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Minimal fermentable sugar loss is essential for successful sugar beet processing, and storage of concentrated (thick) juice may improve economics by extending the processing campaign. However, an accurate, real time evaluation of juice quality is necessary, and reference chemical methods are time consuming and expensive. The objective of this study was to develop and validate near infrared spectroscopic (NIRS) calibration models for predicting quality of sugar beet thick juice used in bioethanol applications. Thick juice possessing varied refractometeric dry solids (60 to 70Brix) were stored across contrasting pH (2 to 11) for 24 wk at 21C. NIR spectra and reference chemistry values for brix, water activity (aw), pH, were collected at 2 wk intervals and carbohydrate concentrations were quantified at the beginning and conclusion of the 24 wk storage experiment. NIR spectra (535 samples) were collected with a diode array spectrometer, equipped with a syrup module. A partial-least squares calibration model with mean centered preprocessing and multiplicative signal correction provided the best models for thick juice evaluation. An RPD value > 4.8 suggests useful calibrations were obtained for brix across all pH ranges and for aw from samples stored under acidic storage conditions. The juice pH calibration were poor (RPD 2.1, 1.5) and additional sample data must be included to accurately assess the model performance of carbohydrate predictions.