New long-term storage techniques are necessary to preserve fermentable sugars from sugar beet (Beta vulgaris L.) varieties which may qualify as advanced biofuel feedstocks in the United States. The focus of this study was to evaluate the combined effect of pH and refractometric dissolved solids (RDS) content on fermentable sugar preservation in raw thick beet juice stored for 24 wk at 23 +/- 1 degrees C. Response surface methodology was applied to model the change in fermentable sugars in raw thick juice stored under controlled acidic (2 <= pH <= 5) and alkaline (8 <= pH <= 11) conditions in combination with RDS weight fractions in the range of 60-69%. Combinations of pH <= 3.5 or pH >= 9.5 with RDS >= 64.5% were effective in preserving up to 99% of fermentable sugars in stored raw thick juice. Following storage, yeast fermentation of acidic treatments achieved efficiencies of up to 82% relative to raw juice, whereas yeast fermentation was hindered in alkaline treatments resulting in efficiencies of up to 54%. (C) 2013 Elsevier Ltd. All rights reserved.