A novel Sensor Reactor technology is presented which permits 1 3 C labeling experiments for metabolic flux analysis during large-scale, semi-industrial, (fed-) batch fermentation processes deriving a series of flux maps that document fermentation courses in detail. The small-scale Sensor Reactor can be inoculated within 1.50-1.20s via a special inoculation unit with an inoculation volume accuracy of 1.025+/-0.021L. The large-scale production reactor (here: 300L) and the Sensor Reactor were run in parallel master/slave modes to control the current pH, temperature, pressure and dissolved oxygen values as changing set points for the Sensor Reactor. Using an automated pulsing technology, glucose pulses of 5g/L could be realized within 0.51s. The similarity of fermentations in the Sensor Reactor with the production process was demonstrated by studying l-lysine production with C. glutamicum during multiple, 'simulated' labeling experiments each lasting 2.5h. 'Real' labeling experiments are presented in Part II.