Refining Sugar

Sugar is a product that nobody needs but everyone wants, so it has been highly valued ever since 1788, when it was especially valuable in the form of rum. In the later nineteenth century, when cane sugar was grown in northern Australia and in Fiji, it was possible to extract sugar roughly from the molasses, but this sugar contained impurities. Sugar mills can produce raw sugar, which still contains some molasses, giving it more colour (and impurities) than the white sugar which is now consumed in households. As tastes changed, refining became vital. The Colonial Sugar Refining Company addressed this problem in the 1870s onwards, by building refineries in Pyrmont and elsewhere, and scouring Europe to recruit expert chemists and engineers.

Raw sugar (98% sucrose) must be refined (to 99.9%) to create crystalline white sugar and the other forms (syrup, treacle, molasses, tablet) in which sugar is sold. Water, ash, organic matter and other sugars are removed to purify the product and prevent its deterioration. These impurities are small but elusive: they require hot-water washing, adding and removing lime, carbon dioxide and bone charcoal, filtering, boiling in a near-vacuum, warm air drying and sieving.

In the traditional refining process, raw sugar was first mixed with heavy syrup and centrifuged to wash away the outer coating of the sugar crystals. The remaining sugar was then dissolved to make a syrup, which had to be clarified by adding, then removing, a variety of chemicals. Colours were then removed from the clarified syrup by filtration: the purified syrup was then concentrated and crystallised under vacuum to produce white refined sugar.

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