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The perishable staple food crops are second only to the grain crops as providers of human food. Grown mainly in the developing countries of the humid and sub-humid tropics, where they are often much more productive than grains, they provide the main staple of carbohydrate foods for some 500 - 700 million people. The root crops, especially cassava and yam, together with cooking bananas (plantains) are the most important.
Owing to the ecological conditions prevailing in the regions, production is often continuous or semi-continuous, in contrast to grain crop staples, whose harvesting is highly seasonal normally taking place during only a few weeks, so that long term storage for nearly a year for part of the crop is necessary. With the perishable staples many societies traditionally practice a greater or lesser degree of "storage avoidance", i.e. harvesting only for immediate or short term requirements throughout much of, or even the whole year. Thus, storage systems are usually relatively short term (the yams, the most highly seasonal of the perishable crops, provide a marked exception). Processing is often undertaken as much for the necessary removal of toxic principles (cyanide from cassava, alkaloids from certain yams or the irritant principles from some aroids) as for the manufacture of processed products of long storage life, although the need for more durable products for long distance travel or as famine reserves is often recognized. Although this is the traditional pattern, changes associated with increasing urbanization and the growth of market economies are reducing the validity of the "storage avoidance" approach.
Nevertheless, many traditional societies which have been primarily dependent on the perishable staples for centuries or often millennia, have devised many highly ingenious storage and processing techniques for these staples. The culture-historical evolution of these societies in relationship to their food plants has, in general, made them strongly ecocentric in their thinking, in contrast to the technocentric philosophies prevailing in the developed world, while further their material resource bases are strictly limited. Their storage and processing systems are generally, therefore, extremely simple and have only minimal impact on the total environment. Owing to their simplicity and the fact that they are usually individually small-scale, they have often been disregarded or even despised as "primitive" by qualified agricultural scientists; this attitude has been reinforced by the fact that the vegetatively-propagated crops from which those staples are derived are poorly understood within and alien to the "Western" cultures within which scientific thinking developed.
The valuable store of traditional knowledge of the postharvest biology and technology of these crop products existing within these societies is, however, well capable of interacting with and hopefully being improved by modern agricultural science. Certainly, it should not be neglected and this report forms a first attempt to review and classify such of the available information in the subject area that has already appeared in the scientific literature. Much more doubtless exists that has never been written up. It is suggested that, especially within the concepts of "appropriate technology" or "rural technology", traditional thinking and practice could very well be applied more extensively in the development of post-harvest technologies than has been the case hitherto.
The different staples are best adapted to particular, different ecosystems, although many are nevertheless extremely ubiquitous within the humid tropics. Similarly, the crop products need different approaches in their post-harvest technologies.
The most important non-grain staple of all, cassava, has very highly perishable roots, which normally have a storage life of only days; at the same time all known cultivars contain precursors of hydrogen cyanide though at widely differing levels. Although some societies have devised techniques for storing the roots for substantial periods (which techniques have been substantially improved by recent research on curing of the fresh roots) most cassavausing cultures process the roots by any of a variety of soaking, drying or fermentation techniques to produce stable dried products in which the level of the toxic cyanide is substantially reduced.
Yams, in contrast, are fairly highly seasonal in production, although harvesting may be spread over 4 - 6 months with different species and cultivars. The edible tubers being natural organs of dormancy, they are inherently well adapted for storage when destined for use as food and indeep most of the world's yam crop is stored in the fresh state, and simple but ingenious structures have teen devised by most yam-growing societies. Nevertheless, as with virtually all the perishable staples, techniques for the preparation of dried chips and flour exist in most yam-growing societies. Grating and soaking techniques are used to detoxify certain minor species which contain alkaloids.
Both sweet potatoes and the aroid root crops are examples of perishable staple crops where "storage avoidance" is extremely widely practiced although the root tubers of the former, especially, can under optimal conditions be stored for several months. Sweet potato is mainly grown in the cooler tropics, e.g. at altitudes over 1 000 m and protection from cold is a first essential in storage: under more typical lowland tropical conditions, losses in storage are extremely high mainly owing to pathogenic factors. Similarly, the aroids which are often harvested on a year-round basis, regardless of the state of dormancy of the corms, usually have very short storage life, but it is likely that if the corms are harvested when fully dormant, longer storage life could be obtained. Processing, essentially the production of sun-dried chips or flour, is occasionally resorted to with both these crops.
Plantains and other cooking bananas have an inherently short storage life in the fresh state, though from a practical point-of-view this is somewhat mitigated by the fact that they can be utilized as food in different ways, when unripe; partially ripe; ripe or even moderately over-ripe. As ripening of the individual fruit proceeds sequentially from the proximal to the distal end of the stem, the fruit of a single stem, once cut from the plant, can often be used over a period of a month or more. For longer term storage, especially as a famine resource, sun-dried chips and flour are sometimes prepared. In certain parts of the tropical world the preparation of beer (of high solids content, and therefore nutritious) or other fermented foods is practiced, the latter having a long storage life.
Breadfruit has probably the shortest inherent storage life of any of the perishable staples, being fit for consumption only in the few days between maturity and the onset of ripening. Commonly, it is harvested only as required, or its storage life extended a few days by keeping under water. Drying into chips or flour is sometimes practiced and anaerobic fermentation techniques have been developed in the South Pacific which produce a paste which may be kept for months or even years.
Pandanus fruit are also highly perishable. They are often eaten fresh, but are also preserved as sun-dried pastes or flours, the fruit being first boiled or roasted. It is said that the flour, especially, may be kept for several years.
The stem starches laid down by monocarpic plants such as sago and other palms, and also by Ensete, are invariably processed almost immediately; the felled stems are not stored any longer than is necessary. Processing usually depends on physical removal of the stem starch, followed by wet extraction, settling and drying, usually in the sun. Fermentation techniques are used for Ensete and occasionally for sago starches.
Very little information is available in most cases concerning the division of labour between the sexes in the postharvest technology of those staples. Processing is generally little more than an extension of domestic preparation for food and is thus, most commonly seen primarily as women's work. This is especially true of cassava products.
With storage of fresh material there seems little systematic sexual differentiation of labour, both men and women being involved, either separately or together in various societies. An important exception is with yams. Virtually all operations concerning the major (though not necessarily the minor) species of yam are conducted largely, or in some societies exclusively by men, including storage and processing, only actual culinary preparation being undertaken by women.