5.6.3 The production of cassava chips
The production of cassava chips is the most simple way of
obtaining a product, on the basis of cassava, which will keep and which can be
stored. Cassava chips are for the purpose of self-sufficiency, as e.g. in West
Africa (STABRAWA, 1991) as well as for obtaining income and foreign currency.
The latter applies particularly to Thailand (COCK, 1985).
The production process always follows the same pattern and more
or less shows a high degree of mechanization. Slight deviations from this lead
to chips with varying quality features reflecting the regional demand and
flavour preferences. The possible variations on the standard processes here,
will be dispensed with at this point. Firstly, these are far too numerous,
often-only of regional importance, and secondly, documentation on this is rare.
Chips are not only made from cassava but can also be produced
from yams. Due to the lower content of dry matter in yams in comparison to
cassava correspondingly more energy has to be used to dry them. Seen from the
volume of production, cassava chips are far more significant than yam chips. As
the production processes for both products are virtually identical the method of
producing yam chips is not to be discussed at this point.
220.127.116.11 Preparation of the cassava roots for the production of
The cassava roots are peeled immediately after harvesting with
the traditional cutting tools, e.g. brushwood knife (machete). The peeling,
mainly carried out manually by women, requires a great deal of work. One woman
can peel about 20 -25 kg roots in one hour (SADIK, 1987). The loss in weight
occurring due to peeling amounts to about 30% of the fresh weight (ibid.).
Various peeling machines have been developed in West Africa.
These have not been widely accepted because the purchase prices are too high and
the machines cause too great a loss in peeling (ibid.).
The roots peeled are men washed. If the chips are obtained from
bitter cassava varieties, the roots frequently are kept in water after peeling.
This causes hydrogen cyanide to be released, reducing the danger of poisoning
(JAKUBCZYK, 1982). For a sufficient release of hydrogen cyanide, the roots
should be soaked for 2 - 4 days (JOSEPH, undated). A good release of hydrogen
cyanide is attained if the roots are cut into pieces prior to soaking. These are
men soaked in water for 15 minutes and then boiled for 2 minutes (JAKUBCZYK,
Another method of preparation is to briefly boil the freshly
peeled roots in water. Then they are halved lengthwise and soaked in water for 1
- 2 days. The water should be changed once to twice during this time (ONWUEME,
Which process is preferred, particularly regarding the release
of hydrogen cyanide, has not yet been sufficiently investigated.
The cassava roots prepared in this way are cut into pieces for
drying. How the roots are split up and how large the pieces are, vary from
region to region and depend on the relevant eating. The size of the pieces of
root is also influenced by climatic drying conditions. Thus the pieces are
mostly larger in the dry northern parts of Ghana man those in the south of the
country (KWAKU, 1991).
In some cases the cutting of the roots has also been mechanised.
The machines used for this chip the roots into small pieces which dry
correspondingly well (COCK, 1985).
18.104.22.168 Drying the cassava chips
To store well, the chips have to be dried to a moisture content
of about 12% (COCK, 1985). Completely dried chips are white and break easily
without crumbling (INGRAM and HAMPHRIES, 1972). Drying is frequently inadequate
when the chips are to be sold directly after they have been dried (INGRAM and
HAMPHRIES, 1972). Pricing which is oriented to the weight of the product, can be
manipulated in favour of the seller by increased moisture content.
The prepared chips are spread out on all sorts of supports to
dry. They are laid out on the roofs of houses, the edges of roads or in yards.
No special constructions developed for chip drying are known of in West Africa.
Chips laid out to dry are often soiled by rain, sand and animal excrement which
leads to losses in quality due to hygiene (JAKUBCZYK, 1982).
The energy from the sun and wind are mainly used to dry the
chips. High energy costs normally make the use of external energy (wood and
fossil fuels) to dry the chips unviable. The drying process however, is often
supported by wood fires and the use of heat from stoves (CHINSMAN and FIAGAN,
1987). The smoke emitted is said to act as an insecticide. But smoke also leads
to discolouring and changes in the flavour of the chips which is not always
The duration of drying depends on the size of the chips and on
climatic conditions. Under optimum conditions. the chips can be completely dried
within 2 days by using the energy from the sun and the wind (COCK 1985 )However
the drying period is mostly much longer and frequently takes between two and
three weeks (INGRAM and HAMPHRIES, 1972).
