Harvesting Sugar Cane
The manual harvest process often begins with the sugar cane fields being burnt. 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.
The alternative way to harvest sugar cane – the mechanised harvest – involves a machine extracting the cane as it travels across the field, whilst loading it into a truck. Mechanised harvesting is seen as the future of cane harvesting. This is primarily because it is not only better for the environment and wildlife, but it is a more efficient operation taking the cane to the mill. Mechanised harvesting reduces the time of an average harvest by up to three-quarters, from 24-36 hours to only 6-12 hours. This increase in efficiency for the harvest means higher sucrose yields and larger profits for the plantations.
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, and also the quality of the cane. This has a direct impact on the price it will be sold for.
How to process sugar cane
At a sugar mill or facility, sugar cane undergoes the first of two possible stages of processing. The end result is raw sugar, which is pure sugar with some molasses content remaining. Molasses is a by-product of sugar, and is what gives raw sugar its brown appearance. Sugar cane processing at a mill requires a few stages to get sugar from sugar cane, and we will go through in them more detail below:
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.
After 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.
To avoid sucrose decomposition, the juice then passes through a process of pH correction. Once this has been done, the juice is mainly water, mineral salts and sugars.
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 placed 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 cane sugar is not food grade.
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Harvesting Sugar Cane
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