A partial least-squares calibration model, relating mid-IR spectral features with fructose, ethanol, acetate, gluconacetan, phosphate and ammonium concns. has been designed to monitor and control cultivations of Gluconacetobacter xylinus and prodn. of gluconacetan, a food grade exopolysaccharide (EPS). Only synthetic solns. contg. a mixt. of the major components of culture media have been used to calibrate the spectrometer. A factorial design has been applied to det. the compn. and concn. in the calibration matrix. This approach guarantees a complete and intelligent scan of the calibration space using only 55 stds. This calibration model allowed std. errors of validation (SEV) for fructose, ethanol, acetate, gluconacetan, ammonium and phosphate concns. of 1.16 g/l, 0.36 g/l, 0.22 g/l, 1.54 g/l, 0.24 g/l and 0.18 g/l, resp. With G. xylinus, ethanol is directly oxidized to acetate, which is subsequently metabolized to form biomass. However, residual ethanol in the culture medium prevents bacterial growth. Online spectroscopic data were implemented in a closed-loop control strategy for fed-batch fermn. Acetate concn. was controlled at a const. value by feeding ethanol into the bioreactor. The designed fed-batch process allowed biomass prodn. on ethanol. This was not possible in a batch process due to ethanol inhibition of bacterial growth. In this way, the productivity of gluconacetan was increased from 1.8 * 10-3 [C-mol/C-mol substrate/h] in the batch process to 2.9 * 10-3 [C-mol/C-mol substrate/h] in the fed-batch process described in this study. [on SciFinder (R)]