  We analyze the properties of four-quark condensates and scalar
susceptibilities in the meson gas, within finite temperature Chiral
Perturbation Theory (ChPT). The breaking of the factorization hypothesis does
not allow for a finite four-quark condensate and its use as an order parameter,
except in the chiral limit. This is rigorously obtained within ChPT and is
therefore a model-independent result. Factorization only holds formally in the
large $N_c$ limit and breaks up at finite temperature even in the chiral limit.
Nevertheless, the factorization breaking terms are precisely those needed to
yield a finite scalar susceptibility, deeply connected to chiral symmetry
restoration. Actually, we provide the full result for the SU(3) quark
condensate to NNLO in ChPT, thus extending previous results to include kaon and
eta interactions. This allows to check the effect of those corrections compared
to previous approaches and the uncertainties due to low-energy constants. We
provide a detailed analysis of scalar susceptibilities in the SU(3) meson gas,
including a comparison between the pure ChPT approach and the virial expansion,
where the unitarization of pion scattering is crucial to achieve a more
reliable prediction. Through the analysis of the interactions within this
approach, we have found that the role of the $\sigma$ resonance is largely
canceled with the scalar isospin two channel interaction, leaving the
$\rho(770)$ as the main contribution. Special attention is paid to the
evolution towards chiral restoration, as well as to the comparison with recent
lattice analysis.
