AbstractL/A controllers have extended their use from continuous to fed‐batch fermentation where the control is applied from the start of an initial batch phase. As opposed to proportional integral derivative (PID) controllers where even a startup procedure is recommended prior to fed‐batch, the L/A controller is not upset by an early connection. It is easily retuned continuously by means of ethanol measurements and can cope with a large range of output conditions. The performance of an L/A algorithm, which uses biomass concentration as the controlled variable, is assessed through simulation. The self‐contained algorithm is relatively simple with no greater intrinsic complexity than modern PID stand alone controllers.