Heat induced whey protein (WP) aggregates functionalities have been found to strongly depend on aggregates size distribution. The latter is affected by the time/temperature/shear rate history, which affects theological properties. This work evaluates the potential of the focused beam reflectance measurement (FBRM), an in situ granulometric method, and of an in-house developed tube viscometer, to perform in situ characterization of a WP aggregation process. Potential of turbidity techniques to characterize the process was also explored by off-line measurements. Experiments were investigated with WP solutions of 6% beta-lactoglobulin added with different concentrations of CaCl2, and heated at three different holding temperatures. Aggregates mean size, viscosity and turbidity increase with holding temperatures and CaCl2 concentration as expected. A good correlation was found between viscosity data and aggregates mean sizes. The latter were also well correlated with turbidity at 900 nm. FBRM and tube viscometer are shown to be promising and valuable tools to perform in-line characterization of heat induced WP aggregation process. (C) 2012 Elsevier Ltd. All rights reserved.