Cassava is a major staple in five provinces of Zambia: Northern, North-Western, Western, Luapula and Copperbelt. It is regarded as a ‘food security crop’ - it is not fertiliser dependent, can survive in poor soils and is drought resistant. Recent increases in the level of cassava production are seen largely as a response to the drought conditions of 1992/93. Producers are finding it to be a reliable alternative to maize, particularly in the face of difficulties in obtaining fertiliser. Despite the favourable characteristics of cassava and its importance as a staple in four provinces, the post-production operations do not favour large scale marketing of the crop. Most cassava produced in Mansa and Kaoma Districts is consumed locally although there are a few outlets to the Copperbelt, Mongu, Sesheke and Lusaka. For the time being prices for cassava remain low and unattractive.
It is generally accepted that, until recently, little attention has been paid to post-production operations for cassava. The Roots and Tubers Improvement Project base at the Mansa Technology Assessment Site (TAS) and two other donor- assisted projects in Luapula Province are now actively promoting improved production and/or post-production technologies for cassava. The objectives of the programmes include: increasing production, contributing to improved nutrition and food security and stimulating the marketing of cassava and cassava-based products. It has been suggested that the earlier neglect of cassava-based systems may, in part, be due to the fact that new technologies are invariably directed towards men, although it is the women who are responsible for all post-production operations for cassava. There has been an underlying feeling in the traditional communities that technical innovations will be physically inconvenient or too expensive for women.
It is widely recognised that the division of labour between men and women is unequal. Women appear to be overloaded and have difficulty in accomplishing all their tasks by the end of the day. In areas where cassava production dominates or where it is on the increase women are further overburdened. In Mansa District, studies by the Provincial Planning Unit (PPU) of Luapula Province show that, on average women spend 16 hours each day in work related activities, including home activities whereas men rarely spend more than 6 hours per day in work activities. A study by Due (1993) covering four provinces, reported a similar figure for female activities, while men were working for between 6 and 10 hours per day. The long working day for women is, therefore, a serious constraint to programmes aimed at increasing the production of cassava.
The generalised post-production system for cassava in Mansa District (Luapula Province) and Kaoma (Western Province) is illustrated in figure 2. The main difference between the two systems is that in Kaoma, the process begins with soaking of tubers, while in Mansa tubers are peeled after harvesting. In Kaoma the tubers are always soaked before peeling to protect the flesh of the tuber from contamination or to discourage domestic animals from eating the tubers (unpeeled tuber are less
Figure 2: Flow diagram of alternative methods for processing cassava into meal in rural Zambia
Cassava tubers are harvested as required after one or two years. In the third year all plants are uprooted, usually during the rainy season, when soils are soft. Most producers, especially in Mansa District had three fields with cassava at different stages of development. Those with only one field with cassava of mixed ages (mostly in Kaoma District) are considered to be food insecure.
Generally there are no technical difficulties in harvesting of cassava. However, women are largely responsible for this task and those in Mansa District especially, complain that they have to walk long distances (7-10km) to the cassava fields. Over time, fields have been established further away from the villages as soils are worked out through continuous cropping, because of damage to plants by domestic animals or an increase in theft. Fields could be re-established close to the village if more attention was paid to improving cultivation practices such as crop rotation and manuring and if arrangements were made for separate grazing areas for domestic animals.
Once harvested, cassava tubers begin to deteriorate rapidly, often within two days, due to enzymic changes and this is indicated by decaying tissues and discoloration (brown to darkish-blue) and streaking of the tubers. Such tubers are no longer fit for consumption nor industrial processing. If tubers are left in the ground beyond maturity, the starch content increases to a stage where lignification sets in so that tubers become tough, fibrous and woody. Cassava is therefore processed soon after harvest and then preserved dry as whole tubers, chips, slices or milled product.
Soaking is a primary step in the processing of tubers since it removes bitterness, improves flavour and softens the tubers for subsequent grinding or pounding. Of these factors, removal of the bitterness is regarded as the most important. The bitter constituents of cassava (cyanogenic glucosides) break down into toxic hydrocyanic acid and other by-products through enzymic hydrolysis and soaking renders the tubers non-toxic.
Although soaking is essential the process is time consuming and is affected by prevailing weather conditions. Longer soaking is required in the cold season 7-10 days compared to 2-3 days in the warm season.
The cassava breeding programme of the RTIP at Mansa TAS has considered the problem of high HCN levels. New varieties having a lower HCN content have been identified, especially for introduction to areas of the country where cassava production is less common (e.g. Southern Province). However, it was established that this was not a major concern since the HCN is readily removed in the routine soaking process.
Tubers are always peeled with a knife. Peeling in the dry season is more difficult because the skin adheres more strongly to the dry flesh of the tuber and loss of dry matter is high. Local varieties with short, crooked tubers are more difficult to peel than the straighter tubers of improved varieties. This post-production problem has also been considered by the RTIP cassava breeders. The aim of the breeding programme is not only to produce roots of a good size (increase in available food) but also to produce tubers with large, straight roots which are quicker and easier to peel and process than the short twisted roots of the local varieties. The programme is also beginning to release faster maturing varieties which reach maturity in eighteen months instead of the usual three years. There is already much interest in these varieties and the programme has established a number of multiplication sites to cope with the increased demand.
