The installation (1) comprises: a vacuum expansion chamber (4), having an inlet (4a) provided with a first gas- tight valve device (5) for receiving a flow of semi-finished pieces (3) prepared starting from a confectionery compound and including particles, such as air bubbles and/or powders, capable of causing an expansion thereof under vacuum, and an outlet (4b). In chamber (4) there is provided a rotating drum (7) having a grille structure, intended to receive and transfer to the outlet (4b) of said chamber (4) a flow of said semi-finished pieces (3), in a controlled period of time sufficient to allow an expansion thereof under vacuum. A cooling and conveying apparatus (10) under vacuum, at a controlled temperature, has an inlet coupled with the outlet of the expansion chamber (4), and an outlet having an associated second gas-tight valve device (18) for discharging the expanded and cooled confectionery products (3). This apparatus (10) includes at least one cooling and conveying unit (11-14) comprising a conduit under vacuum (11 a- 14a) in which there is provided a worm conveyor device (11d-14d; 11e-14e) including a flexible spiral screw (11e-14e) intended to cause a displacement of the expanded pieces (3) at a controlled speed.