Chapter 5 Socio-economic importance of rapid post-harvest deterioration of cassava: quantitative and qualitative losses

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Physical post-harvest loss
Qualitative post-harvest loss
Implications for production
Implications for marketing
Implications for processing
Implications for consumption
Conclusions and future prospects

The rapid post-harvest deterioration of cassava restricts the storage potential of the fresh root to a few days. In addition to direct physical loss of the crop, postharvest deterioration causes a reduction in root quality, which leads to price discounts and contributes to economic losses. This chapter examines the socioeconomic implications of post-harvest deterioration on production' marketing, processing and consumption of cassava. The numerous strategies developed by farmers, traders, processors and consumers to deal with the limited storage potential of cassava are reviewed.

Physical post-harvest loss

Although rapid deterioration of freshly harvested cassava is considered an important factor in poet-harvest studies, little reliable information is available on loss figures. In some documents these figures seem to be only gross estimates based on anecdotal evidence and frequently the terms waste and loss are used without clear distinction. The term loss will be used throughout this chapter since waste can be considered a voluntary disposal of unwanted material such as peel.

Widely differing levels of post-harvest losses have been obtained in studies on cassava production and use in Asia conducted by CIAT in collaboration with national programmes (CIAT, 1987). The loss figures given were generally established on a macrolevel and do not indicate the cause of loss. The lossfigure estimates were in the range of 10 to 12 percent in India (Kerala and Tamil Nadu States), 5.3 percent for the whole of Indonesia, 6.2 percent for Java and 3 percent elsewhere. In Indonesia, however, component losses were assessed as 8 percent for marketed cassava and 15 percent for gaplek (large pieces of dried cassava).

Loss estimates for China based on FAO figures, which have been used for every year from 1961 to 1983, are 3 percent. The only figures available for Thailand (the world's leading exporter of cassava products) are for the exports of cassava products for animal feed; for Malaysia no loss figures are available. In the Philippines loss and animal feed figures are reported together.

A survey of consumer purchasing habits of fresh cassava and other starchy staples, undertaken in the Atlantic coast region of Colombia (CIAT, 1983), provided the following loss estimate figures: metropolitan urban areas 15 percent, intermediate urban areas 5 percent and rural areas 5 percent. Another simultaneous survey of market agents in the same area showed that deterioration accounted for 14 percent of the costs of the total marketing margin. A study on cassava commercialization in Paraguay in 1987 showed that during marketing about 15 percent of the roots were affected by deterioration, but only about 0.5 percent were completely lost (Cassava Newsletter, 1991).

FAO data for 1985 estimate that post-harvest loss for all root crops in Ghana are of the order of 15 to 30 percent and that post-harvest loss of cassava in the Côte d'Ivoire is 27 percent. However, a recent- survey in Ghana indicated low levels of physical post-harvest loss of cassava and estimated losses unlikely to exceed 5 percent (Rickard, Wheatley and Gilling, 1992).

The above figures focus on physical post-harvest losses which represent a direct financial loss to the producer, trader, processor or consumer. National loss figures usually do not indicate at which stage of the marketing chain the losses occurred. In addition, available data often do not differentiate between post-harvest deterioration of fresh roots and loss of processed products. The exact value of the loss is therefore difficult to calculate.

TABLE 8 Estimates of discounts for old cassava

Source: Rickard Wheatley and Gilling. 1992.
Note: ¹ Prices are per hag of cassava However, prices of old and fresh produce should only be compared for one market since the size of hags can vary considerably (from 50 to 1(8) kg) depending on the location of the market.

Qualitative post-harvest loss

According to studies carried out in West Africa, post-harvest deterioration of cassava causes a reduction in root quality which can result in roots being sold at a discount price. Two cases of discount have been distinguished. A lower price is commanded by old cassava in comparison to fresh roots and a price difference exists between fresh roots and cassava sold in a processed form at a lower price (e.g. fermented or dried).

It is often difficult to distinguish between the two kinds of qualitative loss since old roots can be sold both for direct consumption and for processing. The discount depends on factors such as post-harvest age, seasonality, cassava variety, supply and demand of fresh and processed cassava and storage facilities.

