The method involves guiding a treatment head (5) in an interior of a plastic beverage container (10) to be sterilized, where the treatment head is transmitted into the interior of the container during a predetermined time period of radiation. The container is moved against the head in a longitudinal direction (L) of the container during the predetermined time period with a relative motion speed (v), where the motion speed of the head is varied in the interior of the container during the predetermined time period and is controlled independent of an internal profile (10a) of the container. Independent claims are also included for the following: (1) a method for determining a travel profile for internally sterilizing a container (2) a device for sterilizing a container, comprising a treatment head.
