Fourier-transform infrared (FTIR) spectroscopy was used to monitor amino acids, organic acids, and changes during ripening. Twelve Cheddar cheese samples were ripened for 73 days and samples were drawn periodically. Water-soluble fractions of samples were analyzed by gas chromatography (20 amino acids), liquid chromatography (three organic acids), and FTIR spectroscopy (4000-700 cm-1). Spectra were correlated with chromatographic data and ripening events and analyzed by multivariate statistics to develop prediction and classification models. Most models showed a good fit (correlation coefficient ≥0.89) and could predict the levels of amino acids and organic acids and age of the cheese in less than 20 min. Lactic acid, leucine, glutamic acid, asparagine, phenylalanine, and valine were present in significantly high concentrations. Samples could be classified based on their age due to the differences in spectral region 1800-900 cm-1. Some of the changes in the FTIR spectra of WSF during ripening were also characterized. © 2011 Elsevier Ltd.