2.3.3 Improved yam storage in Benin

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Two storage structures of about three tonnes capacity, made from local materials, have been evaluated under the FAO project "Decentralized Storage Systems".

Technical Description

• The raised hut, a structure mounted on poles fitted with anti-rat shields (Figure 2.2).
  
• The cellar-hut, a trench 4m x 2m x 1.8m deep (figure 2.3). The mud walls are 60cm outside the edges of the trench, thus providing a space for movement. Wooden planks forming a duckboard placed in the bottom of the excavation and covered with straw insure good insulation of the tubers from the soil. Alleys arranged between the walls of the trench and the stacks of yams (30cm) and between the stacks themselves (50cm) facilitate air circulation and inspection.
• The yams stored in both these structures were treated with Koufla(1) at a rate of 2.5kg per tonne of tubers.

Figure 2.2 - The raised hut (Source: Fiagan, 1994)

Figure 2.3 - The cellar hut (Source: Fiagan, 1994)

Results

The improved method was compared with traditional storage (stacks in a hut) in two ecological zones in Benin, using early varieties (Kpounan/Labako) and late varieties (Gnidou). Quantitative losses were measured together with the quality of the tubers conserved and the value benefits obtained after 120 days of storage (Tables 2.3 and 2.4 below).

Table 2.3 - Percentage loss measured in Central Benin

Table 2.4 - Percentage loss measured in North Benin

The good results shown above confirm the value of improved storage structures. With respect to quality, the higher moisture content of the yams stored in the cellar hut improved the preparation of pounded yam and thus the appreciation of the consumers.

With respect to the economic results, the study showed that the producer obtained for the early varieties a benefit of 220% in value with the improved storage (against 44 % with traditional storage). However, with the late variety the benefit was the same whatever the type of storage. There is a risk that the cost of the improved storage together with the phytosanitary treatment, especially after the devaluation of the CFA Franc in January 1994, could prove to be a constraint to the development of this type of storage.

2.4 The potato

The production of potatoes in Sub-Saharan Africa is often limited to high altitudes, notably in Kenya, Burundi, Cameroon and Nigeria. Introduced to these regions relatively recently, potato cultivation is accompanied by only rudimentary storage structures. The potatoes are simply heaped on the ground in a store room. They are put in jute sacks for marketing.

In Cameroon, in the North Western Province the potato represents a cash crop for the women who produce almost 75% of national output, estimated at 35,000 tonnes. The price fluctuates with the season. At its lowest after the first harvest (July-August), it attains double or triple its initial value in late November - early December (12 to 15 weeks after harvest). The majority of producers do not benefit from this increase because they do not store their potatoes beyond two months. The quantitative and qualitative losses are due mainly to rodents, to the short dormant period of the varieties grown and to lack of ventilation. Losses reach 4.4% per month during storage from January to June (second crop potatoes) and 5.5% per month during storage from July to December (Toes, 1982).

The FAO/UNDP project in Cameroon entitled "Development of Post-Harvest Systems", has designed and promoted a small mud structure for storing about a tonne of potatoes (Figure 2.4).

Figure 2.4 - Mud-walled structure for potato storage (Source: Hunt, 1982)

Chapter 3: Techniques for threshing, shelling and parboiling grain

Maize shelling and the threshing of rice, millet and sorghum are post-harvest operations which consist of separating the grain from the ear. For all these cereals, the traditional manual method is still widely predominant for this operation (Figure 3.1).

3.1 The rice harvest

Experience in rice harvesting has been gained in two fields:

• Improvement of manual harvesting of rain-fed rice with the introduction of the Asian sickle in Gambia and Sierra Leone. The experiences mentioned below have been described by Manalili in "Introduction of the Asian Sickle".
• Mechanization of the harvest though the introduction of combine harvesters (Niger and Senegal River valleys) or motor-driven reapers (Madagascar project). A description of the acquired experiences through rice harvesting mechanization can be found in FAO Bulletin N° 109.

3.1.1 Observations on the traditional method

Rainfed rice or shallow-water rice is harvested manually by means of small knives, ear by ear, by women who gather them in sheaves (about 5kg of paddy) before transporting them to the homestead for storage. The harvest takes place at the beginning of the dry season. The method is slow and very laborious. Nevertheless, this method of selective harvesting appears adapted to unselected varieties of rain-fed rice where panicle maturity is spread over a period of time.

Irrigated rice is harvested in Gambia with a fairly heavy European type of sickle (figure 3.2). This operation is generally reserved for men and should be effected rapidly because irrigated rice reaches maturity just before the rainy season. It is thus necessary to harvest and dry it as rapidly as possible.

