  We have developed a phenomenological effective quantum-field theoretical
model describing the "hadron gas" of the lightest pseudoscalar mesons, scalar
{\sigma}-meson and {\sigma}-vacuum, i.e. the expectation value of the
{\sigma}-field, at finite temperatures. The corresponding thermodynamic
approach was formulated in terms of the generating functional derived from the
effective Lagrangian providing the basic thermodynamic information about the
"meson plasma + QCD condensate" system. This formalism enables us to study the
QCD transition from the hadron phase with direct implications for cosmological
evolution. Using the hypothesis about a positively-definite QCD vacuum
contribution stochastically produced in early universe, we show that the
universe could undergo a series of oscillations during the QCD epoch before
resuming unbounded expansion.
