Potential Breakthroughs in Grain Handling
Appendix A identified technological advances that might boost the production of indigenous African grains. Here we identify other advances that might similarly influence the methods of milling and storing those grains. These, too, are innovations that, in principle, could bring outstanding benefits continent-wide. Again, however, it should be realized that they are just a smattering of examples that caught our attention as the book was being prepared. Other cutting-edge technologies may be as good, or better.
NO MORE POUNDING
Every day of the year, perhaps 50 million Africans—most of them women and children—spend hours preparing the grain that their families will eat that day. They usually soak the grain in water, pound it with the butt end of a heavy wooden pole (pestle) to knock off the outer seed coat, winnow the beaten mixture to separate the bran, moisten the grain a second time, and finally pound it yet again to break it up into flour.
This is always a hot and disagreeable task. It limits both cereal use and life itself. Decorticating enough pearl millet for a family meal (about 2.5 kg) takes two women about 1.5 hours; converting the product into flour with a mortar and pestle requires an additional 2 hours, sometimes more. Moreover, because the flour spoils quickly and cannot be put aside for later use, it has to be done day after day, in fair weather and foul, and regardless of sickness or other indisposition.
Probably no single development could help rural Africa more than relief from this never-ending drudgery. It would recover millions of "lost" hours every year, it would improve health and family welfare,
Sorghum and Women
Sorghum is a women's crop in Africa. To a large extent, they are its planters, cultivators, and harvesters. Through the accumulated wisdom of centuries, women have amassed information about the crop and its handling. Many are expert in distinguishing closely related varieties . . . a knowledge which men—even professional scientists—seldom attain. Only now, however, are researchers beginning to pay attention to this knowledge.
Joyce Kanyangwa is one of those. Working under the auspices of Texas Tech University, she traveled to three sorghum-growing areas of Lesotho, visiting selected households to gain a perspective on attitudes about the use of sorghum. ''I was interested in finding out what might be done to expand the use of sorghum in the diet to give women more income for their labor, as well as a cheaper staple for their tables," she explains.
Her research indicates that improving sorghum use can do much to help Africa's women. "Sorghum is a woman's crop, but the market for the product is limited primarily to brewing beer for men," she notes.
Better processing methods are particularly needed. The processing and cooking of sorghum and millet takes more time than rice. Women going to work, either in the fields or in the community, have less and less time available for processing and cooking. Small-scale rural sorghum and millet processing mills, like the rice mills already available in India, could help promote the consumption of sorghum and millet.
"When sorghum is processed using a special machine, people like it," Kanyangwa says. "I'm optimistic that the crop has the potential for helping female-headed households feed their families better and for helping women make more money."
The introduction of suitable dehullers and flour mills will:
and it would make the whole continent more productive. Perhaps most important in the long run, it would secure the future of the local grains. At present, the burden of the terrible toil is causing a silent rebellion against sorghum, millet, and the other indigenous cereals.
Now an option is emerging. Small power mills can, in just a few minutes, perform the task that now absorbs so much human energy and time. Some of the most successful consist of a series of 8 or 12 grinding stones of the type used for sharpening tools. The essential component, the dehuller, was originally designed at the Prairie Regional Laboratory in Saskatoon, Canada. A small version specially sized for rural Africa has been built, field-tested, and improved at The Rural Industries Innovation Centre in Kanye, Botswana. It is powered by a small diesel engine.
Reportedly, the machines waste no more grain than hand pounding does. (Recovery rates of 85 percent have been achieved, which is 10 percent better than is normal in the village.) Also the machine-dehulled grains apparently make no detectable changes in local foods. Since they use dry grain, the dehullers are more flexible than traditional methods, and the resulting flour can be stored.
The dehuller does only half of what African women do: it takes off the seed's outer layer, leaving white, ricelike grain. A further grinding is needed to make flour or grits. To do this mechanically, a hammer mill is employed. In some cases, the dehuller and hammer mill are combined into a single unit.
