Whey proteins (WP) were replaced with rapeseed proteins (RP) at various protein mixing ratios at neutral pH and ionic strength of 150 mM. Protein gels were formed at 95 °C and another temperature of 80 °C, below the denaturation temperature of RP, to understand the importance of whether RP gelled or not for changes in rheological properties in mixed gels. Gels were analyzed for their microstructure, rheological responses (e.g. G’) and water holding (maximum amount of exuded water (Amax) and ease with which water can be exuded (k)). The rheological responses obtained for mixed gels was compared to the ones of the single systems at the corresponding concentrations to understand the importance of the rheological moduli of the single systems to the modulus of the mixed gel and to enable the quantification of synergistic stiffening (S = G΄mixture/(G΄WP + G΄RP)). For gels formed at 95 °C a broader window for synergistic stiffening was formed compared to gels formed at 80 °C. Synergistic stiffening occurred when gel coarseness decreased and/or when the differences between the moduli of the individual protein gels were minimized. Water holding properties of mixed gels were tailored due to changes in the gel microstructure or due to synergistic stiffening. The behavior of k as a function of protein mixing ratio in mixed gels was similar to the behavior of gel stiffness. The decrease of k correlated well with an increase in gel stiffness. Gel coarseness and gel stiffness were inextricably linked in regards to their importance for changes in Amax.