Mixed Juice Clarification Revisited

The clarification of mixed juice has been the subject of research for decades, due mostly to its large impact on sugar quality. Much, if not all, of the work has however been done on mixed juice originating from milling rather than from diffusion. This paper examines a back-to-basics, laboratory approach, involving cane juices produced from conditions simulating milling and diffusion. Furthermore, different types of cane, for example fresh versus deteriorated, clean stalks versus stalks plus tops and trash, have been used. Saccharate and milk of lime have also been compared. Analytical techniques were carefully considered and methods such as X-ray fluorescence were used, and material balances across clarification were done. The laboratory work shows that, for the same cane quality, clear juice quality in terms of phosphate, calcium, magnesium, silica and sulphated ash is the same whether milling or diffusion has been used. Saccharate liming always yields better clear juice in terms of turbidity, colour, phosphate and calcium contents. Material balances closed well across clarification, except for phosphate and for silica; this highlights the need for sampling/analytical improvements for these two species. Finally, the effect of clarifier mud carryover on sugar quality is discussed.