Non-lead polarimetry for sugarcane juice and factory products

Polarimetry is used worldwide as a simple sucrose content measurement. This method needs a clarification step to remove sample turbidity for correct light transmittance on a polarimeter. The conventional clarification with lead acetate for polarimetric measurement at 589.44 nm was compared with a physical method utilizing a polarimetric measurement at 882.6 nm. Filtration with filter aids is a physical method which has less impact on the environment than lead. Comparison between polarimetry at 589 nm and 882.6 nm and sucrose content by chromatography for sugar factory products as mixed juice, bagasse, filter cake and molasses are presented. These products came from two sugar factories of Réunion Island: Le Gol factory (milling tandem) and Bois-Rouge factory (diffuser). Polarimetry at 882.6 nm gave lower contents compared to measurements at 589 nm for cane (–0.075 g/100 g), mixed juice (–0.07), A run-off syrup (–0.19), C massecuite (–1.67) and final molasses (–3.82) and higher results for filter cake (+0.06). There was no difference for bagasse. The method repeatability was 0.05 for mixed juice and 0.04 for molasses. Polarimetry at 882.6 nm has been used in sugar factories since 2005 and for cane payment in Réunion from the beginning of 2009 crushing season.