Harvesting
Sugar cane is harvested by chopping down the stems
but leaving the roots so that it re-grows in time
for the next crop. Harvest times tend to be during
the dry season and the length of the harvest ranges
from as little as 2 ½ months up to 11 months.
The cane is taken to the factory, often by truck.
Extraction
The first stage of processing is the extraction of
the cane juice. In many factories the cane is crushed
in a series of large roller mills: similar to a mangle
[wringer] which was used to squeeze the water out
of clean washing a century ago. The sweet juice comes
gushing out and the cane fibre is carried away for
use in the boilers. In other factories a diffuser
is used as is described for beet sugar manufacture.
Either way the juice is pretty dirty: the soil from
the fields, some small fibres and the green extracts
from the plant are all mixed in with the sugar.
Evaporation
The factory can clean up the juice quite easily with
slaked lime (a relative of chalk) which settles out
a lot of the dirt so that it can be sent back to the
fields. Once this is done, the juice is thickened
up into a syrup by boiling off the water using steam
in a process called evaporation. Sometimes the syrup
is cleaned up again but more often it just goes on
to the crystal-making step without any more cleaning.
The evaporation is undertaken in order to improve
the energy efficiency of the factory.
Boiling
The syrup is placed into a very large pan for boiling,
the last stage. In the pan even more water is boiled
off until conditions are right for sugar crystals
to grow. You may have done something like this at
school but probably not with sugar because it is difficult
to get the crystals to grow well. In the factory the
workers usually have to throw in some sugar dust to
initiate crystal formation. Once the crystals have
grown the resulting mixture of crystals and mother
liquor is spun in centrifuges to separate the two,
rather like washing is spin dried. The crystals are
then given a final dry with hot air before being stored
ready for despatch.
Storage
The final raw sugar forms a sticky brown mountain
in the store and looks rather like the soft brown
sugar found in domestic kitchens. It could be used
like that but usually it gets dirty in storage and
has a distinctive taste which most people don't want.
That is why it is refined when it gets to the country
where it will be used. Additionally, because one cannot
get all the sugar out of the juice, there is a sweet
by-product made: molasses. This is usually turned
into a cattle food or is sent to a distillery where
alcohol is made.
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