Traditionally, cassava is dried by spreading whole, sliced or pounded tubers in the sun although during the rainy season or periods of cold weather, the cassava may be dried over a fire. Sun drying in the dry season usually takes two to three days but in the rainy season the drying period may extend to over a week. Under these circumstances households may face real hunger through not being able to process the cassava and especially as alternative supplies of maize will normally have been exhausted. Individual farmers and a women’s group in Mansa said that they often faced difficulty in drying cassava in the rainy season and as a coping strategy only one meal per day was taken during this period. Some respondents said that, given enough family or shared labour they are able to dry larger quantities of cassava before the onset of the rains to alleviate the difficulties of drying in the rainy season. However, others do not have the time nor labour to do this. Some households who dried larger quantities of cassava before the start of the rains commented that there is a temptation to draw heavily on this reserve so supplies were exhausted long before the end of the rainy season.
The post-harvest technology section of the RTIP at Mansa TAS has recently developed a 25kg capacity drier, which is undergoing the first trials. It consists of a square drying chamber constructed from bricks and mortar with a metal sheet in the base to prevent smoke from the fire immediately below from contaminating the drying produce. Cassava is placed on trays mounted on a series of racks within the drying chamber. Construction costs are around K150,000 - K200,000 for bricks, cement, wire mesh and timber for drying trays, and the metal sheet. It is estimated that the cost could be reduced by using trays made from bamboo and reed mats and a cheaper alternative might be to use mud-plastered clay bricks rather than burnt bricks. The main cost component will be the metal sheet, which, it is acknowledged may be difficult to find away from the major towns. The feasibility of constructing and operating a mud brick drier is yet to be investigated. However, preliminary tests have shown that during the rainy season the drying time can be reduced from over a week to 1-2 days depending on the size of the pieces of cassava. Moreover, farmers invited to participate in the evaluation of the drier are showing a keen interest in the technology. A potential drawback might be the cost and possibly a shortage of firewood and in deforested areas this post-harvest technology may introduce a new environmental problem. Possible alternative sources of fuel have not been investigated.
In Mansa District there are two approaches to the soaking and drying of cassava depending on the need for long term storage : (i) peeling, soaking, drying, and (ii) peeling, drying, soaking, drying. The first method results in a softer product, relatively easy to pound and which can be stored for no more than about one month, because it is susceptible to insect attack. Cassava processed by the second method is reportedly much harder and therefore difficult to pound by hand, but is preferred for longer term storage as it is less susceptible to insect attack. Producers stated that cassava processed in this way can normally be stored safely for 3-4 months, although towards the end of this period some insect attack can be expected.
Storage of cassava is usually in the form of dried whole tubers, chips or pieces in bags or in loose piles in the roof space of the house.
The introduction of the Larger Grain Borer to Mansa District poses a serious threat to stored dry cassava. There is strong evidence from work in Ghana and Togo to show that LGB frequently attacks cassava during the drying stage. LGB has recently been caught in flight traps in Mansa town but, as yet, extension workers are not alerting producers to the potential problems posed by this new pest.
Traditionally, in the rural areas, cassava is pounded using a pestle and mortar but access to hammermills for cassava processing is now increasing, particularly in Mansa District (and in Luapula Province generally) and in Kaoma.
Although the use of hammermills relieves the drudgery of hand pounding consumers in Kaoma and Mansa considered the milled flour to be too fine and that a greater volume was required to prepare good nshima. Some also considered the taste of nshima prepared from milled flour to be inferior to that from hand pounded flour. Hammermill operators in Kaoma and Mansa confirmed that the milled flour was very fine and that some was lost in the dust created during the milling process. The flour also tends to block the sieve although work carried out by the RTIP in Mansa has demonstrated that the difficulty can be resolved by fitting a sieve of a different size. Even so, some millers consider it inconvenient to change the sieve according to the product to be milled, and one farmer/miller refuses to mill cassava. Notwithstanding these difficulties some hammermill operators in Mansa and Kaoma are considering buying or even producing cassava (and/or maize) for commercial milling as a means of improving the profitability of their enterprise and it is likely that such entrepreneurs would respond to consumer demand and come to some arrangement about changing sieves according to product. As long as the flour produced finds wide acceptance amongst consumers this change could further relieve women of the task of hand pounding. Moreover, commercially-milled cassava flour, if available during the rainy season could go some way to relieving some of the hardship felt by those who face difficulty in drying cassava.
The post-harvest technology section of the RTIP is developing new cassava flour-based products such as biscuits and sweet cakes. The trials are at an early stage and only a limited number of field demonstrations have been undertaken. It is reported that despite the early interest shown mainly by women, but also a few men, there has been little uptake. During the course of interviews with farmers in Mansa district one farmer/hammermill operator who had attended a demonstration session indicated that he had produced a small quantity of sweet cakes which had been sold locally in the village and he felt that this might be a worthwhile income-generating activity.
6.6.2 Chipping And Grating Machines
The post-harvest technology section of the RTIP has received some demonstration chipping and grating machines from IITA, Nigeria. Trials with these machines are just beginning. Preliminary investigations indicate that they can be produced locally at a cost of around K200,000. It has been demonstrated that the soaking time for cassava can be reduced to 1-2 days if tubers are first processed into chips. Moreover, these chips will dry much faster than hand-sliced pieces of cassava. Less work has been done with the grating machine, however, consideration is being given to incorporating grated cassava into baby weaning foods. None of these operations has yet been costed.