In the case of Ghana, it has been suggested that the financial post-harvest loss due to quality price reductions is greater than that caused by physical loss. However, it is difficult to estimate the amount of cassava that is sold at a lower price (Rickard, Wheatley and Gilling, 1992). Discounts commanded by old cassava roots can vary in Ghanaian markets according to location of the market and position of the intermediary within the marketing chain (Table 8).

In Ghana cassava which has visible signs of deterioration is not used for fufu production but is hand-peeled, chipped and sun-dried to produce kokonté. Although this is a time-consuming and arduous process the price of kokonté is low compared to fresh cassava. Over the period 1989 to 1991, the discount per kilogram applicable for cassava sold for kokonté has ranged from a negative 7 cedis in Accra rural markets in July 1991, to almost 80 cedis in Accra urban and Ashanti rural markets in September 1990. In 1991 the average retail price for fresh cassava in Ghana was about 80 cedis per kilogram me .

Implications for production

Over two-thirds of Ghanaian farmers interviewed during a recent survey said that post-harvest loss is a major risk factor in the production of cassava (NRI, 1992; COSCA Phase 1). Thus, although there are many positive factors that make cassava a well-adapted crop for small-scale agriculture in developing countries, rapid post-harvest deterioration of the fresh roots is a disadvantage that the farmers have to take into account. However, the rapid post-harvest perishability of cassava might be a major factor leading to comparative advantages for small-scale production linked to small-scale processing units.

Traditional approaches to rapid post-harvest deterioration have been developed by producers. A common way of avoiding loss is to leave the roots in the soil past the period of optimal root development, until they can be immediately consumed, processed or marketed. The disadvantages of this practice are that land is occupied and thus unavailable for further agricultural production (opportunity cost of land), roots lose some of their starch content, palatability declines as roots become more fibrous (Rickard and Coursey, 1981) and cooking times increase (Wheatley and Gomez, 1985). In Africa, there also exist a number of traditional systems involving cassava storage in pits or clamps. The use of these rudimentary techniques is not widespread as they are considered rather labour intensive and are not always entirely effective. Storage of cassava roots under moist conditions, as encountered in soil reburial methods, can promote the healing of wounds (see Chapter Two) in roots damaged at harvest.

Implications for marketing

Harvested cassava roots that are not kept under conditions favourable for wound healing/curing (25 to 35°C, 85 to 95 percent RH) usually become unacceptable for human consumption within two to three days of harvest. This fact conditions the marketing of this root crop.

Fresh cassava roots are traditionally marketed without post-harvest treatment or protection and therefore have to reach the consumer within a very short time before deterioration becomes visible (Janssen and Wheatley, 1985). A close integration of producer, intermediary, wholesaler, retailer and consumer becomes necessary to guarantee the rapid transfer of the produce from producer to consumer. This highly integrated marketing channel serves to prevent traders from being left with unsold, perishable produce. The result is a reverse marketing integration assuring the flow of information between consumers and producers. Often, traders arrange purchase and sale of their produce in advance to minimize their risk. Cassava is also frequently purchased in the ground and traders supply their own labour to harvest the crop when required.

In addition, the quantities handled by cassava traders are usually low. Thus, retailers buy and sell limited volumes in order to assure a rapid turnover of the produce. Janssen and Wheatley ( 1985) observed that cassava retailers in the Atlantic coast region of Colombia trade only about 50 kg of roots per day. However, deterioration still presents a serious problem to Colombian traders; 31 percent of rural assembly agents, 70 percent of wholesalers/distributors and 66 percent of retailers reported to have frequent problems with deterioration of roots (CIAT, 1988). The negative effects of the rapid deterioration of fresh roots lead to high marketing margins.

Cassava has a marketing margin of approximately US$0.30 per kilogram which corresponds to 60 percent or more of the crop's final retail price (Janssen and Wheatley, 1985).

In Ghana cassava marketing chains have evolved to cope with the perishability of the root. Rapid marketing is assured through a wide range of operators including producers, itinerant traders, transporters, intermediaries, market traders and market chiefs. Sometimes it is not possible to distinguish between the different operators because some of them fulfil several functions within the marketing chain (Rickard, Wheatley and Gilling, 1992). Operators such as farmers, traders and consumers are often connected through complex systems of information flow, credit, transport, etc. Assemblers will sometimes buy standing crops in order to increase flexibility in timing fresh root deliveries to urban markets. It was noted in Ghana that woven polypropylene sacks were often used when transporting cassava over long distances, whereas jute sacks were commonly used for short distance transportation. It was also reported that cassava roots tended to have a longer storage potential when transported in polypropylene sacks.

