A frozen beverage device to convert a liquid beverage into a semi-frozen or frozen form has inner and outer walls forming a refrigerant cavity containing a refrigerant material with a freezing point below the freezing point of the liquid, the refrigerant material occupying at least 80% of the volume of the refrigerant cavity. The outer wall has a base portion which can be moved from a first position, where the liquid is at least semi-frozen, to a second position where the internal pressure in the refrigerant cavity urges the inner wall outwardly towards the outer wall so that the refrigerant material contacts a maximum area of the surface of the inner wall in the refrigerant cavity for maximum heat transfer and to minimise constriction of access to the frozen beverage. Alternative methods to seal the inner and outer walls to close the refrigerant cavity are also disclosed.
