The initial stage involves sampling, weighing and washing the sugarcane. From there the material passes to can crushers and then into the mill. The bagasse, which results from the milling, is used in the boilers for steam production that is used to power the process. The surplus bagasse from this stage is used in industry.
Juice obtained from the mill is weighed in order to continue with the heating, clarifying and filtering process whereby those materials found in the juice, different to sucrose, are separated. Once the juice evaporates concentrated cane syrup is obtained which is taken to pans, where crystallization takes place. Subsequently the cooked mass is obtained, that then goes to a centrifuge, where the sugar is separated from the syrup.
Finally, the sugar is dried, cooled and packaged in its different forms, ready for sale
Harvesting
Sugar cane is harvested by chopping down the stems but leaving the roots so that it re-grows in time for the next crop. Harvest times tend to be during the dry season and the length of the harvest ranges from as little as 2 ½ months up to 11 months.
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 fibre 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 fibres and the green extracts from the plant are all mixed in with the sugar.
Clarification
The extracted cane juice is pH tested and adjusted with lime before it is heated and sent to large clarifying tanks. These tanks
allow for the settling of solids to the bottom leaving only clear juice to continue through the process.
Evaporation
The factory can clean up the juice quite easily with slaked lime (a relative of chalk) which settles out a lot of the dirt so that it can be sent back to the fields. Once this is done, the juice is thickened up into a syrup by boiling off the water using steam in a process called evaporation. Sometimes the syrup is cleaned up again but more often it just goes on to the crystal-making step without any more cleaning. The evaporation is undertaken in order to improve the energy efficiency of the factory.
Boiling
The syrup is placed into a very large pan for boiling. In the pan even more water is boiled off until conditions are right for sugar crystals to grow.
Crystallisation
The heated syrup begins to crystallize and separates into sugar crystals and molasses called “massecuite.” The crystallizers cool the mixture of sugar crystals and molasses which causes the crystals to grow in size.You may have done something like this at school but probably not with sugar because it is difficult to get the crystals to grow well. In the factory the workers usually have to throw in some sugar dust to initiate crystal formation.
Centrifugation
To remove the sugar crystals from the molasses, high-speed rotating centrifugals spin off the molasses leaving only the raw sugar crystals on the centrifugal screens. The remaining product is blackstrap molasses which is then stored in tanks and later sold as cattle feed. After all of the commercially recoverable raw sugar is produced it is transferred into huge warehouses for storage until It is ready to be transported to refineries.
Sugar processing is a highly specialized, computer-controlled, technical process that requires a combination of sensitive machinery and experienced individuals to succeed. Approximately one ton of sugarcane is required to produce 220 pounds of raw sugar. We at Sugar Cane Growers Cooperative of Florida are proud of our facilities and the people who run them.
Storage
The final raw sugar forms a sticky brown mountain in the store and looks rather like the soft brown sugar found in domestic kitchens. It could be used like that but usually it gets dirty in storage and has a distinctive taste which most people don’t want. That is why it is refined when it gets to the country where it will be used. Additionally, because one cannot get all the sugar out of the juice, there is a sweet by-product made: molasses. This is usually turned into a cattle food or is sent to a distillery where alcohol is made.
Power
So what happened to all that fibre from crushing the sugar cane? It is called “bagasse” in the industry. The factory needs electricity and steam to run, both of which are generated using this fibre.
The bagasse is burnt in large furnaces where a lot of heat is given out which can be used in turn to boil water and make high pressure steam. The steam is then used to drive a turbine in order to make electricity and create low pressure steam for the sugar making process. This is the same process that makes most of our electricity but there are several important differences.
When a large power station produces electricity it burns a fossil fuel [once used, a fuel that cannot be replaced] which contaminates the atmosphere and the station has to dump a lot of low grade heat. All this contributes to global warming. In the cane sugar factory the bagasse fuel is renewable and the gases it produces, essentially CO2, are more than used up by the new cane growing. Add to that the factory use of low grade heat [a system called co-generation] and one can see that a well run cane sugar estate is environmentally friendly.
