A type of bioreactor in which microorganisms are cultured in such a way as to overcome growth limitation due to the initial substrate concentration. The substrate is therefore added to the growing cell culture either on a step-wise or continuous basis. A constant flow of substrate can be used to maintain a steady growth rate or exponential growth. Alternatively, the addition can be adjusted to maintain a constant substrate concentration but requires good and rapid measurement of the substrate in the medium.

A substrate-limited fed batch bioreactor uses a continuously supplied substrate with a low concentration. The required amount of substrate supplied can be checked periodically by stopping the supply and monitoring the effect on dissolved oxygen concentration.