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From time to time, people feel called upon to criticize the lack of solid results in the sphere of post-harvest losses. While these losses are undoubtedly of major importance, issue must be taken with the style of such criticisms, which are too often based on incomplete or poorly understood data, or mean that certain pre-harvest shortcomings are conveniently ignored.

In view of the questions asked and the articles and books dealing with the subject, it therefore seemed vital to challenge accepted ideas and highlight the complexity of the issues involved in post-harvest losses.

First of all, people too often forget that loss, in the sense of decline and decay, is an integral part of the life cycle of both individuals and societies. At a time when humanity is becoming more aware of its collective responsibility toward the environment, it would be paradoxical if it forgot that food is a living thing, which evolves within a complex of factors, not only biological and climatic, but also human, i.e. economic, social, cultural and political.

This does not mean that differences in climate should be ignored, for they constitute major constraints over which we have little control. Unlike developed countries which are mostly situated in temperate zones, developing countries are in tropical zones and are exposed either to one short rainy season, or to frequent and sometimes violent rainfall and high humidity. Such conditions have major consequences for post-harvest systems, especially the storage stage. The combination of heat (around 30°C) and ambient humidity (between 70 and 90 percent) fosters reproduction of the main insect pests, which multiply fast (up to 50 times in a month for the bean-seed beetle and 70 times for the Tribolium or flour beetle), as well as micro-organisms such as yeasts and moulds. Respiration is also speeded up, so that nutrient reserves suffer and premature germination can even begin, thereby compromising the preservation and future use of produce.

Weather conditions alone cannot explain the infestation and proliferation of parasites and pests in foodstuffs. International trade also plays a part. People often cite the case of rats which travel aboard cargo-ships and then escape when the ship docks finding their way into warehouses. However, insects also migrate from one continent to another and some of these "hidden" migrations have had disastrous consequences, such as the recent case of the larger grain borer (Prostephanus truncatus), which is discussed later. There is a danger that the enormous increase in intercontinental travel and trade of every kind can only increase this kind of risk.*

The effects of new seed varieties developed in research centres and laboratories should also be taken into account. They not only require more investments and various products (seeds, irrigation, fertilization, phyto-sanitary treatments) involved in cultivation and production, but are also more vulnerable to the depredations of pests and to damage in post-harvest handling. Agricultural research, with the help of genetics, has given priority to plant productivity, but this quantitative concern has entailed new difficulties in connection with harvesting (bent or flattened stalks, tough stalks, need for artificial drying, etc.), threshing (breakages, grain fragility) and especially preservation (greater sensitivity to atmospheric fluctuations, pest attacks, etc.). Successful adaptations are not produced overnight and are never made without the support and cooperation of growers.

Sustainability through repeated cycles of germination and ripening is vital, although there are contradictions here too. At a time when sustainable farming practices are the centre of attention, the world of economics is dominated by a concern for short-term and preferably, maximum yields. This does not sit well with farming, which does not generate high short-term profits but is oriented more toward long-term results.

Those who are disturbed by the level of losses often base their reasoning on economic calculations showing the profits possible if these losses were eliminated, without taking the trouble to examine the costs of arriving at such a result. Taking harvesting as an example, a combine-harvester can easily be replaced by an army of harvesters who would gather each ear by hand, but at what cost? Would such an effort be considered free and for whom? Peasant farmers' lives are far from easy and it is hard to imagine that they are squandering their harvests unnecessarily. Another point often overlooked is the effects of losses on production. A 20 percent harvest loss means that 20 percent of the elements necessary for production have also been lost, whether labour, inputs, water or time. This point is very seldom mentioned in estimates of losses, at a time when maximum efficiency is sought and available arable land and water are shrinking.

Unreliable data and methodological problem

Taken together with the lack of certainty on the source of figures, such oversights and omissions are puzzling, but they do in fact reflect the more general problem of the reliability of available information. The quest for greater rigour and consistency raises a methodological problem. In the first place, the basis for any analysis has to be defined. What operations are included in the post-harvest system? What is its starting point and where does it end? On what basis are losses to be calculated, amounts harvested, hoped for, or estimated? Do we work from the theoretical or recorded yield per hectare? Are post-harvest operations part of the production cycle, or should they be considered part of the processing and distribution sector?

All too often, activities tend to stop when the product is ripe, with a marketing or processing component tacked on as an after-thought, with no concern over continuity and consistency in approach. What happens between the field and the trader's shop or the processing plant? At what stage are rights of ownership transferred from one operator to the next? How should the added value be apportioned?

An overall understanding of the workings of the post-harvest system is clearly needed and a number of questions still requires answers. It therefore seems best to review the problem as a whole and work out a methodology that can lead to solutions. This approach would have a different aim from the majority of surveys and studies carried out to date. Rather than focusing on the observation and calculation of losses in each operation, it would give priority to identifying the factors responsible for these losses through all the phases of the post-harvest chain. It would be descriptive, analytic and explanatory, rather than quantitative and hence, more in keeping with both the spirit and understanding of a complex whole in which technological, sociological and economic elements are closely interwoven. This would provide a more credible and solid basis for developing possible technical improvements (human position and intervention, equipment, structures, materials, etc.) and introducing effective innovations.

While awaiting these changes, small producers will continue to protect their harvests and preserve their produce as best they can, slowly and cautiously adopting new methods, as they have done throughout the centuries, carefully refining techniques and systems to meet their own specific needs. Traditional granaries are a good example: genuine models of local architecture and functional craftsmanship, their effectiveness has been questioned in recent years. Developers have generally tended to take this latter view, believing they were doing the right thing in proposing only systems based on those of developed countries, without trying to prepare the ground for progressive incorporation of new techniques. They were certainly unaware of what Martin Greeley, a man with an excellent understanding of Asian cultures and peoples, was writing at the time: "It is simply unreasonable that farmers who have developed their post-harvest system over centuries should be suffering food losses of 20 percent or more" (Cérès, FAO, 1982). Such an observation should be borne in mind when planning and carrying out any action aimed at developing the rural and agricultural sector.

Food supplies for both animals and human beings are being put at risk as people blindly ignore facts and pursue a competitive, productivity-centred line of economic reasoning. Moreover, while consumption is rapidly growing, in many countries more and more farmers are abandoning the land. There are clear grounds for admitting that the old peasant farmers had and still have, a finely honed sense of economics when they fed their food waste and produce, unfit for their own consumption, to their livestock. This was their way of building up capital on the hoof, as well as ensuring themselves a liquid reserve and a prized food for special occasions. Not only were post-harvest losses limited, but anything that could not be eaten was put to some other use, thus providing some guarantee against emergencies and unforeseen events.

* Here we would recall another bio-environmental difference between temperate and tropical climates: in the former, insect pests such as the weevil and the bean-seed beetle can survive only in their preferred environment, but in the latter they can survive independently of their preferred diet (the larger grain borer is an example here).

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