Infrastructure and distance to the final markets play a critical role in the distribution and marketing of cassava. Poor roads, inappropriate means of transport and a badly organized distribution system are factors leading to elevated marketing costs, which in turn result in high consumer prices. This particularly discourages consumption of cassava in urban areas where the roots have to compete with other foodstuffs. Fresh cassava can only be marketed over significant distances if there is a well-developed road system ensuring that the period of transportation can be kept to a minimum and the roots delivered when they are still fresh. Kinshasa, which is the major centre of consumption of the Zairian economy, is mainly supplied with fresh cassava roots from the BasZaire region with which it has become well connected in recent years through various road building projects.

The degree of market integration needs to be higher for the supply of large urban centres and requires well organized transport over a long distance. In order to improve the existing cassava marketing system in Colombia, CIAT and NRI have developed a simple method to extend storability of fresh cassava. The technology is based on the storage of fungicide treated fresh roots in polyethelene bags (see Introduction).

The processing of the highly perishable and bulky cassava roots into a storable and stable commodity, such as gaplek in Indonesia, facilitates more efficient marketing. This is reflected through cassava prices which are linked spatially across the country and vertically through the different forms of use.

Implications for processing

Avoidance of rapid post-harvest deterioration and reduction of cyanide levels are traditionally the main reasons for processing cassava into different food products. As almost every cassava-growing region in the world has developed its own traditional products there are a large number of foodstuffs based on cassava. Results of the COSCA Phase I survey in Africa show that sweet cassava varieties and non-bitter varieties are more commonly grown and used for processing (NRI, 1992).

Traditional technologies are well adapted to processing cassava into a number of final products characterized by extended shelf-life (Miche, 1984). Traditional processing methods are often very time-consuming and laborious; this is especially the case in Africa where the roots are processed into local products such as gari.

Cassava starch is produced for both human consumption and industrial use. In Latin America the cassava starch industry is reported to experience several limitations, including low availability of fresh roots, lack of capital, difficult access to credit, poor management and poor starch extraction efficiency (Chuzel, 1991).

The sedimentation of starch from deteriorating cassava is considered by processors in Latin America to be less efficient than from fresh roots. These observations have not been substantiated by reported technical studies but recent results from CIAT (F. Alverez, private communication) have shown that starch extraction rates were significantly affected by post-harvest deterioration. The possible influence of deterioration on starch production is of importance considering the significant role of starch in the cassava economy of a country such as Indonesia. In 1978 about one-third of all the cassava utilized in Indonesia went into starch production (CIAT, 1987).

In Thailand the cassava industry experienced a pattern of growth in marked contrast to that of other agricultural commodities, especially the grains. To avoid losses from root deterioration, cassava has to be processed very close to the production areas and processors have to ensure a daily supply of raw material. In the case of cassava the expansion in root production and processing has been based on linking small-scale producers to relatively small-scale processing capacity. Decentralized, small-scale processing was an important strategy to resolve the problem of minimizing transport costs and to avoid postharvest deterioration of a bulky, low value raw material (CIAT, 1987). Fresh roots are generally processed on the day they arrive at the factory and it is rare to find industries that have storage facilities (Thanh, 1974).

Cassava processing industries that use dried raw material, such as gaplek for chip or pellet production, do not depend on rapid processing of the roots since the dried raw material can be stored for several months. Seasonal supply shortages of cassava can be avoided by drying peeled pieces of roots immediately after harvest and storing them on-farm or at the site of the processing industry until required (Falcon et al., 1984).

In Indonesia, although cassava production does not require large labour inputs, it does generate significant employment in processing and distribution. Similar observations have been made in Viet Nam, where income was higher in villages with small-scale cassava and other root crops industries compared to villages without these industries (Bottema and Henry, 1991).

Implications for consumption

Cassava is one of the major subsistence crops produced in developing countries. In rural areas of many cassava growing countries the roots are mostly consumed fresh. As cassava harvesting can be staggered, rapid postharvest deterioration does not severely influence on-farm or village consumption.