3.1.2 Introduction of the asian sickle

The post-harvest project fielded by FAO in Gambia (1992) introduced the Asian type of sickle and was directed to training artisanal iron-workers in order to promote the local manufacture of such sickles (figure 3.2).

The advantages of the Asian sickle are:

• Technical improvement: the sickle permits several stems to be cut at a time, close to the soil. The direction of cut and the shape of the teeth create a self-sharpening action for the sickle.
• Productivity gain: 122 hours/ha/person with a sickle compared with 721 hours/ha/person with traditional methods, or six times more labour required by the traditional method. This is a benefit in improved varieties (yield above 1.5T/ha, density above 200 plants/m²).
• Reduction of losses by shattering through completion of harvesting in the ideal period.

The disadvantages are:

• More difficult threshing and higher losses because of the greater length of straw. However, threshing in the field permits a reduction of losses during transport.
• Greater physical effort in a bent position while harvesting.
• Necessity to use varieties which ripen at the same time but which are not always available.

In conclusion, the introduction of the new type of sickle, where local culture permits it, improves productivity and indirectly reduces post-harvest losses.

Figure 3.2 - The three types of sickle used in Gambia

3.2 Rice threshing

In the case of rice (also of sorghum)² the traditional technique consists of beating sheaves of rice with a wooden flail on a roughly swept threshing yard. This leads to a mixture of rice with debris of varied origin, notably soil and small pebbles; even metallic debris. Winnowing does not remove such debris completely. This is the principal cause of wear of the mill huskers which are seldom provided with pre-cleaners. Moreover, late harvesting due to shortage of labour leads to direct losses from shattering and indirect losses through cracking of the grain.

Observing that poor threshing conditions are counter-productive from the point of view of milling and final quality of the rice, research and development bodies have worked on the design and dissemination of improved threshing technologies.

3.2.1 The threshing table

With the objective of facilitating the threshing of long strewed rice at the site of harvesting, an FAO project has introduced a modified version of the threshing table used in Asia, adapted to local conditions (Manalili, 1994). Threshing is effected by beating sheaves of rice against an interwoven grille of bars forming an inclined trellis (Figure 3. 3). This model was modified during the course of the project by lowering the table with respect to the ground and by using branches of neem and mangrove, more resistant to termites, for the bars of the grille. A more solid metallic model has also been constructed for irrigated rice.

The threshing table has an average capacity of 20.8kg/h/person or 41.6kg/h with two operators. Where yields are higher (3T/ha) capacity can be doubled to achieve 80.6kg/h with two people. Moreover, loss of unthreshed grain are less than 1%

It is estimated that the use of a threshing table can save US$3.71 per hectare on the basis of an hourly wage of US$0.17 found in that locality. Compared with the cost of acquiring the table (US$4 for the wooden model or US$17 for the metallic version) the saving appears profitable.

Figure 3.2 - The threshing table (Source: Manalili, 1994)

3.2.2 Motorized threshers

Development programmes in the post-harvest sector have sought to mechanize the rice threshing operation with two objectives: to increase capacity for post-harvest treatment in order to alleviate time constraints under double cropping systems and to promote local fabrication of equipment to reduce investment costs.

Table 3.1 below lists the threshing equipment introduced or evaluated under various projects in the FAO Prevention of Post-Harvest Loss Programme (Visser, 1993). Among these models, the Votex thresher is the one which has been most often tested and which is the objective of local artisanal manufacture in Senegal and Mali.

Table 3.1- Threshing equipment introduced or evaluated under various PFL projects

N.B. Yields indicated correspond to rice threshing; in certain cases threshers have been experimented with other products (Source: Visser, 1993)

3.2.3 The votex thresher

In this section the experience of the "Office du Niger" in Mali (rice growing region of 50,000 ha) is described. For more detailed information, see chapter 4 of FAO Bulletin N° 109.

History

In the mid-1980s rice was threshed by tractors-driven threshers. Problems of drainage of the paddy fields and management of equipment led to delays of up to six months. Charges imposed on the peasant farmers amounted to as much as 12% of the value of the product threshed. In 198384, portable threshers, developed and tested in Mali, were evaluated, and a programme of extension, of agricultural credit and of operator and mechanic training was initiated. By 1988, 500 Votex threshers had virtually replaced the old classic threshers managed by the Office du Niger (Touré and Wanders, 1994).

