A method of separating a liquid mixture in a centrifugal separator, wherein the centrifugal separator comprises a centrifuge bowl arranged to rotate around an axis of rotation and in which the separation of a liquid mixture takes place, a frame which delimits a surrounding space that is sealed relative the surroundings of the frame and in which said centrifuge bowl is arranged, a drive member configured to rotate the centrifuge bowl in relation to the frame around the axis of rotation, wherein the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated, at least one liquid outlet for discharging a separated liquid phase and a sludge outlet for discharging a separated sludge phase to the surrounding space, a vessel connected to the surrounding space and arranged for collecting the separated sludge phase discharged from the centrifuge bowl, wherein the method comprises the steps of a) supplying a liquid feed mixture to be separated to the inlet of the centrifuge bowl, b) separating the liquid feed mixture into at least one separated liquid phase and a separated sludge phase, c) removing gas from the surrounding space to obtain a sub-atmospheric pressure in the surrounding space, d) discharging a separated sludge phase to said surrounding space, e) collecting said sludge phase in said vessel, f) removing said sludge phase from said vessel, g) spraying liquid into said vessel after step f) to reduce the level of foam present in said vessel. a centrifuge bowl arranged to rotate around an axis of rotation and in which the separation of a liquid mixture takes place, a frame which delimits a surrounding space that is sealed relative the surroundings of the frame and in which said centrifuge bowl is arranged, a drive member configured to rotate the centrifuge bowl in relation to the frame around the axis of rotation, wherein the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated, at least one liquid outlet for discharging a separated liquid phase and a sludge outlet for discharging a separated sludge phase to the surrounding space, a vessel connected to the surrounding space and arranged for collecting the separated sludge phase discharged from the centrifuge bowl, wherein the method comprises the steps of a) supplying a liquid feed mixture to be separated to the inlet of the centrifuge bowl, b) separating the liquid feed mixture into at least one separated liquid phase and a separated sludge phase, c) removing gas from the surrounding space to obtain a sub-atmospheric pressure in the surrounding space, d) discharging a separated sludge phase to said surrounding space, e) collecting said sludge phase in said vessel, f) removing said sludge phase from said vessel, g) spraying liquid into said vessel after step f) to reduce the level of foam present in said vessel. a) supplying a liquid feed mixture to be separated to the inlet of the centrifuge bowl, b) separating the liquid feed mixture into at least one separated liquid phase and a separated sludge phase, c) removing gas from the surrounding space to obtain a sub-atmospheric pressure in the surrounding space, d) discharging a separated sludge phase to said surrounding space, e) collecting said sludge phase in said vessel, f) removing said sludge phase from said vessel, g) spraying liquid into said vessel after step f) to reduce the level of foam present in said vessel.