1.0 Introduction 2.0 Objective
3.0 Methods of Storage of Crop 3.1 Cereals and Pulses
3.1.1 Conditions of storage 3.1.2 Methods of storage 3.2 Cassava
3.2.1 Conditions of storage 3.2.2 Storage practices 3.3Yam
3.3.1 Curing 3.3.2 Storage 3.4 Sweet potatoes
3.4.1 Curing 3.4.2 Storage 3.5 Irish Potatoes
3.5.1 Storage conditions 3.6 Oil containing products
3.6.1 Drying
3.6.2 Storage methods 5.0 Conclusion
5.0 Summary
6.0 Tutor Marked Assessment
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7.0 References and Further Reading
1.0 Introduction
High temperature and high moisture are the most significant factors affecting grain quality in storage. Each can cause rapid decline in germination, malting quality, baking quality, colour, oil composition, and many other quality characteristics.When dried to moisture contents below the safe moisture level, cerealsand pulses can be stored for periods of a year or more under a widerange of temperatures, provided that during storage the moisture leveldoes not rise, and precautions against insects are taken.
Crops producing root or stem tubers, have special requirementswith respect to storage, because of the high moisture content ofthe tubers (60 – 80% when fresh)
Two major factors, that is the moisture content of the product when it comes from the field and the relative humidity of the outside air during the storage period, determine the choice for the best storage.
2.0 Objectives
At the end of this unit you should be able to:
Describe the different harvesting methods for different crops
Explain the harvesting methods for cereals
Understand how to harvest vegetables
Describe the harvesting methods for tree crops
Explain the harvesting methods for roots and tubers
3.0 Methods of Crop Storage
Insects and moulds impair the quality of grain directly by their feeding and development, and indirectly through generation of heat and moisture. High temperatures and moistures favour development of insects and moulds. Development of insects is limited by temperatures below 15°C, and by moistures below 9% in cereal grains. Development of moulds is limited byhigh temperature. High moisture and high temperature are the most significant factors affecting grain
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quality in storage. Each can cause rapid decline in germination, malting quality, baking quality, colour, oil composition, and many other quality characteristics.
Spraying with insecticides or fumigating minimises insect problems but leaves chemical residues in grain, which break down with time. Presence of residues, and their concentration, affects acceptability of the grain to markets. Some markets prefer grain without residues. Grain buyers will not knowingly accept grain treated at rates higher than those specified on the label, or within the specified withholding period.
3.1Cereals and pulses
3.1.1Conditions for storage
When dried to moisture contents below the safe moisture level, cerealsand pulses can be stored for periods of a year or more under a widerange of temperatures, provided that during storage the moisture leveldoes not rise, and precautions against insects are taken; insects maystill develop at a relative humidity of approximately 35% and temperaturesof around 15°C
Table 3.1.1: Safe moisture content for any particular grain may vary slightly depending on the variety (valid for temperatures up to valid for temperatures up to about 27 °C. Higher
temperature
Product Safe moisture contents %
Cereals Maize threshed yellow 13
Maize threshed white 13.5
Maize flour 11.5
Paddy rice 14.0
Husked brown rice 12.0
Sorghum 13.5
Millet 15.0
Wheat 13.5
Wheat flour 12.0
Pulses White and kidney bean broad 15
Cowpea 15
Lentil, pea 14
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The safe moisture content for any particular grain may vary slightlydepending on the variety.
The mentioned safe moisture contents arevalid for temperatures up to about 27 °C. Higher temperatures require lower moisture content maxima.
3.1.2Methods of Crop Storage
The following two factors determine the choice for the best storagemethod:
- the moisture content of the product when it comes from the field - the relative humidity of the outside air during the storage period (a) Temporary Storage Methods
Such methods are quite often associated with the drying of the crop, and are primarily intended to serve this purpose. They assume the function of storage only if the grain is kept in place beyond the drying period.
(i)Aerial Storage
Maize cobs, sorghum or millet panicles are sometimes tied in bundles, which are then suspended from tree branches, posts, or tight lines, on or inside the house. This precarious method of storage is not suitable for very small or very large quantities and does not provide protection against the weather (if outside), insects, rodents, or thieves.
(ii)Storage on the ground, or on drying floors
This method can only be provisional since the grain is exposed to all pests, including domestic animals, and the weather. Usually it is resorted to only if the producer is compelled to attend to some other task, or lacks means for transporting the grain to the homestead.
(iii)Open Timber Platforms
A platform consists essentially of a number of relatively straight poles laid horizontally on a series of upright posts. If the platform is constructed inside a building, it may be raised just 35-40 cm above ground level to facilitate cleaning and inspection. Platforms in the open may be raised
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at least 1 m above ground level. They are usually rectangular in shape, but circular or polygonal platforms are common in some countries.
Grain is stored on platforms in heaps, in woven baskets or in bags. In humid countries fires may be lit under elevated platforms, to dry the produce and deter insects or other pests.
Instead of being horizontal and flat, the platform may be conical in shape, the point at the bottom. Up to 3 m in diameter, such platforms facilitate drying because of their funnel shape: at the top they consist of a frame of horizontal poles which is square, circular or polygonal in shape, against which the timbers which form the cone rest; these timbers meet at the bottom on a wide central supporting post
Platforms with roofs (but no walls), of whatever shape or form, may be regarded as transitional types between temporary and long-term stores. In southern Benin, Togo and Ghana, for example, maize cobs in their sheaths are laid in layers on circular platforms with their tips pointing
inwards. The platforms are usually between 2 and 3 m in diameter, but some may be more than 6 m wide, with a maximum height of 2.5 m at the centre and 1.5 m at the periphery.