Sugar cane is grown in warm to tropical areas of the world, with Brazil, India, Thailand, China and Australia as the leading producers. Each sugar cane plantation has multiple fields – all at different stages of cane production to ensure that there is always cane available to supply the mill. From planting the cane through to harvest, the process can take up to 18 months. Preparation of the cane ahead of it being planted is vital. The leaves are removed from the cane and then cut into 20cm tranches. The field row is then prepared with incisions made in the field at approximately 15-20cm in width. The cane is then placed inside the hole horizontally and left to grow.
Sugar Cane takes approximately 12-18 months to mature. During this time, it is important that the cane is treated with pesticides and fertiliser to enable a healthy and high yielding sugar cane. Cane sugar does not need to be re-planted, as only the top of the plant is removed during harvest. There are two ways that sugar cane can be harvested – manually and mechanised.
The manual harvest process begins with the sugar cane fields being torched. This removes all the leaves so that the cane can then be manually chopped to the ground by a team of farmers. However, this process takes days and the burning of the cane leaves results in wildlife and a reduction in the quality of the sucrose in the cane. Once the cane has been manually harvested, it is put on a truck by hand and driven to the mill.
Once the sugar cane is transported to the mill, it has to be weighed and examined to confirm how much cane has been delivered and to determine the TRS (Total Recoverable Sugar) content of the cane. The TRS content grades the quality of the cane – therefore it has a direct impact on the price paid for it, and the amount it will be sold for.
Once the cane has been graded, it is washed to remove any impurities ahead of being processed. The cleaning of the cane can be done wet or dry. Dry cleaning is the preferred method as it is more environmentally friendly and does not affect the TRS content.
Once the cane has been dried, it is chopped before it is crushed in big roller mills. This process removes the sugar cane juice. The juice is the valuable extract as it is used for sugar and ethanol production. The sugar cane waste, which is known as ‘bagasse’, is then used as fuel to generate electricity in the power plant.
The sugar cane juice is then sent for clarification. The juice is treated for precipitate elimination via coagulation and sedimentation. The process removes sand, clay and other substances from the juice. Nearly 90% of the weight of sugar cane is juice, which contains up to 17% of sucrose (common sugar) and small amounts of dextrose and fructose.The juice goes through a boiling process, where moisture is boiled off. During the boiling and evaporation process around 75% of the water is removed, resulting in a thicker syrup concentrate.The syrup is then cooked so that crystallisation and recuperation of the sucrose can take place.
The syrup is places in large vessels where it is rotated slowly, allowing it to cool evenly. Seeding is then carried out, where small seed crystals are added to the syrup to catalyse the crystallisation process. The molasses separates from the crystals, and the liquid is ready for the next stage.To complete the process, centrifuging then takes place. During this process the crystallised syrup is separated from the sugar and dried by being put into centrifuges. This produces raw sugar by separating the sugar crystals from the surrounding molasses.
For every 100 tonnes of cane that is processed, about 12 tonnes of VHP (Very High Polarity) sugar is produced and 4 tonnes of molasses.
The amount of molasses, which is leftover solution from the sugar processing, that is left on the crystals or added back to the sugar crystals determines what type of sugar is produced.
In addition to white granulated sugar, there are light and dark brown sugars that have a higher molasses content and are often produced for speciality use. Typically at this stage, the sugar is not food grade.Once the sugar has been produced, it is then ready to leave the mill to go to a sugar refinery for further purification, or to a terminal or port, to be delivered directly to an industrial client for use in its raw form.
