Currently, the design of microemulsions is focussed on the formulation of environmentally compatible systems formed by non-harmful amphiphiles and oils. The use of sugar-based surfactants allows the design of microemulsions where, instead of the temperature, the addition of short- or medium-chain alcohols tunes the curvature of the amphiphilic interface. In this work, the resulting temperature stability of a sugar surfactant and rapeseed methyl ester based bicontinuous microemulsion is exploited to study the influence of temperature variations on the bending elastic constant κ. Quasi-elastic scattering of light and neutrons is used to separate long-range collective motions and local thermally excited undulations of the interface. κ in units of kT is found to be independent of temperature over a wide range.