CHEMISTRY OF RAW MATERIALS
The sugar industry processes sugar cane and sugar beet to manufacture edible sugar. More than
60% of the world’s sugar production is from sugar cane; the balance is from sugar beet. Sugar
manufacturing is a highly seasonal industry, with season lengths of about 6 to 18 weeks for beets
and 20 to 32 weeks for cane.
The primary raw material for the production of sugar is sugarcane. Sugarcane grows up to four
meters tall. It is cultivated for its stem. A mature stem is typically composed of 11-16% fibre, 1216% soluble sugars, 2-3% non-sugars and 63-73% water.
Sugarcane is a tropical grass belonging to the same tribe (andropogonae) as sorghum, Johnson
grass and corn (maize). More specifically, modern sugarcane is a complex hybrid of two or more
of the six species of the genus saccharum: s. barberi Jeswiet, s. officinarum L., srobustum
brandes and jesw. Ex Grassl, S. sanguinarum Grassl, s. sinese Roxb, and s. spontaneum L. many
forms of these species interbreed making highly diverse genus.
The goal of the sugarcane harvest is to produce sugarcane stalks of high quality. Quality is
reduced by damaging cane, increasing trash in delivered cane and delaying cane delivery.
Removal of cane tops is of prime importance in any harvesting operation. Cane tops have little
sucrose but are high in starch and reducing sugars. Starch and reducing sugars lower sugar
yieldin the boiling house and the residue from the tops absorbs sucrose and emerges from the
millswith more sucrose than when it entered. Cane leaves also have a high silica content and
contributes to mill wear.
The quality of sugarcane tends to improve with age, reaching maximum and gradually
declining.Rapid deterioration begins from the moment of harvest. Deterioration may begin
before harvest in pest-ridden cane or in fields affected by fire, freezes or wind storms.
After cutting, sugarcane loses water (1 to 2 % daily for the first week). This loss gives an
apparent but false increase in sugar content. The enzyme invertase, already present, converts
sucrose to reducing sugars thus lowering purity. Sucrose inversion varies with temperature and
moisture and is most rapid in hot, dry periods. Stale cane is anathema to the industry; growers
lose tonnage and processors lose sugars.
Unlike sugar beets, sugarcane cannot be stored for processing without excessive inversion; thus
harvesting and processing to raw sugar are concurrent.
COMPOSITION OF CANE AND JUICE
When cane is cut and cleaned by hand, and delivered fresh, processors receive the best possible
starting material for sugar production. Cane that is cut and loaded by machine invariably
contains tops, leaves stubble and roots, as well as soil, water and other extraneous matter.
Sucrose in the juice and cellulose in the fibre are the two main constituents of sugarcane and
both are made of simple sugars. The simple sugars glucose and fructose occur free in sugarcane,
usually in lesser amounts than sucrose. The production of sugar from sugarcane juice is based on
the ability of sucrose to crystallize from thick syrup while glucose and fructose remain dissolved.
Other sugars occur in cane but not in the free state; these are constituents of gums or cell walls.
Sugar, in the ordinary sense, is sucrose. It is the sugar of household and industry and is the most
common sugar in the plant kingdom. Sucrose occurs in all parts of the sugarcane plant and is
most abundant in the stalk, where it is found in the watery vacuoles of storage cells. The sucrose
content is lowest in the actively growing regions, especially the soft portions of the stem tip and
the leaf roll.
The monosaccharide sugars, glucose and fructose condense to form sucrose and water. Glucose
content exceeds that of sucrose only in the actively growing portion of the cane plant.
The glucose content of cane juice is high early in the harvest season, decreasing with maturation.
Also called fruit sugar, fructose is sweeter than sucrose and glucose but of the three, it is the least
abundant in cane. Like glucose, it is most abundant in the growing parts of the plant and least
abundant in the lower stalk and rots. Fructose decrease with maturity and may be undetectable in
some high purity varieties at maturity. Fructose is usually present in lesser amounts than glucose.
Fructose molecules condense to form inulin, a storage product of some plants.
In chemical sense, ` inversion’ means the changing of dextrorotatory optical activity to
levorotatory, or the converse. Usage in sugar technology has evolved a new meaning: the acidic
or enzymatic hydrolysis of sucrose to invert sugars. `inversion’ is wrongly but widely used to
refer to deterioration following severe burning or freezing when the sucrose is metabolized by
bacteria.