Sugar Manufacture Process

1. Cane preparation
The cane is received and unloaded into the cane carrier, mechanically through grabs, tippers or
using manual labor. From cane carrier sugarcane is slowly conveyed to milling process through a
belt convayer. The milling process occurs in two steps, breaking a hard structure of cane and
grinding the cane. Cane juice is held in cells which has protective fibrous covering. For better
extraction the juice cells have to be broken and ruptured. For breaking the cane, it is fed into
revolving knives, hammer mill shredder, unigraders or fibriser or combination of these processes.
The fibriser consists of heavy duty cane cutting knives that break cane sticks to longitudinally
small shreds. The fibriser up 90 % of the juice cells which facilitates extraction of sugar from the
fiber in subsequent processing.
2. Milling
For grinding and milling, a uniform bed of crushed cane is pushed to multiple sets of three roller
mills. The rollers are so arranged in triangular set as to squeeze the cane mass twice under
pressure. Four to six sets of such mills make up a crushing tandem. Sugar mills may have one or
two tandems according to their crushing capacity. Some sugar mills have pressure feeder device
wherein cane is compressed to the mill through a chute under pressure. It helps enhance crushing
capacity as well as extraction.
In first mill almost 68 – 70 % of cane juice is extracted. To extract the remaining juice, residue of
the cane is passed from one mill to the other mills of the tandem. To accelerate extraction from
the shredded cells, some water is added on to the passing residue in a roller set of 4th or 5th mill.
This water which is more or less 200-250 % of the amount of fiber (worked out in due course) is
called imbibition’s water. The amount of imbibition water with juice and the steam requirement
are to be efficiently and economically controlled. Hot water temperature of 60º - 80ºC is
considered optimum for extracting most of the juice from cells than the use of cold water. The
water temperature higher than this dissolves waxes and is not desirable. The juice extracted from
the last mill is pumped and applied back to the previous mill and transferred from mill to mill
towards the first two mills. It is only from the first and second mills that the mixed juice is pumped
out, strained to remove large particles, weighed and sent for boiling and clarification.
After complete juice extraction, the sugarcane residue called 'bagasse' contains more or less 50
% moisture and the crushing process extracts 92 – 97 % of the sucrose present in the cane sent
to the mill. Bagasse from the final mill is conveyed out partly to the boiler and the rest to store
in a yard. It is used for fuel in boilers for producing high pressure steam for driving turbines for
the mills, shredders and power generation. The exhaust steam is used for heating and juice
evaporation. The ash is collected and sent out as waste material. It may be blended with filter
cake for use as organic manure in cane fields. From viewpoints of milling operation amount of
fiber in cane is of great economic significance. High fiber cane varieties with high sucrose may be
useful as more energy bagasse is saved. But extraneous matter in cane in the form of trash, tops,
roots and mud particles are extra drain on cane milling. The extraneous matter reduces
extraction as well as crushing rate. High dirt cause wear to shredders and rollers; milling efficiency
is reduced with increased maintenance cost.
 3. Clarification
The juice obtained through crushing cane contain many impurities including fibrous material, soil
particles, suspended colloidal matter, dissolved organic substances such as pigments
(chlorophyll, anthocyanin, polyphenols), wax, gums, albumins, proteins, pectin’s, starch, glucose,
fructose, minerals and amino acids. These have to be removed as for as possible. The pH of the
juice is basically acidic in nature which has to be raised to neutral level. Juice is heated to about
75ºC and is limed with calcium hydro oxide Ca (OH)² @ 0.06 to 0.10 % of cane weight. If needed,
additional phosphorus may be added as super phosphate. It is further heated to 102 - 105ºC. The
objective is:
a. To kill the bacteria to avoid possible infection and remove air.
b. To prevent inversion of sucrose which otherwise takes place in acidic medium.
c. To coagulate the impurities with suspended particles to form precipitate.

The heated juice is brought to clarifier where all the impurities and also calcium phosphate,
formed by milk of lime and naturally occurring phosphates in cane juice, coagulate to form flocks
and are precipitated as mud. Juice is then made to pass through clarifier where the impurities
are precipitated and settled down taking with it dirt, fiber particles and other organic substances.
