A method for producing a composite structure comprising fiber reinforced material by means of vacuum assisted resin transfer molding is described. The fiber material is impregnated with liquid resin, and the method comprising the steps of: a) providing a forming structure comprising a rigid mold part and a second mold part, b) placing the fiber material in the rigid mold part, c) sealing the second mold part against the rigid mold part to form a mold cavity, d) connecting a source of uncured fluid resin to at least one resin inlet communicating with the mold cavity, e) connecting at least one vacuum outlet communicating with the mold cavity, f) evacuating the interior of the forming structure through the at least one vacuum outlet, g) supplying uncured resin from the source of uncured resin to the mold cavity through the at least one resin inlet so as to fill the mold cavity with resin, and h) curing the resin in order to form the composite structure. During the evacuation process of step f), an airflow level through the at least one vacuum outlet is measured.