The unit operation is often placed in a separate media preparation room/area (clean room area 1). Challenges are the sterile and most often mycoplasma free filtration and filling into a receiving bag. The media has to have a defined pH and Conductivity value. The media is prepared with different components which could have a low solubility or a high viscosity. Media components could be added solid (powder addition via mixing bags) or liquid (via 2D bags and titration line). The pH adjustment depends on the buffer strength, acid/base strengths-volume and titration line diameter. Therefore, scale down trials are recommended.