Settling time should be the minimum to avoid charring of the juice. To enhance settling rate some
flocculants are added. The clarified juice in upper portion of the clarifier is drawn out and sent to
the evaporators. Precipitate that settles in the bottom of the clarifier is called “mud” and is
drained out. The presence of soil particles, juice from deteriorated cane or stale cane has
detrimental effect on clarification process. Poor clarification lowers sugar quality and has adverse
effect on crystallization process and finally increases sugar losses.
4. Filtration
For extracting juice from mud, it is passed through rotary vacuum filters. To further recover the
sucrose from the mud, it is mixed with bagacillo to make it porous. It is pushed to rotary drum
vacuum filters. Hot water is sprayed on rotary filters that helps remove maximum sugar from the
mud. The filtered solute is sucked and returned to clarifier, whereas the hard layer of residue is
gently scraped and is called filter cake or simply filter cake. The juice from the Vacuum Filter is
sent to defecation for processing. Fresh cake contains 75 – 80 % moisture and 0.5 % sugar. If
quantity of mud is more, sugar will be lost from the process. Lesser juice impurity would produce
lesser quantity of mud and low sugar losses.
5. Evaporation
Evaporation is performed in two stages, initially in evaporators to concentrate juice, then in
vacuum pan to crystallize sugar. The clarified juices are passed through heat exchange to preheat
the juice and sent to evaporation station. Evaporation station consists of a series of about 5
evaporates called multiple effect evaporation. Steam from power house is used to heat the first
evaporator, the vapor from the first evaporator is used to heat the second evaporator, and this
heat transfer process continues to the last evaporator. Pre-requisite of evaporators is to be
efficiently and economically controlled. Clear juice is pre- heated to a temperature around 107-
110ºC and is passed to the evaporator. In the second vessel it is heated at little low temperature
but under high pressure with vapors developed in the first vessel and then is passed on to the
third vessel.
 At this point juice temperature is reduced to about 85ºC but vapor pressure is almost 660 mm.
In the last vessel temperature would be about 65o C, vapor pressure 760 mm and syrup density
reaches 60-650 Brix and 85% purity just below the saturation point. The final out going product
is called syrup. Chemist at the spot control the heat transfer, the steam pressure, the vacuum
developed and the Brix of incoming juice and finally the syrup. During boiling operations, salts
and other substance foul the heating surface of tubes and are to be frequently cleaned out with
chemicals or mechanically.
6. Pan boiling
The syrup from evaporators passes through crystallization stage together with seed. The
crystallization process is carried out in vacuum pan, which may be batch or continuous in
operation. The contents are boiled under vacuum at about 60ºC. During boiling as the magma
concentrates, C sugar (seed) is added to initiate crystallization of sugar. Crystals in mother liquor
grow to achieve requisite size. The boiling action continues with the formation of crystals in
mother liquor. As the crystal size is achieved new syrup is added. This is a critical stage and has
to be carefully monitored. This process produces sugar crystals and concentrated syrup called
molasses, and whole mass is termed as masseccuit. Whole operation is completed in three stages
of syrup boiling system producing A, B and the 'C' sugars. The 'A' and 'B' sugar constitutes raw
sugar while C sugar is recovered in the lowest purity boiling and is typically used as the starting
crystals (seed for A and B sugar boiling).
The process of crystallization may be hampered by impurities in juice especially dextran.
Efficiency of pan boiling process is affected by level of impurities and the sugar in the syrup. High
level of impurities imbalance the production of A and B massecuite with special reference to time
frame for boiling. The technologists have to set the pan boiling system based on cane crushing
capacity, and considering the purity level of cane juice.
7. Crystallization
Vacuum pan boiler is equipped with a steam heated calandria (tubes for syrup flow) and a
condenser to maintain vacuum. Syrup is charged into the evaporator to about one third of its
capacity. Syrup at this stage is viscous mixture of fine sugar crystal and syrup, called as massecuit.
It is super saturated to form crystals, and is then seeded with additional powdery sugar crystals
to start the crystallization process. As the water is evaporated more syrup is added. The process
of crystals growth to a desired size is carefully watched. When the pan gets full to the desired
crystal size and mother liquor (90- 94º Brix), the massecuite is discharged into crystallizer. In the
crystallizer the temperature is kept low to allow crystallization.
