Sugar Processing: Milling & Refining
Queensland's 23 sugar mills are in close proximity to the farms which supply them with cane. The mills operate during the harvesting and crushing season which extends from June to December. Raw sugar produced by these mills is stored at bulk sugar terminals before being sold to Australian and overseas refineries. The exception is the new Tableland mill whose syrup is transported to the company's coastal mills, Babinda, Mourilyan and South Johnstone, where raw sugar is then made.
To avoid deterioration in the sugar content levels, sugar cane is delivered to the mill with minimal delay after harvesting. This has led to the development of an extensive transport system which allows harvested cane to be moved quickly and efficiently to sugar mills by either road or rail. Queensland mills own and operate approximately 4,000 kilometres of narrow gauge railway.
At the mill, the sugar cane is crushed by large rollers. The extracted juice is then clarified to remove soil and impurities. This juice is concentrated into a syrup by boiling off excess water, seeded with raw sugar crystals in a vacuum pan and boiled until sugar crystals have formed and grown. The boiled mixture is centrifuged to separate the molasses from the crystals, which are tumble dried and placed in large storage bins for transport to bulk sugar terminals or refineries.
Recent technological advances in milling procedures and mill equipment have contributed to the efficiency and high quality of Queensland's raw sugar industry.
Most raw sugar requires further processing at refineries in order to meet food manufacturers and consumers needs.
The main products from Australia's refineries are white crystal sugars, brown sugars, liquid sugar, golden syrup and treacle.
At the refinery, the raw sugar crystals are washed and dissolved in hot water to form a syrup. Phosphoric acid and lime are added to the melted sugar to remove any impurities in the clarification process. The syrup is pressure filtered through cloth, passed through decolourising columns containing activated carbon, boiled in a vacuum pan and seeded with fine sugar crystals. When the crystals are large enough, they are discharged from the pan, centrifuged to remove excess liquid and then tumble dried. The dried sugar is then graded into required sizes prior to packaging and supply to customers.