  Neutron stars offer the opportunity to study the behaviour of matter at
densities and temperatures inaccessible to terrestrial experiments.
Gravitational-wave observations of binary neutron star coalescences can
constrain the neutron-star equation of state before and after merger. After the
neutron star binary merges, hyperons can form in the remnant, changing the
behaviour of the neutron-star equation of state. In this study, we use
finite-entropy equations of state to show that a post-merger remnant can spin
up due to cooling. The magnitude of the spin-up depends on the neutron-star
equation of state. If hyperons are present, the post-merger spin-up changes the
peak gravitational-wave frequency by $\sim 540$ Hz, when the entropy per baryon
drops from $s=2$ $k_B$ to $s=0$ $k_B$. If hyperons are not present, the
post-merger spin-up changes by $\sim 360$ Hz, providing a gravitational-wave
signature for exotic matter. We expect the same qualitative behaviour whenever
temperature dependent phase transitions are triggered.
