Previous - Next
This is the old United Nations University website. Visit the new site at http://unu.edu
Post-harvest food losses in developing countries: A new study
Some of the world's harvests of food crops and food fish, inevitably, never reach what the technologists in the field of post-harvest food conservation call the food-preparation stages. Bad harvest timing, inefficient machinery, carelessness, rats, insects, moulds, bacteria, contaminants, heat, cold, moisture, and lack of moisture continue to cut into the harvests. The expert group that determined the priorities of the United Nations University's World Hunger Programme in 1975 concluded that the problem of post-harvest food conservation was not receiving sufficient attention from established international and bilateral agencies. They recommended that it be one of the three sub-programmes of the World Hunger Programme.
A new 215-page study, Post-harvest Food Losses in Developing Countries, just completed by a committee of the United States National Research Council, concludes that "post-harvest food losses are 'enormous'." Yet, the report says, "we do not ... know what proportion of the post-harvest losses it is technically or economically feasible to reduce. Nor will we be in a position to assess this until systematic, co-ordinated efforts to estimate and reduce losses are implemented at national, regional, and local levels over a wide area."
The committee found no typical figures for losses, but quoted 1977 Food and Agriculture Organization statistics showing wide ranges and high variability of estimates. Thus, one report of wheat loss by weight in India showed a range of 8 - 25 per cent, and another showed a range of 2 - 52 per cent. A range of wheat loss of 6 - 19 per cent by weight was reported for the Sudan, and a range of 15 - 20 per cent was shown for Brazil.
Experts in this kind of analysis cite minimum post-harvest losses of 10 per cent for durable crops and 20 per cent for non-grain staples, perishables, and fish, according to the committee's review. Using these rough guidelines, the committee calculated that "in developing countries a conservatively estimated minimum of 42 million metric tons of cereal grains and legumes were lost in 1976 ...."
The number becomes less abstract when considered in terms of equivalents noted by the committee: it is equivalent to slightly more than the annual cereal production of Indonesia and Thailand combined; it is equivalent to 95 per cent of Canada's annual cereal-grain production; it is equivalent to 60 per cent of the annual cereal-grain production of Africa; at a 250 kilogram-intake per person per year, "this tonnage would provide more than the annual minimum calorie requirements of 168 million people-twice the population of Pakistan, or a quarter of the population of India."
In the absence of evidence suggesting how and what part of such losses might be cut, the committee extrapolated from apparent loss-patterns and expected production trends and projected 1985 post-harvest food-losses to be, at minimum, 47,000,000 metric tons of durable crops, 60,000,000 metric tons of perishable crops, and 10,000,000 metric tons of fish. Fish were not figured in the earlier estimates, because they are so obviously perishable that small catches are assumed to be consumed locally and quickly; losses of fish became important in the projections as fishing enterprises increased in number and size.
Aggregate statistics of this sort tell why post-harvest losses ought to be curbed, and national post-harvest-loss estimates are needed to tell how much and what kind of governmental intervention ought to go into reducing these losses, but gathering such information should not become an end in itself, the committee said. The report urges that national programmes to reduce post-harvest losses integrate loss-reporting with efforts to halt these losses as they are discovered and with efforts to prevent their recurrence.
These losses do not seem to be concentrated at any single stage in the ground-to-cook-stove sequence; Southeast Asian rice-loss estimates quoted by the committee suggest a few per cent in immediate post-harvest handling, a few per cent in threshing, a few in drying, a few in storing, a few in milling, with the range of estimated loss for milling (2 - 10 per cent) a little higher than the range of estimated losses in preceding stages {between 1 or 2 and 6 or 7 per cent). With perishables-fruits and vegetables, for example- losses clearly relate more to the time after harvest. According to the committee, "losses frequently increase rapidly, often becoming total within weeks or even days."
This report characterizes post-harvest losses of durables, such as cereal grains, as serious, and it characterizes losses of perishables as even more so. "From the few figures available," losses of perishables "are clearly excessive, save in a few cases where the unit food value is relatively high and efficient handling and distribution systems operate," the committee reported. "The average minimum losses reported for roots and tubers and fruits and vegetables were 16 per cent and 21 per cent respectively; many more 'qualitative' references, not included here, indicate estimates of 40 - 50 per cent and above. The figures are hard to interpret. One can only conclude that losses are severe, that more critical work is required to obtain better estimates, and that, living standards slowly rise in developing countries, both government and private organizations will endeavour to improve the marketing process and the supply of higher quality perishables to the consumer."
Losses from physical, physiological, and pathological damage to perishables can be minimized by care in harvesting and by special treatment in storage, but economic obstacles may block such care and treatment, according to the committee. Deterioration of perishables can be the result of their own physiological processes, such as sprouting in roots and tubers, or it can be the result of attack by fungi or bacteria, with damage made more likely by lesions from careless harvesting. Low-cost cooling systems "offer the greatest possibility for extending the life of perishables and radically changing traditional handling limitations." Even slight reductions in temperature could make a big difference, big enough to make "this a priority area for research."
Causes of post harvest damage to durable food crops, including cereal grains, sometimes encompass pre-harvest factors. Traditional grain varieties, having survived storage for use in subsequent planting, might be well adapted to both the growing environment and post-harvest handling; their characteristics may include lower moisture content in ripe grain which would dry more readily, and thicker seed coat which would be harder for rodents and insects to penetrate. In contrast, the report cautions: "Introduction of varieties selected for high yields has resulted in greater post-harvest losses where the new varieties are not as well adapted to the post-harvest conditions as traditional varieties. This problem should be a consideration both in selecting high-yielding varieties and in providing for their post-harvest treatment."
Rodents, grain-eating birds, insects, moulds, and physical deterioration may strike crops that stand too long in the field. In threshing and milling, grain may not be separated from the plant and impurities may be introduced. Drying of a grain crop is vital to block seed-germination and attack by insects and mites and to cut moisture in order to prevent growth of fungi and bacteria, yet over-drying can cause the seed coat to break. According to the report: "Clearly, particular methods of drying must be selected for the particular climatic, economic, and social circumstances in which they will be used. This is especially true where existing drying methods have evolved over long periods of time to meet community and family survival needs. Alternative methods should not be recommended without awareness of all possible consequences to the farmers."
Post-harvest Food Losses in Developing Countries. By the Steering Committee of Study on Post-harvest Food losses in Developing Countries, Board on Science and Technology for International Development; Commission on International Relations, National Research Council. Board on Science and Technology for International Development, 1978. 215 pp. Available from the Board; supply limited.
Damage to grain in storage is minimized by use of cool, dry area, clean containers, separation of new and old grain stores, and remoteness from fields in order to reduce proximity to concentrations of insects, the committee said. Some traditional pest-control methods, such as mixing ash with grain, are effective, and "every effort should be made to build on traditional technology and innovations should be undertaken with understanding of the social and economic implications." This is particularly important with "insecticides that present severe health hazards and have other environmental, ecological, economic, and social implications (such as over-optimistic expectations that new technologies will solve all problems and remove all need for traditional efforts)." However, the committee reported that insecticides might have to be used.
Complicating the problems of post-harvest loss, the committee said, is the possibility of some farmers and processors perceiving a prospect of higher prices and more income in times of scarcity. The committee also said that, measured in terms of human suffering and economic cost, the Post-harvest losses from food crops "represent an international challenge that richly merits priority attention."