Heteroprotein complex coacervation (HPCC) refers to associative liquid-liquid phase separation occurring between two or more proteins. HPCC is primarily driven by electrostatic interaction (enthalpic contribution) and counterions release (entropic contribution). Its physicochemical properties, largely influenced by electrostatic interaction strength, can be modulated via pH and ionic strength. A promising yet underexplored approach to tuning coacervation is altering solvent quality, specifically the dielectric constant (ε) of the medium [1]. Electrostatic interactions between a single cation and anion is described by the Coulomb energy (E=-e^2 \/4 πε_0 ε σ) where e is the elementary charge of the ions, σ is the separation distance between the ions, and ε_0 is the dielectric permittivity of a vacuum. β-lactoglobulin (βLG) and lactoferrin (LF) are known to form complex coacervates [2]. Here, we investigated HPCC between these two globular whey proteins in water/glycerol mixtures. The linear viscoelasticity of βLG/LF coacervates, prepared at pH 5.6, was examined as a function of temperature (T = 5–40°C) and glycerol content (0-40%). The thermal behavior was investigated using differential scanning calorimetry (DSC). Results showed a significant increase in the storage (G′) and loss (G′′) moduli with increasing glycerol content. The time-temperature superposition (TTS) principle applied to all βLG/LF coacervate systems, and TTS data were fitted to the Fractional Maxwell model. Activation energies (E_a), calculated using the Arrhenius equation, increased with glycerol content, indicating strengthening of the electrostatic interactions since E_a represents the activation barrier that needs to be overcome to dissociate an ionic pair within βLG/LF coacervates. DSC further revealed a freezing point shift to negative temperatures as a function of glycerol content. This study demonstrates that solvent quality can effectively tune the rheological and thermal properties of HPCC, offering potential for diverse applications.