  We show that it is possible to isolate a set of kaon fluctuations in lattice
QCD. By means of the Hadron Resonance Gas (HRG) model, we calculate the actual
kaon second-to-first fluctuation ratio, which receives contribution from
primordial kaons and resonance decays, and show that it is very close to the
one obtained for primordial kaons in the Boltzmann approximation. The latter
only involves the strangeness and electric charge chemical potentials, which
are functions of $T$ and $\mu_B$ due to the experimental constraint on
strangeness and electric charge, and can therefore be calculated on the
lattice. This provides an unambiguous method to extract the kaon freeze-out
temperature, by comparing the lattice results to the experimental values for
the corresponding fluctuations.