Although these mechanical systems were designed primarily for processing sorghum and pearl millet, they have also proved satisfactory for fonio and food legumes such as cowpeas and pigeon peas.1 One of the main attractions is their capacity to handle (without major adjustment) grains of widely different size.
Under a Canadian-sponsored program, different models are currently being developed or distributed for use in Senegal, the Gambia, and Zimbabwe. Mali and Niger, following Botswana's lead, are creating designs suitable for local toolmakers to build.
Mechanized processing probably has its most immediate use in cities and towns. In rural areas, people must carry their grain to the mill and then carry home their flour and bran. For them, the chore of carrying several kilograms several kilometers may be just as onerous as staying home and pounding the grain with a pole. However, there are ways to circumvent this. In Botswana, for instance, a donkey cart is being made available without charge to carry the grain and flour back and forth. (The donkey is fed on the customer's bran waste.) Also, the milling unit could conceivably be mounted on a cart and
wheeled to the customers. Thus, for example, a mobile mill might stop at various villages once a week and process the grain on the consumer's own doorsteps. A hammer mill perhaps might not work on such a system, but the dehuller alone would relieve the major and most unpleasant part of the drudgery.
All of this opens the possibility of substantially lessening the burdens that at present fall so heavily on millions of people. It will probably widen the mix of crops they grow. It could increase lifestyle options and employment opportunities by freeing women from the daily morning and evening chore of pounding grain. It may contribute dramatically to better health among women and children, provide time for more productive pursuits, create better markets for farmers, and lead to a more stable food situation for many countries.2
Despite the fact that people must pay to have their cereal mechanically milled, this mini-milling industry is already starting to take hold in parts of Africa. Several nations have introduced the Canadian-type mills, and support for their maintenance has quickly spread, even into remote areas. Moreover, merchants and consumers throughout Africa are showing increasing interest in buying and using flours instead of unprocessed grain. A grain revolution seems to be arising, bringing new options for farmers and consumers, as well as new possibilities for a better life in the rural areas.
To worry only about grain production is not enough: what counts is the amount and quality of the food that gets into people's bodies. Today, unfortunately, much of Africa's cereal crop never gets that far—it spoils or is lost sometime after the harvest. Estimates suggest perhaps 25 percent of each year's food production is either lost or rendered unfit.3 The reasons are clear. During handling and storage, heat and humidity foster molds and rots that ruin much grain. Insects, rodents, and birds steal enormous amounts. Most subsistence farmers store their harvest in small granaries (capacity 1.5 tons or so) and 1020 percent usually deteriorates or disappears before it can be eaten.
An obvious answer is better storage, and these days pest-proof silos built of several materials are showing much promise. Examples follow.
A Zimbabwean engineer, Campbell D. Kagoro, has for years been developing a granary built of local brick.4 His structures—known as ENDA granaries—have been installed in dry, poverty-prone areas of Zimbabwe. People there (as elsewhere in Africa) know how to manufacture baked-clay bricks. To build the silos, they lay the bricks directly on gravel-covered soil or on rock. (In some instances, wooden joists and masonry footings are used.) They cover the final structure with a waterproof thatch roof. The silos have a capacity of about 2.5 tons and may include up to five compartments for storing different products. They are equipped with air vents and are said to offer excellent protection against dampness, insects, and rodents.
A form of reinforced concrete, ferrocement utilizes materials that are normally readily available—wire mesh, sand, water, and cement. It does not corrode easily and can last a lifetime.
Experience in Thailand and Ethiopia has demonstrated that ferrocement silos can be built on site relatively inexpensively, using unskilled labor and only one supervisor. In such silos, losses are less than 1 percent per year. Rodents, birds, insects, and dampness cannot get in.5 If the bin is well constructed and its lid tightly sealed (tubing from a bicycle tire makes a useful gasket), even air cannot get in. Inside an airtight silo, the respiring grain quickly uses up the oxygen. Insects (eggs, larvae, pupae, or adults), as well as any other air-breathing organisms introduced with the grain, are then destroyed.
