Microparticulated whey protein (MWP) is a fat replacer; manu- factured from whey protein concentrate in a process that primarily involves simultaneous heating and shearing. Alternative processes may be utilized instead, such as extrusion cooking at acid pH or dynamic high pressure shearing, i.e., micro-fluidization. The result is whey protein aggregates with particle sizes that usually range between 0.1 and 10 mm (Spiegel & Huss, 2002) and that have previously shown their ability to provide sensory sensations associated with the presence of milk fat, i.e., creaminess, when incorporated into low-fat stirred yoghurt. Regarding the rheological charac- teristics of yoghurts when MWP is included in the formulation, improvements of the texture in reduced fat set-style yoghurts have been reported. Whether these microparticles act as active or inert fillers in the yoghurt network has not been completely elucidated. Based on microstruc- tural studies, several authors have suggested that they do not interact actively with the casein micelles and other whey proteins, as homogenized fat globules do in full fat yoghurt.