A through-flow freezer is disclosed comprising a freezing cylinder, an inlet pipe, an inlet blocking device, an air inlet, an outlet pipe and an outlet blocking device, wherein, at least in one operational mode of the through-flow freezer, the inlet blocking device and the outlet blocking device are closed such that a certain amount of mix and a certain amount of air substantially corresponding to a desired overrun in the freezing cylinder can be entrapped in the freezing cylinder by introducing air via the air inlet. Furthermore, a method for starting up a through-flow freezer is disclosed comprising the step of adding air through the air inlet until a certain amount of mix and a certain amount of air substantially corresponding to a desired overrun is entrapped in the freezing cylinder and a certain cylinder pressure is reached in the freezing cylinder before starting the cooling of the freezing cylinder.