The possibility of putting ferrocement silos on every farm is demonstrated by a remarkable program in Thailand. There, where the concern is storing pure water rather than grain, the government has provided three ferrocement jars (each two cubic meters in size) for every family of six in rural areas. The project involved three million families and nine million jars. Each jar costs $20, but the per-capita cost—because a revolving fund of $13 million is recoverable—can be as low as 42 cents.
Heat is a basic problem with ferrocement (and most other) silos. Bins in the burning sun can warm up so much that moisture evaporates
from the grain, collects at the top, and fosters molds or sprouting. For this reason, silos should always be located in the shade of trees or houses, sunk in the ground, or surrounded with some rough-and-ready sun shield (thatch or scraps of foamed plastic comes to mind).
Although much of the promise is for small bins for household use, ferrocement can also be used to construct large storage facilities for town or regional use. One of the most intriguing is the horizontal "sleeping silo" pioneered in Argentina (where they are used mostly for storing potatoes). These large structures are shaped like the hull of an upside-down ship half buried in the ground. Bulkheads give strength and also create separate compartments in which different products or different owners' products can be stored. Compared to the towering grain elevators now used in much of the world, the horizontal counterparts lie on the ground and require little in the way of engineering, footings, or structural reinforcing.
Recently, an airtight grain store made from clay and straw has been introduced to Sierra Leone. The silo, demonstrated by Chinese instructors brought by the UN's Food and Agriculture Organization (FAO), is simple in construction, low in cost, and has potential to significantly decrease postharvest grain losses.
The raw materials in this case consist of mud and straw, and the finished silo is roofed with boards, straw, reeds, or other waterproof materials. Its inventors are the peasants of northeast China who, from time immemorial, have built tiny mud turrets to store their household food reserves. In recent years, a national campaign to decentralize grain storage has led to this very simple and economical technique being used throughout the Chinese countryside. In fact, mud silos are now being built as large as 8 m in height and diameter, to hold 200 tons.
Ghana, too, has been testing improved mud silos.6 Instead of ordinary mud, however, sun-dried molded mud bricks, from a locally made mold, are used for the circular wall. The top is a separately molded mud slab. The whole unit is sealed with a mixture of mud and clay, and the wall is whitewashed to maintain coolness.
Neither of these two silos requires any great expertise to construct or use.
Researchers in Australia and the Philippines in recent years have jointly developed sealed plastic enclosures for storing grain in ware-
houses located in the humid tropics. In 1992, a new project was begun to design a counterpart suited to the smaller-scale and outdoor needs of cooperatives, small millers, and merchants. The scientists have developed a plastic container that is rodent- and insect-proof and protects grain against the extremes of the tropical environment. It is also simple to fumigate and suitable for storing damp grain before drying. The plastic silos have been designed using the general principles already employed for storing bulk grains in Australia. Although conducted in and for the Philippines, this work seems suitable for application throughout the humid tropics.7
Israel's agricultural research organization, familiarly known as the Volcani Institute, has pioneered development of simple, cheap, and easily movable grain stores with capacities up to 1,000 tons. These collapsible, tentlike structures can be taken down, trucked to a new site, and quickly reassembled—a novel feature that makes them especially useful for handling emergency food supplies and for storing excess grain from unexpectedly bountiful crops. The walls are constructed of rolls of strong wire mesh (actually weldmesh fencing material), but the grain is held within UV-resistant plastic liners. These silos are sufficiently airtight to control insect infestation without requiring pesticides. They are primarily for use in drier areas.
Insects and rodents are not the only grain despoilers. Insufficient drying also leads to vast amounts of damage. Dampness fosters molding, sprouting, and decay that renders grain inedible. Drying the grains before storing them is therefore vital. Techniques for doing this under Third World conditions are being devised in several parts of the world.
Farmers in six districts of Sierra Leone are replacing traditional mud floors, used for drying freshly harvested rice, with improved drying yards. This cheap and simple change keeps the grain clean, lessens the drying time, and reduces postharvest losses by more than half.
