  We address the question of how to identify the QCD phase transition using
measured light (u,d,s-structured) hadrons, without invoking comparison to the
QCD $\epsilon_c$ predictions, and extract $\epsilon_c$ from the data. We
analyse several particle and nuclear collisions and extract their chemical
freeze-out temperature $T$ at zero baryochemical potential ($\mu_B$). We find
at $\mu_B=0$ a universal rise and saturation of both the $T$ and of the
strangeness suppression factor $\lambda_s$ (=$\frac {2\bar{s}} {\bar{u} +
\bar{d}} $) with increasing initial energy density ($\epsilon_i$). The onset of
saturation of both $T$ and $\lambda_s$, is interpreted as due to the event of
the QCD phase transition. The critical energy density is estimated to be
$\epsilon_c$ $\sim$ 1 +0.3 -0.5 GeV/fm$^3$, corresponding approximately to a
$\sqrt{s}$ of $\sim$ 8.8 GeV for central Pb+Pb collisions. Concerning the role
of strangeness, we identify trivial and non-trivial sources of strangeness
enhancement: The peak of $\lambda_s$ in Pb+Pb collisions at $\sqrt{s}$=8.8 GeV
and other phenomena of 'strangeness enhancement' defined with respect to p+p
data, are trivially traced back to the different baryochemical potentials and
$\epsilon_i$ of the compared systems. A non trivial redefined '$\lambda_s$
enhancement' is however also present. The netbaryonfree $\lambda_s$ limit is
estimated to be approximately reached in Au+Au collisions at the LHC.
