QCD sum rules predict that the change of the strange quark condensate $$ in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from $\phi$ meson decays. Due to the expansion of hadron matter in heavy-ion collisions, the $\phi$ peak suffers a smearing governed by the interval of density in the expanding fireball, which appears as effective broadening of the di-electron spectrum in the $\phi$ region. The emerging broadening is sensitive to the in-medium change of $$. This allows to probe directly in-medium modifications of $$ via di-electron spectra in heavy-ion collisions at SIS energies with HADES.