8. Separation of sugar
As the crystallization is complete, the massecuite is subjected to the centrifugal for separation of
sugar from molasses. The centrifugal speed is at about of 1600-2100 RPM. The sugar is screen
while the molasses is drained out. To clear the sugar from adhering molasses it is slightly sprayed
with water at 85ºC. The sugar crystals should preferably be uniform in structure. The centrifugal
now in use are fully automatic, having charging, washing, spinning, de-loading and restarting
steps. They have the capacities of 500 to 1000 kg of masseceuite per charge with 15-20 cycles
per hour.
It is 'A' grade sugar and A-heavy molasses. In order to get possible maximum sugar from
the syrup, series of graded massecuite A, B and C are gradually boiled to achieve maximum crystal
contents at appropriate stage. For refine centrifugal the recommended speed is 1200 RPM.
Refined sugar
Most of world sugar is marketed as raw sugar. The countries like Cuba, Brazil, Mauritius, Thailand,
Australia, mostly produce and market raw sugar. The raw sugar is refined to make it free of all
impurities according to the taste and standards of consumers. A number of processes are
involved in refineries.
Refinery Process
1. Carbonation of raw liquor
Carbonation process is carried out by adding milk of lime (calcium hydroxide), Ca (OH2) to the
liquor and bubbling carbon dioxide through gas coils, which reacts with the lime to form fine
crystalline particles of calcium carbonate. To obtain stable flocks, the pH and temperature of
reaction are carefully controlled in the range of first stage 9.2 – 9.4 and in second stage 8.2 – 8.4.
2. Phosphitation of carbonated liquor
5 % diluted phosphoric acid added in the carbonated liquor to stable the non-sugar precipitates
(Tri calcium carbonate and Tri calcium phosphate) and reduce the pH level 7.2 to 7.4. Separation
of flocks is carried out by filtration the liquor through pressure filters.
3. Filtration of carbonated liquor
Carbonated liquor passed through pressure filters for the separation of Tri calcium carbonate, Tri
calcium phosphates and obtains clear liquor maintaining the pH value 7.2 to 7.4.
4. Sulphitation of clear liquor
Sulphitation of clear liquor takes place in sulphitor liquor column where SO2 gas sucked by
vacuum creation. Gas acts as bleaching agent to remove the coloring matter and produces
shining and transparent liquor, before filtering the liquor pH maintained at 6.4 to 6.6.
5. Filtration of sulphated liquor
Sulphated liquor passed through pressure filters for the separation of ferrous sulphate
precipitates and obtains fine liquor, maintaining the pH value 6.4 to 6.6.
Production of refine massecuite -1
R-1, refined massecuite produced in the vacuum pan under vacuum boiling condition liquor and
the seed taken in pan is boiled to produce the refine massecuite by means of. vapors from vapors
cell, maintaining the desired Brix 88 to 89º.
Production of refine massecuite -2
R-2, refined massecuite produced in the vacuum pan under vacuum boiling condition run off-1,
seed (cut seed obtained from other pan) taken in pan is boiled to produce the refine massecuite-
2, by means of vapors from vapors cell maintaining the desired Brix 89 to 90º.
Production of refine massecuite-3
R-3 refined massecuite produced in the vacuum pan under vacuum boiling condition run off-2,
seed (cut seed obtained from other pan) taken in pan is boiled to produce the refine massecuite-
3, by mean of vapors from vapor cell maintaining the desired Brix 90 to 91º.
 6. Centrifuging (purging of refine massecuite)
Refine massecuite charged in TSK centrifugal machines for the separation of sugar crystal and
from run off by means of spray hot water of 90ºC through spray nozzles. Sugar crystals separated
in the form of refine sugar and molasses in the form of run off.
7. Sugar drying and bagging
Sugar when discharged from centrifugal may have moisture of 2 % and temperature of 70-75ºC.
The sugar is subjected to a bucket elevator on a conveyer. Hot air is blown as a counter current,
where the sugar is completely dried. The sugar must give white luster and transparency. The
sugar is then passed through a continuously shaking sieve. The crystals having larger size are
separated for re-melt processing. Fine grain is used as seed in the refine pan, bold and medium
grain is bagged, weighed and sent to godown for storage and marketing.