An installation for manufacturing containers by moulding from a perform includes at least one moulding unit having a control device for controlling at least one nozzle associated with a mould, the nozzle being vertically movably mounted so as to move vertically between a top position and a bottom position in which the mould is closed. The nozzle covers at least one flow opening that includes an upper horizontal wall of the mould. The manufacture involves at least a first step including, the mould being closed, systematically controlling the vertical descent of the nozzle towards the bottom position independently of the presence or absence of a preform in the mould so that, both when the installation is operating and when it is at rest, the internal volume of the mould is isolated in order to avoid the risk of airborne particulate contamination.