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How Sucrose Is Extracted from Sugarcane

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How Sucrose Is Extracted from Sugarcane

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  • August 2011
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Extraction
The first stage of processing is the extraction of the cane juice. In many factories the cane is crushed in a series of large roller mills: similar to a mangle [wringer] which was used to squeeze the water out of clean washing a century ago. The sweet juice comes gushing out and the cane fiber is carried away for use in the boilers. In other factories a diffuser is used as is described for beet sugar manufacture. Either way the juice is pretty dirty: the soil from the fields, some small fibers and the green extracts from the plant are all mixed in with the sugar. There are several important aspects to extraction which involve the energy balance of the factory, the efficiency of extraction and therefore ultimately the profitability of operations: •The manager needs to process the cane as soon as possible if sugar losses are to be avoided it needs to have a sufficient supply in storage for times when cutting and transport are stopped, whether deliberately or not. Typically, cane is processed within 24 hours of cutting; •Cane preparation is critical to good sugar extraction, particularly with diffusion extraction. This is achieved with rotating knives and sometimes hammer mills called "shredders". However shredding requires extra energy and more equipment; •The extraction is actually conducted as a counter-current process using fresh hot water at one end being pumped in the opposite direction to the cane. The more water that is used, the more sugar is extracted but the more dilute the mixed juice is and hence the more energy that is required to evaporate the juice; •The more accurately that the mills are set [adjusted], the drier is the residual fiber and hence the less sugar remaining in the fiber; •A typical mixed juice from extraction will contain perhaps 15% sugar and the residual fiber, called bagasse, will contain 1 to 2% sugar, about 50% moisture and some of the sand and grit from the field as "ash". A typical cane might contain 12 to 14%...

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