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		Traditional Storage of Yams and Cassave and its Improvement (GTZ)
			(introduction...)
			Preface
			1 Introduction
			2 Socio-cultural aspects involved in the production of roots and tubers
			3 Basic comments on the storage properties of roots and tubers
			4 Yams
			5 Cassava
			6 Summary
			7 Bibliography

3 Basic comments on the storage properties of roots and tubers

In contrast to cereals which have good natural properties making them suitable for storage, tropical roots and tubers are, without exception, perishable crops The factors determining the difference between these two product groups and their storage properties can be seen in Table 5

From the varying determinants affecting the storage behaviour of these two groups of products it is evident that storage methods which have proven suitable for durable food crops cannot simply be applied to perishable crops. In addition, the roots and tubers are not a homogenous group where their storage properties are concerned but show varying differences specific to each product. It therefore becomes necessary to develop specific storage methods for each root and tuber, which is illustrated by the great variety of traditional storage systems.

It is for this reason that this investigation will proceed to treat both crops, yams and cassava, in separate sections

Table 5: Comparison of cereal storage properties with those of roots and tubers

Durable food crops

Perishable food crops

pronounced seasonal harvest, long-term storage necessary

continual or semi-continual harvesting possible. Long-term storage this often avoidable

processing (apart from threshing) to prepare the produce rarely necessary

processing to dried products often an alternative to storing fresh produce

low moisture content of crops, mostly between 10 - 15% or less

high moisture content of crops, mostly between 50 - 80%

small units mostly weighing less than 1 gramme

large units, mostly weighing between 5 g and 5 kg or more

slow respiratory activity of stored crops and thus low development of heat

high to very high respiratory activity of stored crops, consequently great degree of heat development particularly under tropical conditions

hard condition of tissue, good protection from injury

soft condition of tissue, easily injured

stable, good natural preservation, storage possible over several years

perishable, natural preservation of up to several months (great variations in species and varieties)

storage losses mostly exogenous (mould, insects, rodents)

losses partially endogenous (respiration, transpiration, germination), partially exogenous (rot, insects)

Source: FAO, 1984 (modified)

Durable food crops	Perishable food crops
pronounced seasonal harvest, long-term storage necessary	continual or semi-continual harvesting possible. Long-term storage this often avoidable
processing (apart from threshing) to prepare the produce rarely necessary	processing to dried products often an alternative to storing fresh produce
low moisture content of crops, mostly between 10 - 15% or less	high moisture content of crops, mostly between 50 - 80%
small units mostly weighing less than 1 gramme	large units, mostly weighing between 5 g and 5 kg or more
slow respiratory activity of stored crops and thus low development of heat	high to very high respiratory activity of stored crops, consequently great degree of heat development particularly under tropical conditions
hard condition of tissue, good protection from injury	soft condition of tissue, easily injured
stable, good natural preservation, storage possible over several years	perishable, natural preservation of up to several months (great variations in species and varieties)
storage losses mostly exogenous (mould, insects, rodents)	losses partially endogenous (respiration, transpiration, germination), partially exogenous (rot, insects)