The inhibition of the aggregation processes in proteins is currently a subject of great interest in many research fields, from the study of protein-misfolding related diseases to pharmaceutics, biotechnology and food science. αs1-casein, one of the four types of caseins, which are the largest protein component of bovine milk, has been found to hinder the aggregation process of several proteins, including the amyloid β-peptide, involved in Alzheimer's disease. To shed light into the mechanisms by which casein exerts this chaperon-like protective action, we studied its effect on the different steps of the aggregation process of Concanavalin A, by means of both static and dynamic light scattering, Thioflavin T fluorescence, Circular Dichroism and Atomic Force Microscopy. Our results show that casein has a poor effect on the first step of the process which leads to the formation of amyloid-like structures. On the contrary, it has a marked effect on the second step of the process, ascribable to clusters condensation and compaction, up to the formation of very large aggregates. Such an effect requires a larger molar ratio of casein with respect to what observed for the amyloid β-peptide, thus suggesting different mechanisms of interaction of casein, depending on both conformational properties and relative size of the aggregating molecules.