Cassava processing
Practical Action
about 20 to 25 kg of roots in an hour. Around 30% of the fresh weight is lost during the manual
peeling, when woody tips are also removed.
Various peeling machines that have been developed but they have not been universally accepted
because the cost is too high for many small-scale producers and the machines result in too much
wastage in the peeling process. The peeled roots then need to be washed to remove dirt and
pieces of peel.
The peeled tubers are next chipped, grated, sliced, cubed or pelleted before further processing
can take place.
Chipping
If the chips come from bitter cassava varieties, the roots are often kept in water for 2 to 4 days.
This allows hydrogen cyanide to be released, reducing any public health hazard. The water must
be carefully disposed of afterwards. Chipping can be done manually or with chipping equipment.
Grating and Rasping
Cassava is frequently grated or rasped as part of
its processing. Traditionally it was a laborious
activity carried out by hand. Now there is a large
range of graters that can be used form the most
basic manual and pedal operated graters
through to fully motorised machines.
Drying
Cassava chips have to be dried to a moisture
content of around 12 to 15%; from the original
moisture content of 65 to 75%. Once dried the
chips should break easily without crumbling.
If no other storage method is used drying should
take place within 2 days of harvesting to ensure
that the quality of the product is maintained.
Cassava chips are often infested by insects
Figure 3: A cassava chipper
Illustration: Neil Noble/Practical Action
during the drying process so the time taken to
dry the chips is important. The drying process can be shortened by increasing the surface area of
the chips in relation to their volume - so the smaller the chips the faster the drying time. The
larger chips therefore have to be reduced in size to improve their drying properties.
Traditionally cassava has been sun dried in the open air, either on the ground or on a raised
platform. Solar drying techniques improve upon this traditional approach by protecting the
product from the elements and by improving the airflow which reduces the time for drying.
Artificial drying can be used when the climate is not reliable enough or where the humidity is too
high to use solar drying equipment. Artificial dryers are common as they are more predictable
and controllable. Practical Action has developed various designs of tray dryer that can be used to
dry fruit and vegetables and would be suitable for drying chopped cassava. Here economic factors
must be considered as artificial dryers use fuel.
Making cassava flour
As flour, cassava can be stored up to a year if properly
packaged. Traditionally cassava flour is made by pounding
chips with a pestle and mortar. The process involves
softening the tubers, cutting, drying and then pounding
again or milling.
The moisture content is high so the roots need to be
dewatered, which can remove up to 50% of the water. This
can be done by various types of press. The more simple
types consist of parallel press boards that can be screwed
together. Hydraulic jack presses can also be used. The
The basic steps for
making flour
Sort
Peel
Wash
Grate
Dewater
Pound or mill
Dry
Fine mill
Sieve
Pack
4