During the long drying period the chips often become mouldy and
ferment. This makes the originally white chips discoloured and also changes
their flavour. The Ada, an ethnic group native to Ghana, want this qualitative
change to take place during drying (NICOL 1991). In the opinion of the Ada, the
fungus settling on the chips is evidence of a low content of hydrogen cyanide.
Consequently, they believe that chips infested by mould are quite suitable for
human consumption (ibid.). Mould as an indicator for the non-toxicity of chips
has not yet been proven scientifically.
Chips are often briefly boiled in water (parboiled) after drying
and men dried again. This makes the chips harder and is to improve their storage
ability and reduce their susceptibility to infestation by pests. Investigation
however show varying results (STABRAWA, 1991;INGRAM and HUMPHRIES, 1972).
22.214.171.124 The storage of cassava chips
The demands cassava chips have on storage conditions are similar
to those of cereals (COURSEY, 1982). Cassava chips are hygroscopic and tend to
draw moisture which promotes the formation of mould and thus early
Many stored product insects which cause damage to cereals also
infest cassava chips (cf. Chapter 126.96.36.199). Consequently, storage structures
should on the one hand provide some protection from reabsorbing moisture, but
should also avoid infestation by pest insects. This must be qualified by saying
that cassava chips are often infested by pest insects during the drying process.
For this reason, as already mentioned in Chapter 188.8.131.52, the drying process is
of particular importance in the storage of chips.
In contrast to the yam tubers for which specific storage systems
have been developed, cassava chips are kept in stores which are also used to
store cereals and grain legumes (STABRAWA, 1991). Thus, cassava chips are stored
in baskets, in wooden containers, in sacks or in bulk in storage rooms as well
as in various traditional storage systems intended for cereals (INGRAM and
HAMPHRIES, 1991). Frequently varying storage systems are used side by side which
can serve to fulfill the varying storage requirements (STABRAWA, 1991).
Of great importance in the selection of certain storage systems
are the availability of various building materials, the existence of certain
artisanal knowledge, capital and labour. In contrast, cultural customs and
traditions play only a minor role (COMPTON, 1991). In many areas, there are
however skill close associations between the structural features of storage
systems and certain ethnic groups. These are normally a result of artisanal
traditions and experience being passed down within certain groups. This
experience is also freely passed on to members of other groups and used by these
('bid.), indicating some openness regarding technical storage innovations.
In Togo, there are three traditional types of storage in
particular which are preferred for storing cereals but also for cassava chips.
Fig 16: "Kpeou", a traditional storage
system for cassava chips (Source: LAMBONI, undated)
The "kpeou" is a storage structure which consists of mud or
often of the material from termite mounds. It is shaped like a water jug and is
often divided into several chambers (Fig. 16). The store often reaches a height
of over 2 metres. The upper edge of the "kpeou" has an opening for filling and
entering which can be firmly closed. The "kpeou" is relatively expensive to
erect but has a service life of 20 - 30 years. In Togo the "kpeou" is the only
closed storage system. As there is no method of ventilation due to the way of
building, the produce which is to be stored must be dried optimally (chips
should not have a moisture content greater than 12%).
Fig. 17: "Katchalla", a traditional
storage system for cassava chips (Source: LAMBONI, undated)
The "katchalla" is made of wood and straw. It looks like a cone
which is upside down and is stabilized by wooden supports (Fig. 17). The
"katchalla" has an opening at the peak of the cone which is closed by a conical
roof. The storage system is not airtight, but has some ventilation.
The "tonneau" can be compared to a large barrel and is erected
on a low platform. The "tonneau" consists of a wooden frame in which mats are
stretched. The "tonneau" is open at the upper edge and is closed by a conical
roof (Fig. 18). It is often constructed to a height of more than 2 meters. This
system is also open and allows air exchange between the stored produce and the
Fig 18: "Tonneau", a traditional
storage system for cassava chips (Source: LAMBONI, undated)
According to the studies by COMPTON ( 1991 ) and STABRAWA
(1991), about 60% of cassava chips are stored in traditional storage systems
(34% "kpeou" and 26% "katchalla) in the central region of Togo. The remaining
40% are kept in varying types of storage of which storage in sacks and as bulk
produce in storage rooms are the most significant.
