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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 during bottlenecks.
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 chips.