Sucrose is a disaccharide that occurs naturally in most fruits and vegetables.
Sugar occurs in greatest quantities in sugarcane and sugar beets from which sugar is separated economically and commercially.
Chemical formula – c12H22O11
Molecular weight – 342
Density = 1.58 kg/m3
Sucrose is soluble in water but slightly soluble in methyl alcohol and ethyl alcohol.
Process flow sheet: Illustrated in Figure.
Figure 28.1 Flow sheet of manufacture of sugar from sugarcane
Raw material: Sugar cane
28.2 Functional role of various processes (Figure 28.1)
(i) Series of Pressure mills
(k) Rotary filter
(l) Multieffect evaporator
28.3 Technical Questions
1. What is special about the sugar production process from sugarcane
Sugarcane is a biological resource for sugar. If sugar is used for the production of alcohols which can be in turn used as fuels in modern cars, then the original source for obtaining these fuels is the agricultural industry. In other words, a biological source for fuels is an interesting technological concept for energy requirements of the modern society. On the other hand, over consumption of sugars for fuel requirements could enhance sugar demand for food usage and could spiral up the prices of the sugarcane. Therefore, a careful policy needs to be adopted for the utilization of sugar towards various process routes and technologies.
2. Why last effect evaporator is maintained at 63cm vacuum?
3. What is the technical difference between sulfitation and carbonation clarification process?
Ans: Sulfitation process is based on large quantities of sulfurous acid with proportional quantity of lime. Calcium sulfite formed prevents oxidation and darkening of juice. It also precipitates gums and albuminous matter thereby it helps in filtration.
In this process at about 65°C, SO2 gas is bubbled to juice to slightly increase acidity. The juice is then heated to boiling point for 2 hours. After sulfitation process, PH becomes 7 and concentration becomes 12 to 13 Brix.
In carbonation process, 1 to 1.5% of lime by weight at 50 to 55°C is added to the juice. CO2 gas is bubbled to remove alkalinity. The temperature is raised to the boiling point to remove excess carbonic acid.
4. What are the byproducts of sugar industries?
Ans: Bagasse, filtercake and molasses.
5. Discuss energy economy in the sugar manufacturing process?
6. What is the problem in storage of sugarcane?
Ans: There should be no delay in transporting freshly cut sugarcane to sugarmill because after 24 hours of cutting causes loss of sucrose by inversion to glucose and fructose (monosaccaharides).
C12H22O11 + H2O → C6H12O6 + C6H12O6
Sugar glucose fructose
The extent of inversion is measured by polarimeter. The non inverted sugar has +97° polarization and completely inverted sugar has -20° polarization.
This inversion of sucrose is maintained by quick delivery of freshly cut sugarcane to sugar mills.
7. Why vacuum pan crystallizer is used?
Ans: With the use of vacuum pan crystallizer, the pressure is reduced so as to super saturate the sugar solution. After supersaturation the formation of crystals starts. When the volume of massecuite (sugar solution 16crystals) exceeds certain limit, then it is transferred to centrifuge for separation.
8. What are the environmental problems faced by sugar industries.
Starch consists of a chain of D-glucopyranosyl units. It is used in the manufacture of textiles, paper, adhesives, insecticides, paints, soaps, explosives, and derivatives as dextrins, nitrostarch and corn sugar.
Chemical formula- C6H10O5 Starch gets hydrolysed by acids, alkalis and enzymes giving dextrin, dextrose. Starch forms gels with water within several minutes at 60-80˚C.
The major source of starch is maize kernels.
Process flow sheet: Illustrated in Figure.
28.4.2 Functional role of various processes
(a) Air cleaner:-
(b) Steeped tank:-
(c) Grinding mill:-
(d) Buhrstone mill:-
(e) Nylon screen:
(f) Two stage centrifuge:
(g) Rotary filter:
28.4.3 Technical Questions
1.How is degermination carried out?
Ans: To free germs the maize kernels are coarsely ground in mill with cane to avoid oil leakage from germs otherwise oil will get soaked up with starch granules, which reduce starch quality. Lighter germs are separated by hydrocyclones.
For complete degermination, grinding and degeneration steps are performed twice. Then the germs are washed, dried and sold for corn oil production.
2.What is the use of steep water?
Ans: Concentrated steep water is consumed in the growth of penicillin and streptomysin. Steep water softens the kernels and release solubles.
3.How is gluten removed?
Ans: Gluten is starch milk, which contains water insoluble proteins. It is mostly separated by two successive nozzle type continuous centrifugal separators. The separation occurs due to density difference between starch and protein.