporation process, while micelles were dehydrated,
water was removed preferentially from the serum. The amount of soluble casein and calcium in the
serum decreased as a function of increasing solids content, indicating a shift of these components to
the micelles. The formation of a small proportion of micelle aggregates at high concentrations appeared
dependent on the time kept at these concentrations. Upon redilution with water, casein micelles were
immediately rehydrated and aggregates were broken up in a matter of minutes. Soluble calcium and
pH returned to their original state over a number of hours; however, only a small percentage of original
soluble casein returned to the serum over the 5 h period investigated. These results showed that casein
micelles are significantly affected by evaporative concentration and that the alterations are not completely
and rapidly reversible