An aerosol-generating system may include a liquid storage portion, a vaporizer, and a pump. The liquid storage portion may be configured to store a liquid aerosol-forming substrate. The vaporizer may be configured to volatilize the liquid aerosol-forming substrate. The pump may be configured to pump air into the liquid storage portion so as to push out a volume of the liquid aerosol-forming substrate from the liquid storage portion and to supply the volume of the liquid aerosol-forming substrate to the vaporizer. A method for generating an aerosol may be performed with the system.