Sugar Production from Sugar Cane
Practical Action
of these have the effect of settling out impurities. Many producers also add 'hydros' (sodium
hydrogen sulphate) at the final stages of boiling. This releases sulphur dioxide into the juice and
lightens the colour of the final product. (Note that a high sulphur content often remains in the
final product.)
Filtration and Clarification
The amount of non-sugars such as bagasse and other particulates in the juice will affect its
purity, resulting in discoloration and reduced sweetness. Therefore filtration is essential and if
done with care can remove up to 60% of non-sugars from the juice.
A filter press, if available, will give the best results but can be expensive for small-scale
operations. However, reasonable levels of filtration can be achieved by allowing the juice to
stand for a few hours to allow particulates to precipitate out. The tanks should be fitted with a
fine mesh lid, through which the juice is poured to filter out large particles of bagasse and other
foreign bodies. The mesh will also prevent infestation from insects and help prevent
contamination by small animals and birds.
After settling the juice should be drawn from the tank ensuring that particulates settled at the
bottom of the tank are not disturbed. The juice can then be poured into the boiling pan through
a coarse cotton cloth to filter out fine particles that may remain in suspension.
Clarification, if undertaken, is carried out during the boiling process by adding a small amount of
vegetable or chemical matter to the juice. The clarificants do not react with the juice but
coagulate during the heating process, trapping particles and contaminants and bringing them to
the surface during boiling. This appears on the surface as a scum which can be removed using
long handled fine-mesh ladles or by passing a fine cotton cloth through the juice.
In India barks from the following plants are used:
Hibiscus figulneus
Hibiscus esculentus
Bombus malbaricum
Grewia asiatic
Kydia calycina
These barks are soaked in water and the resulting solution added to the juice just before boiling
commences. Approximately 10 to 15% of non-sugars can be removed using this method. These
barks may not be available else where and so some investigation is needed to find out what local
alternatives are available or traditionally used.
Boiling
For syrup production the juice is boiled until the required concentration is reached and the strike
is made at around 105ºC when most of the moisture has been boiled off and just before
crystallisation occurs. If the juice is over-boiled then crystals may be present which may cause
discoloration. If under-boiled, too much moisture will remain in the syrup which may, with time,
cause cloudiness and shorten its shelf life. For lump sugars the juice is boiled for longer and the
strike is made at between 116 and 120ºC.
In all cases the furnaces use sun dried bagasse as fuel. The bigger factories often have a surplus
at the end of operations while smaller units have to operate their furnaces with much greater
care to ensure that they do not use all the bagasse before boiling is completed.
8