Sugarcane may be harvested mechanically or by hand, but must be transported to a processing plant immediately because sucrose decays very quickly. The sugarcane is cleaned and then is milled in two steps.
The canes are first broken using a combination of knives, shredders, crushers, and rollers. The canes are then ground using a series of roller mills. After each roller, water is run over the crushed sugarcane. The water run in the opposite direction that the sugarcane travels, beginning at the last mill, and ending at the first. This process, called imbibition, maximizes the amount of sucrose extracted from the sugarcane. The juice (water with the dissolve sucrose) is strained, and then clarified by heating it with a small amount of lime. The lime neutralizes the acids that are created as the juice is heated to around 200º F (95º C). Impurities precipitate out, and the remaining sucrose and water solution moves to the evaporator.
The juice first passes through a heat exchanger, and then through multiple effect evaporators. Pressure decreases at each evaporator, allowing the juice to boil at successively lower temperatures. The remaining syrup is approximately 65% sucrose and 35% water. The syrup is aerated, filtered, and clarified again before being sent to vacuum pans for crystallization.
The syrup is boiled to a level of super saturation and then seeded to catalyze crystal formation. When the volume of sugar crystals and liquor reach the maximum level, the mixture is sent to a centrifugal separator. The centrifuge separates the sugar crystals from the liquor left over. The liquor is returned to the vacuum pans and the process is repeated twice more. All of the crystals are washed, dried, cooled and sold as cane sugar. The liquor left over after the third centrifuging is sold as black strap molasses. Some of the black strap molasses is used as the seeding solution for crystal formation. (EPA)
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