The average storage duration for cassava chips amounts to 7
months, but can extend to over one year (STABRAWA, 1991). Other sources state a
storage duration of 3 - 6 months for sun-dried and of up to 12 months for
"parboiled" cassava chips before serious mould begins (INGRAM and HAMPHRIES,
The duration of storage is influenced by a large number of
factors which can vary greatly from region to region. In addition to natural
influences, the duration of storage is also affected by socio-economic factors.
In Togo, for example, the chips which are intended for sale are stored for 7 - 8
months in order to take advantage of price fluctuations due to quantities in
supply. Chips serving self-sufficiency purposes are stored up to a period of 12
months, i.e. until the new harvest is brought in (STABRAWA, 1991).
184.108.40.206 Losses in storage due to pest insects
Stored product insects cause high losses in the storage of
cassava chips. These pests infest not only cassava chips but also other foods
which are stored under tropical conditions (HODGES et al., 1985). According to
LAMBONI (undated), Prostephanus truncatus (Horn), Dinoderus minutus and
Tribolium sp. are among the most significant pest insects in the storage of
cassava chips among small farmholders in Togo.
Prostephanus truncatus (Horn) which did not appear as a pest in
Togo until the beginning of the eighties, can be easily confused with Dinoderus
which also causes damage to stores of cassava chips (STABRAWA, 1991). The losses
caused by Prostephanus truncatus (Horn) can be very high. HODGES et al. (1985)
determined weight losses of up to 50% for unfermented and up to 70% for
fermented chips after a storage period of 4 months which were ascribed to this
The differences in the amounts of loss are caused by the varying
density of the two types of chips. Unfermented chips are denser making it more
difficult for the grain borer to penetrate them man fermented chips. The
production of unfermented chips cannot be recommended as protection from
infestation by Prostephanus as these are also subject to serious infestation
(HODGES et al., 1985).
To quantify the storage losses for cassava chips which are
caused by insects is very difficult as firstly, suitable methods for an
estimation of the losses do not exist. The NRI has been endeavouring to find a
basis for a solution to this for some time now. Secondly, the farmers evaluate
the losses of cassava chips due to insects in a different way than for e.g.
maize. The badly damaged chips and the flour from boring are mostly still used
for human consumption, the insects being sieved out beforehand (STABRAWA, 1991).
The farmers consider the worse plasticity of the cassava paste made from this to
be a considerable disadvantage of this insect infestation in comparison to that
made out of uninfested chips (COMPTON, 1991). Since only a third of the paste
mixture consists of cassava chip flour, the negative effect of the insect on the
consistency of the paste is limited (ibid.).
Insects often infest the chips during drying (cf. Chapter
220.127.116.11). They can also not infest the stored produce until it is put in
storage. Since farmers consider the losses caused by the insects only as partial
losses, practically no traditional preventive measures have been developed. In
particularly the high losses caused by Prostephanus truncatus (Horn) have led to
isolated farmers making use of chemical products for storage protection
(COMPTON, 1991). The selection of insecticides is made at random and depends
only on market supply. So far, the effect of these products and the formation of
possible residues which could constitute a health hazard have not been
investigated. For this reason, no insecticides, dosages or application methods
can be recommended here.
18.104.22.168 Storage losses due to mould
Mould frequently infests the cassava chips during the drying
stage. However, mould also forms if the chips again become moist in storage
(INGRAM and HUMPHRIES, 1972). Not only one variety of fungus but several occur
on the chips simultaneously. It teas not yet finally been determined which
metabolites form the various varieties of fungus, or whether mycotoxins are
possibly among these.
The formation of mould cannot be basically seen as a loss in
quality or a cause of loss. Some ethnic groups appreciate infestation of the
chips by mould and even speak of improvements in the flavour here (cf. Chapter
22.214.171.124). In Burundi, a Belgian company attempted to improve the nourishing
qualities of cassava chips by directed mould infestation (JOSEPH, 1986).
