the invention relates to a method for applying capsules to a plastic container which is aseptically filled with a liquid and which is weld - sealed with a membrane . the capsule to be applied , which preferably is constituted of two aluminum foils having a collar , is placed on the membrane with a planar surface thereof and the collar is mechanically bent so that it is reliably secured to the container neck . the cap is then pressed onto it so that the collar is retained between the container neck and the cap in a form - and in a force - locking connection . the method according to the invention avoids the risk of the capsule being destroyed , which can happen during welding , and the risk of soiling , which can happen during gluing .