Sugarcane can be harvested by way of hand cutting, machine cutting, or mechanical raking. Upon arriving at a mill, it is first cleaned of dirt and any extraneous material that may be present. It is then chopped or shredded to change the harvested material to a fibrous material ready for sugar extraction. Several mills consisting of 3 rollers are run in series, with hot water being added after the first crushing. This process squeezes out the sugar, and the plant material left over is known as bagasse (bə-găs).
Bagasse is often used as a biofuel at the mill. It has also been studied and applied as an alternate energy source (Dellepiane, 2003) It is burned in boilers that vary in air pollutant concentrations based on different operating procedures designed to manage start-up time and temperature regulation. The boilers are often designed to be somewhat inefficient to maximize the amount of bagasse burned in the process, minimizing the waste product requiring disposal. (Ogden, 1999) Bagasse has also been used for other purposes. One example would be as an adsorbent in water treatment processes. (Venkat, 2006)
After going through the rollers, the sugar is then treated by clarification of heat and the addition of lime. This serves two purposes: causing impurities to settle out and preventing the sugar from changing form (Sucrose is the form desired for crystallization.) After clarification, the sugar is boiled to evaporate out the water and concentrate the sugar into a heavy syrup ready for crystallization. The crystallization occurs by seeding and further boiling. The crystals are separated out of the remaining liquid, which is molasses.
The crystals are dried and stored and can then go on to a refining process.