Lets assume that we can produce a quark-gluon plasma and then we try to cool it down, what will happen to it ?
You get the quark-anti quark (meson) and triple quark baryon (or triple antiquark i.e. anti-baryon) bound states (where the quarks/anti-quarks interact with gluons).
At a collider experiment, there is no need to "actively cool" the quark gluon plasma, this happens automatically and one sees the hadrons (mesons/baryons/anti-baryons) in the detector.
In the evolution of the early universe, this is what started the "hadron epoch".