Processes and systems for pasteurizing and sterilizing a plurality of articles in a microwave heating system are provided. In certain aspects, groups of articles may be passed by a microwave launcher in a first convey direction and a second, opposite convey direction, so that each group of articles passes the microwave launcher more than once. Processes and systems described herein are also configured to uniformly heat spaced apart groups of articles without disrupting the operation of the microwave generator or distribution system.
