At finite(=nonzero) temperature the situation is completely different. The particles interact with the thermal bath that surrounds them and this situation is reflected in the potential which now acquires extra terms. Addition of these terms results in a new quantity which is called the effective potential. At temperatures high enough the degenerate minima disappear and the potential becomes symmetric again. We say that the symmetry is restored and we deal then with a phase transition from a state with broken symmetry to a symmetric phase.
A powerful method in approaching questions like the restoration of spontaneously broken symmetries is to construct order parameters, which characterize the state of symmetry of the system under consideration. These quantities are zero in the one phase but not in the other. A classic example of an order parameter is the magnetization of a ferromagnetic substance, it is non-zero below the Curie temperature, but it disappears at temperatures higher than that. The system undergoes a transition from an asymmetric, ordered state with non zero magnetization at low temperature to a symmetric disordered state with zero magnetization at high temperatures well above the Curie point.
In QCD a convenient order parameter is the quark condensate. This quantity can be thought as a state of quark-antiquark pairs condensed into the same quantum mechanical state. They fill the lowest energy state -the vacuum of QCD- and in this sense the chiral symmetry is broken, since there is no invariance under chiral transformations. We expect that if we raise the temperature the quark condensate will disappear and the theory will be chirally symmetric. It is called the chiral phase transition.