SUCROSE FROM SUGARCANE
After harvesting, the thick stems of the sugarcane are stripped of leaves. In the sugar factory the stems are crushed and shredded between toothed rollers. The juice of the crushed stems is extracted in mills consisting mainly of a system of rollers, often 9 or 12 in number, through which the shredded material passes.
This process is called grinding. During grinding, hot water is sprayed over the crushed material to dissolve out some of the remaining sugar. The solid, pulpy material remaining after extraction of the juice is known as bagasse; it is dried and used as fuel.
Lime is added to the raw juice drawn from the mill and the mixture is heated to boiling; during this heating, unwanted organic acids form insoluble compounds with the lime, which can be filtered off along with other solid impurities. Often the juice is treated with gaseous sulfur dioxide to bleach it and is then passed through filter presses.
The resulting clear juice is then evaporated in a partial vacuum and heated until it forms a thick syrup containing many crystals of sugar. The dense mass of crystals and syrup is known as massecuite. The massecuite is placed in a centrifuge turning at a rate of 1000 to 1500 rpm; the centrifuge walls are pierced by small holes through which the syrup, called molasses, is forced out during centrifuging.
The yellowish or brown sugar removed during the centrifuging process is called first sugar, or raw sugar. The first sugar is sprayed with water to remove any molasses that may have clung to the crystals, and is then moved to the refinery. The molasses may be boiled again and reevaporated in an attempt to crystallize out some of the rich sucrose content of this liquid; in modern cane-sugar manufacture, the syrup is usually crystallized only once. The molasses is a valuable by-product of the sugar industry, being used in the manufacture of ethyl alcohol and rum, as a table syrup and food flavoring, as food for farm animals, and in the manufacture of several processed tobaccos.
At the refinery, the raw sugar is redissolved, decolorized, and recrystallized into crystals of desired size. Powdered, granulated, and lump sugar, as well as brown sugars, which contain some molasses, are produced in the refineries.
SUCROSE FROM SUGAR BEETS
Sugar is manufactured from the roots of the sugar beet, the leaves and tops being removed after harvesting and used as stock feed. The roots are cut into cossettes, or chips, at the sugar factory, and the cossettes are crushed to remove the juice.
The pulp remaining after the extraction of the juice is a rich food for domestic animals. After extraction lime is added to the juice, and the remainder of the process is similar to sugar production from sugarcane.
Beet molasses is fed to livestock; no table molasses is made from beets because of difficulties in purification. The sugar that is produced from the sugar beet is identical to the sugar that is derived from the sugarcane.