In urban areas, unless motivated by economic considerations, consumers will not generally purchase old cassava roots (three to four days after harvest) as they are assumed to have deteriorated. To demonstrate the freshness of the produce retailers often take extreme measures. In Colombia, root freshness is demonstrated by cutting the roots to show undeteriorated internal tissue (Figure 19). In markets in Ghana it has been observed that market sellers deliberately wound certain parts of the roots to cause latex exudation which is produced only by fresh cassava. Both these activities severely reduce the storage potential of the damaged roots but allow retailers to demonstrate that their produce is fresh.

Cassava roots that exhibit visible symptoms of physiological deterioration are considered to have poor eating and processing quality. Although no survey work has been undertaken on this topic, the following observations have been made regarding cassava that has developed physiological deterioration (Rickard, Wheatley and Gilling, 1992; C.C. Wheatley, private communications):

• it takes longer to cook, has an unpleasant bitter flavour and an unattractive off colour;
• fulu processed in Ghana from deteriorating roots has a lower and less desirable elasticity than fufu prepared from fresh roots;
• cooked roots are difficult to pound;
• gari processed from deteriorating roots has lower and less desirable swelling properties than gari produced from fresh roots.

Market access is a crucial factor influencing cassava consumption in cities (CIAT, 1988). The extreme perishability of cassava severely limits consumers' ability to store fresh roots at home. This necessitates urban consumers making frequent journeys to local markets and outlets, which can be financially prohibitive. Ownership of refrigerators and freezers, which can be used to store fresh roots, has been found to lead to increased cassava consumption. However, families where the principal shopper is employed tend to consume smaller quantities of cassava (CIAT, 1988). The urban consumer regards purchase of cassava as involving considerable effort and risk. Cereals in the form of wheat flour, rice and maize are more convenient, storable foodstuffs compared to fresh cassava roots. Thus, while cassava is well adapted for rural consumption, other major foodstuffs are preferred in urban areas.

The combination of high marketing costs for cassava and market interventions, such as subsidized cereal prices (Lynam, 1991; Dendy and Trotter, 1988), often leads to high relative cassava prices. This can negatively affect urban demand because of the significant cross-price elasticities between cassava and major grains.

Urbanization leads not only to reduced demand for perishable foods, such as fresh cassava, but also to an increase in the consumption of processed foods. In many cassava producing countries the roots are traditionally processed into a broad range of storable products. However, traditionally dried products such as kokonté or gaplek are often considered as inferior foods that are only consumed by the poor. Therefore these inexpensive and easy-to-store products are characterized by negative income elasticities for higher income brackets.

Krupuk, a cracker based on cassava starch and widely consumed in Indonesia, has income elasticities of 1.56 for rural consumers and 1.35 for urban consumers (Falcon et al., 1984). This indicates potential markets for certain processed cassava products that have a positive image among consumer groups. Newly developed "modern" cassava products are apparently more acceptable to urban consumers. Food industry trials in Colombia have shown that wheat flour can be successfully substituted by cassava flour in the production of biscuits, cookies, cakes, pastas, soups and processed meat (Wheatley and Best, 1991).

Demand for fresh cassava in urban areas depends on factors such as relative price of the product, storability, convenience and market access.

TABLE 9 Strategies to prevent rapid post-harvest deterioration of cassava roots.

However, it seems that increased urban consumption can only be achieved through an improved product differentiation and market segmentation which include processed foods targeted at all urban consumer groups.

Conclusions and future prospects

Producers, traders, processors and consumers have all developed strategies, as outlined in Table 9, to prevent post-harvest losses of cassava. However, quantitative and qualitative loss estimates can often still be high. The production advantages of cassava (see Introduction), together with its being one of the principal crops grown by small farmers in marginal areas justify its development as an urban food. New technologies to improve the marketing and facilitate the processing of fresh cassava will help to stabilize and increase the level of urban consumption and the income generation potential of small-scale farmers, particularly in marginal areas. However, the successful competition of cassava in the future with other carbohydrate sources will also depend on certain other conditions, such as the reduction of market distortions that favour imports or other locally produced staple crops. Future efforts to overcome rapid post-harvest deterioration of cassava should take into account the needs and constraints of the farmers, traders and processors and also the preferences of the consumer.

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