  The implications of a QCD phase transition at high temperatures and densities
for core-collapse supernovae are discussed. For a strong first order phase
transition to quark matter, various scenarios have been put forward in the
literature. Here, detailed numerical simulations including neutrino transport
are presented, where it is found that a second shock wave due to the QCD phase
transition emerges shortly after bounce. It is demonstrated that such a
supernova banging twice results in a second peak in the antineutrino spectrum.
This second peak is clearly detectable in present neutrino detectors for a
galactic supernova.
