Bioprocess optimization is often limited by its inability to measure biomass, nutrients and product concentrations in a time frame that allows process adjustments. Infrared spectroscopic techniques can potentially be used to measure each of these components within about 3 min of sampling, of an unprocessed whole broth sample. In the present study, the use of Fourier transform mid infrared (FT-MIR), near infrared red (NIR), and Fourier transform (FT)-Raman spectroscopic techniques for at-line (rapid off-line) monitoring of biomass, glucose, and lactic acid in a lactic acid fermentation by Lactobacillus casei was investigated. Suitable spectral wavenumber regions were selected for principal least square (PLS) regression and principal component regression (PCR) and calibration models were developed. The standard error of calibration for the PLS-1st derivative calibration models for glucose, lactic acid, and optical cell density were 2.5, 0.7 g/l, and 0.23, respectively. Prediction errors were high for NIR and FT-Raman methods. Results indicated that FT-MIR spectroscopy could be used for rapid detection of glucose, lactic acid, and optical cell density during lactic acid fermentation.