As carriers of carbohydrates, tropical roots and tubers
contribute greatly to securing the basic nutrition. This particularly applies to
the countries of the humid tropics in Africa where this group of products often
secures over 50% of the nutrients for local populations.
Judged by the area on which they are cultivated and the total
yield, cassava and yams are the most significant roots and tubers in Africa.
Therefore this work concentrates on these two crops.
Tropical roots and tubers have a high output per unit area and,
with the exception of yams, have low demands on soil quality. They are marked by
high resistance to drought and low susceptibility to mass pests.
These properties are the reason why roots and tubers have a firm
place in small farm systems. Here, they contribute to reducing the risks
involved in cultivation and frequently serve the purpose of providing nutrition
In contrast to specific advantages in production, roots and
tubers have negative storage properties mainly resulting from the high water
content of their storage organs. High losses are consequently a feature of their
post-harvest behavioural pattern.
The bad storage properties have thus contributed to traditional
societies searching more for measures to avoid storage than for measures to
improve this. To avoid storage in a fresh state, the roots and tubers are
frequently processed into dry products which will keep.
Traditional storage systems for fresh products have been
developed for yams in particular whose tubers have a natural storage quality due
to their dormancy. These systems are all very simple in design 'end have often
remained unchanged over a long period.
Improvements to traditional storage systems for fresh yam tubers
are possible. These must begin at the time of harvesting when tubers should be
handled carefully so that uninjured tubers can be put into storage. Small
technical improvements to keep away pests, to improve the climate in storage and
to facilitate regular control of the stored produce can contribute substantially
to reducing losses.
The lack of storage ability of fresh cassava roots is caused
mainly by physiological processes leading to fast destruction of the root
tissue. All experiments to substantially prolong the storage of fresh cassava
roots so far have not been convincing.
The only possibility of storing fresh cassava roots consists of
leaving them in the ground after the harvest. In this way, the roots can be
"stored" for several months without showing any great losses. However, this
blocks land for the cultivation of other crops.
The most simple method of overcoming the lack of storage ability
in fresh cassava roots is to produce dried chips. This is a traditional process
and is widespread in Africa. The storage of cassava chips can be improved
particularly by reducing the process of drying which frequently takes several
weeks. This can take place by preparing smaller chips and by making use of the
energy from the wind and the sun for drying.
Storage of the dried chips with a remaining moisture content of
12% should be in insect-proof containers. The definition of suitable storage
systems, of both traditional and modem design, and the measures of chemical
storage protection, both require more detailed examination before
recommendations can be made on applying these to cassava