a method for manufacturing plastic containers in which , for each container , a plastic preform containing air is supplied ; the preform is heated at a preform temperature over the glass temperature of the preform material , the preform is inserted in a mold having a mold cavity ; and the preform is expanded to a container having the shape of a mold cavity by a forming liquid . the method also includes , between steps and , the injecting of a gaseous product into the preform containing air , wherein the gaseous product is absorbable by the forming liquid . the injection conditions of the gaseous product are selected such that the injected gaseous product expels the air out of the preform .