Background and Objectives: Recognizing the impurities of sugar beet and also comparing different methods of juice purification have shown that the chemical purification based on lime and carbon dioxide is really efficient and economic in the sugar industry. Factories have to control and improve purification stages to achieve clear juice with high chemical purity, low color, minimum hardness, sufficient thermal resistance and with no insoluble solid matters in producing white sugar with high purity and efficiency. The aim of this study was to investigate the effects of alkalinity changes in preliming and liming stages on improving the color of thin and thick juices.

Materials and Methods: In the current study, changes in pre-liming alkalinity (0.2, 0.3 and 0.9) and liming alkalinity (1.3, 1.4, 1.5 and 1.6) (mg CaO/ 100 ml juice) during the operation were studied in Sharekrod sugar factory. According to the discharge and retention time of each stage (raw juice, thin juice, and thick juice), the samples were taken and the color changes were studied.

Results: The results showed that alkalinity changes of 0.4 in preliming along 1.4 in liming and 0.4 in preliming along 1.3 in liming (mg CaO/ 100  ml juice) caused imbalance of cation/anion, sucrose hydrolysis and invert sugar, and produced undesired color in the thin or thick juice. These changes also had undesired effects on the juice’s resistance. But 0.2 in preliming and 1.6 in liming as well as 0.3 in pre-liming and 1.6 in liming had positive effects. Therefore, a thin juice with pH of 8.9 and low color increase (20%) was produced.

Conclusions: According to the results, some of the enforced changes were more effective in purification process and improved it.