New insights on the hard-to-boil massecuite phenomenon in raw sugar manufacture

Louisiana hard-to-boil (HTB) massecuites (mixtures of sucrose crystals in molasses) with markedly low heat transfer properties are a sporadic problem in sugarcane factories, which cause raw sugar and molasses production to decrease and increase, respectively. This usually occurs after severely deteriorated sugarcane has been processed, but the specific cause is unknown and only limited correction has been achievable. At the end of the 2006 sugarcane processing season, HTB and normal massecuites and molasses were collected from four Louisiana factories. Compared to normal samples, the HTB samples had 9.1–33.2% lower heat conductivity and 10.0–49.2% higher heat resistivity. The more HTB a sample is, the greater the increase in heat resistivity compared to the corresponding decrease in heat conductivity. Excess lime addition to neutralise acids during juice clarification is not the direct cause of hard boiling. Oscillatory deformation rheology applied at 20 °C to normal molasses samples gave typical mechanical spectra of concentrated solutions. In contrast, a highly viscous, intermolecular (gel) network was present in the HTB molasses, which would explain the difficulty of removing entrapped water on boiling. Polysaccharides in the samples were characterised. GFC, TLC, and methylation analyses suggested the presence of an arabinogalactan and endo-dextranase-resistant dextran structures. The HTB phenomenon may have different causes and mannitol is a contributing factor.