Steady shear viscosity of ultrafiltered whole and skim milk retentates before and during fermentation

Steady shear viscosities are reported for skim and whole milk retentates of different volume concentrations after ultrafiltration, as well as during f ermentation for the most concentrated retentates with and without salt addi tion. Retentates up to 3X exhibit Newtonian behaviour, while the most conce ntrated retentates (5X and 5.3X whole and skim) fit the power law model. Th e fermentation follows a three-phase model, during which the pH decreases f rom the natural pH of 6.0-6.5 to around 5.0-5.1. The viscosities of the fer mented retentates vary significantly with the change of pH, depending on th e fat and salt contents.