Disregarding the regionally varying preferences for particular flavouring, mould
on chips mostly leads to distinct losses in value. This applies particularly if
the chips are intended for sale. For these reasons the only recommendation at
this time can be to avoid the formation of mould on chips during production.
126.96.36.199 Measures to improve the production and storage of
The storage ability of cassava chips is strongly influenced by
the drying process. Drying which takes too long, promotes insect infestation
leading to extensive storage losses. If the chips are only insufficiently dried
and still have mote than 12% moisture content, the danger of mould will exist.
Mould also forms when the hydroscopic chips are not sufficiently protected from
the moisture in the atmosphere and re-absorb moisture during storage.
Improvements to the production and storage of cassava chips have
thus to begin at the drying stage. At the same time, a storage has to be
practiced which not only has to provide protection from the penetration of
insects, but also against re-moisturising of the stored products.
Peeling the cassava roots requires a great deal of labour. The
mechanisation processes devised so far are more for peeling large quantities
(e.g. for gari production) man for use on small farms. A technology which saves
labour and hardly causes any extra costs, which substantially improves the
labour productivity of peeling and thus seems predestined for introduction to
the a.m. target group is the peeling knife developed by the IITA. In Togo at
least, this knife is not widespread and should thus be put to practical tests as
a measure of improving the labour productivity. A direct contribution to
relieving the woman of labour could be made here since the peeling of the roots
is her responsibility.
The drying process can be shortened by increasing the surface
area of the chips in relation to their volume. The larger chips which are often
spread out to dry in many regions of Africa have to be reduced in size to
improve their drying properties. The principle to be followed here is: the
smaller the chips, the faster drying takes place.
Before measures can be recommended, the reasons for the size of
the chips must be investigated. If mere are reasons for this which stem from
work management, it must be investigated whether a technology can be introduced
to increase labour productivity. In this respect, the microeconomic viability
has to be analysed just as the acceptance of the procedure by the population
concerned. Examples of mechanisation for chip production using slicers can be
seen in work by COCK (1985) amongst others.
In the past, only the rays of the sun were normally used for
drying the chips. These are extensively reflected by the white chips and are
partly lost for the drying process. As experiments have shown, drying can be
substantially improved if wind energy is also used in addition to the energy
from the sun (COURSEY, 1982).
For this purpose the chips are laid out to dry on a wooden frame
covered with wire mesh. The frame can be any size but should be chosen so mat it
can be easily handled. This is the case when it is has an approximate size of
1.5 x 1 m. The wire used to stretch over the frame should be fine enough to
prevent the chips falling through the mesh. This wire can be substituted by any
locally available materials which can be permeated by air.
The wooden frames are set up at a definite angle so that the
rays of the sun fall on the chips and so that the natural movement of the wind
constantly aerates these (cf. Fig. 19). In this way, cassava chips can be
optimally dried within 2 days (COCK, 1985).
In addition to this mobile frames offer further advantages. If
unexpected rain showers occur, they can be cleared away with the chips which
prevents with during the drying process and thus a reduction in quality. There
are also hygienic benefits of using the frames since the chips no longer come
into contact with the dirt from the streets or the yard as is usual in
traditional drying processes.
Storage structures where chips are traditionally stored do not
always provide sufficient protection from pest insects or with Of the
traditional storage structures used in Togo, the "kpeou" (cf. 188.8.131.52) seems to
be suitable for the storage of cassava chips. However, the storing features of
this structure must be investigated in more detail. Apart from this traditional
system, other containers can be used to store cassava chips under some
circumstances. Literature mentions e.g. plastic sacks. Plastic barrels and used
oil barrels also seem suitable for storing cassava chips. The storage properties
of these must be initially investigated before any recommendation for storage in
these containers can be made.
There are no proven results on processes of chemical storage
protection for cassava chips. From Togo, it is known, and this definitely also
applies to other countries as well, mat the farmers use chemical insecticides
for cassava chips at random when pest infestation occurs. Since considerable
health hazards can occur when treated chips are consumed, investigations should
be carried out to define recommendations on products and on application which
will men allow storage protection without any risk to