Technical Description

The Votex thresher is a simple machine; it only has one moving component, the toothed (or barred) drum of 400mm diameter (Figure 3.4). The drum and concave are mounted in a chassis to which are attached the transport rings. A hatch permits cleaning and adjustment. The drum is fitted with vanes and thus functions at the same time as a fan (initial cleaning), and 85 % of the threshed product is collected from below the thresher. A sheet placed behind the thresher collects the remaining 15 % of threshed grain. The rotational speed of the drum and the clearance between drum and concave are set to provide stronger threshing depending on the crop. The threshing capacity varies from 400 to more than 800kg/hour. This capacity permits in a two months threshing season about 60 - 100 hours work per thresher. Threshing requires a crew of 6 persons. Supplementary winnowing is generally carried out by women.

Advantages

Portable:
Small dimension and light weight (175kg)

Multi-functional:
Thorough threshing (minimum losses), facilitated product flow, initial cleaning.

Simple:
One moving part; two adjustments.

Robust:
Threshing teeth and fan blades in steel to resist abrasion from paddy.

Durable:
Threshing teeth need partial replacement once or twice per season (15,000FCFA). Concave needs replacement completely (100,000FCFA) or partially (25,000FCFA) after 3 or 4 seasons (1,000T of paddy). Drum and drum teeth need replacement completely after six seasons (1,500 T of paddy).

Contrary to the rejection suffered by the more imposing, classic threshers, this new VOTEX thresher which links ease of use to flexibility, has been rapidly accepted by the farmers because of its manifest advantages.

Figure 3.4 - The Votex Thresher (Source: Touré and Andraianarivelo, 1994, IRRI)

3.3 Parboiling rice

The fact that rice production in African countries is uncompetitive compared with Asian rice is explained largely by the cost of processing which is too high3. Milling efficiency does not exceed 60% and the proportion of broken grains (35-40%) is very high. As practiced in South East Asia, parboiling has spread very little in Africa, with the exception of Sierra Leone and Liberia. Up to 1990 in Cameroun all available parboiled rice was imported from Thailand.

3.3.1 Phases and advantages of parboiling

The phases are:

• Soaking in warm water (50-60°C) increases grain humidity (at least 30% moisture content) facilitating conversion of starch to gelatine.
• Steaming achieves a "gelatinization" temperature of 70°C. In the gelatinous starch all cracks disappear.
• Drying the parboiled paddy, after cooling for a short period in the shade, is effected by spreading the paddy in the sun. Once moisture content is lowered to 16% or 18% the product is covered for 2 to 4 hours (resting or tempering). Then drying is resumed until moisture content is lowered to 14%.

Parboiling is a steam treatment of paddy which alleviates the effects of poor drying (cracking) and improves yield quantitatively and qualitatively since the proportion of broken grains is reduced. (Diop and Wanzie, 1990). The cooking quality of parboiled rice is better because the grains stay firm and do not stick together. The rice is also more nutritious because the proteins and vitamins are diffused through the centre of the grain after parboiling. Lastly, parboiled rice stores better thanks to its greater hardness. Only its stronger flavour and yellowish colour could be disadvantages.

3.3.2 Experience of rice farmers in the north west of Cameroon

A parboiling technique was introduced based on a very simple method (Figures 3.5 and 3.6). A 200-litre metal drum is cut into two half drums. The upper half drum, the bottom of which is pierced with small holes, and which contains the paddy, is placed on top of the second half drum containing boiling water. A hearth of clay bricks minimises wood consumption (15kg of wood for 50kg of paddy).

Following this trial on a small scale, 25 % of rice marketed locally was parboiled; 55% was parboiled by the producers themselves, 45% was parboiled by small processing enterprises and one regional state enterprise (Diop and Wanzie, 1990).

Figure 3.5 - Equipment for parboiling based on metal half-drums

Figure 3.6 - Parboiling method with drums and perforated tubes

Above: Soaking in warm water
Below: Steaming the two batches

3.4 Improvement of methods of maize shelling

The traditional shelling technique found most often in Africa consists of using a stick to beat a sack full of dry maize cobs. This practice causes a relatively high level of cracking and consequently makes the grain vulnerable to insect attack. In several countries, where quantities are small, the women employ another method in which two cobs are rubbed together, causing the grains to fall. This method avoids cracking the grain but needs very dry cobs.

The introduction of a wooden sheller permitting manual shelling, cob by cob, has been tried in several African countries. This implement, of limited capacity better adapted to the shelling of small quantities for seed, has not been adopted by the people.

Mechanical, manually operated shellers have been introduced in the context of the fight against the Larger Grain Borer (Grand Capucin) to permit the grain to be stored and treated with insecticides. The operating principle of these machines consists of passing the cobs between two rotating toothed plates. Three or four operators are required and the output varies between 205 and 450kg/h.

Following the increase in quantity harvested and the need to use fan-assisted hot air dryers, the development of rental services for motorized shellers may be foreseen. In the design of development projects of this type it will be necessary to take into account the respective roles of men and women in the shelling operation.

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