The invention relates to a bioreactor comprising a chamber for containing cells or tissue cultures within a culture medium. The bioreactor also comprises a detector capable of detecting a change in one or more metabolites associated with growth of the cell or tissue cultures within the chamber and a chamber drive capable of rotating the chamber at a first speed about a first axis and a second speed about a second axis, the second axis being disposed at an angle relative to the first axis. In use, the magnitude of the first speed and the second speed are independently variable of each other.