Abstract: An aerator in which air is forced into the liquid by means of a helical rib surrounding a cylindrical member which is rotated in such a direction that air trapped beneath the helical rib is forced downwardly into the liquid. A diffuser at the bottom of the helical rib is effective to break up the trapped air bubbles into finer bubbles which are dispersed through and retained by the liquid. The cylindrical member on which the helical rib is disposed may be rotated by an electric motor which may be disposed either above the water line or beneath the water line at the bottom of the helical rib. Where necessary, air may be pumped into the space above the water so as to facilitate the introduction of air about the helical rib. Where the aerator is to be used with a container of limited size, the aerator may be either mounted on the cover of the container or may have associated therewith a closure member adapted to fit into the neck of such a container.