The invention relates to a method and an apparatus for controlling the quality in the manufacture of composite material which contains fiber based and polymer based material, wherein the manufacture includes a mixing process (1) to form agglomerates from a raw stock mixture. According to the invention, a combination of variables in the mixing process is observed, wherein the variables are selected from the group of moment, current consumption, time, sound, temperature and their combinations, and the mixing process as well as the quality of the agglomerates to be formed is controlled based on the acquired observations (6, 7).