The Food and Feed Grains Institute of Kansas State University has designed a new kind of dryer for developing country use. It has no fan or other moving parts and uses heat generated by burning weeds, rice husks, agricultural by-products, or other wastes.
This natural-convection, hot-air drying could open up new options in many areas of Africa where today the only cereals that can be grown are those that mature after the rains have ceased (when grains can be dried in the sun). In 1990, Kansas State tested its dryers under conditions of very high rainfall in Peru and Belize. Sun-drying was impractical, even impossible, but the new dryer proved very effective: rough rice was reduced from a level of 20 percent moisture to 14 percent in only about an hour. While this is too fast for everyday practice with rice, it clearly demonstrated that the dryer would perform well in the dampness of the tropical rainy season.
The Asian Institute of Technology (AIT), near Bangkok, has developed a simple solar dryer, constructed of bamboo poles and clear plastic sheeting.8 It can process up to one ton of rice at a time and even in the wet season can reduce the moisture content from 22 percent down to 14 percent in about 2 days. It is said to cost only around US$150 to build.
In this device, sunlight passes through a clear plastic sheet and strikes a layer of black ash (burnt rice husk) or black plastic sheet. This absorbs the solar energy, converting it into warm air. The heated air rises by natural convection through the slatted floor of the rice box, up through the grain (contained in fine wire mesh), and out a tall chimney (again fabricated from bamboo and plastic sheet).
In the early 1980s rice farmers in South Korea faced postharvest losses of about 10 percent. But now those losses have been halved, thanks to a new technology.9 The system has been so successful that just 8 years after the project was launched, 70,000 dryers had been purchased. By 1995, half a million are expected to have been built.
With this method, the grain is dried using a low-temperature process that mainly exploits the drying potential of ambient air. Basically, a fan blows air through grain in a silo. The process is cheap, requires little capital investment, and the silo can subsequently be used for storage purposes. To enable drying in humid weather and during the night, a small electric heater is used to heat the ambient air a few degrees.
In practice, the dryer is a room-sized brick structure, with a false floor to prevent soil moisture from seeping up. The air is uniformly distributed using wood or sheet metal air ducts, laid on this false floor. The air is pushed through the piled-up grain by a small 400-watt electric fan.
KILLING STORAGE INSECTS
The need to protect Africa's stored food from insects is particularly important these days. The larger grain borer, a Central American beetle introduced accidentally into Tanzania and West Africa, is relentlessly spreading through maize-growing areas. This voracious pest feeds on stored maize, cassava, wheat, sorghum, sweet potato, peanuts, and other foods. The destruction it causes can be devastating; in tests in Tanzania up to 34 percent of cob maize in a crib has been destroyed after only 3 months, and up to 70 percent of dried cassava after only 4 months.
Insects get into even the best silos when the grain is added. Previously, there were no cheap and effective controls for subsistence farmers to use. However, some innovations follow that might help overcome the problem.
Researchers in India have found that farm produce can be disinfested by "roasting" the bugs in the sun. They first wrap a square sheet of black polyethylene around two slats of wood, leaving a "mouth" at either end. After filling the resulting pouch with produce to a depth of 3 or 4 cm, they seal the ends by weighing them down with slats of wood or bags of earth. Finally, they add a covering of transparent polyethylene. This transmits sunlight through to the black inner pouch and traps the heat inside.
The inventors, T.S. Krishnamurthy and colleagues,10 report that insects, at all stages of the life cycle, die when kept at 60°C for 10
minutes. They tested pouches of varying sizes containing several kinds of produce, including wheat, rice, pulses, and semolina. A pouch containing 40 kg of peanuts, for example, reached an internal temperature of 67°C in just 4 hours. Wheat took 6 hours to reach 61°C. No insects survived.
Neem (see Appendix A, page 279) is an Indian tree that has been introduced widely in Africa and now can be found from Mauritania to Mauritius. People in neem's homeland have long known that ingredients in its leaves and seeds can disrupt the lives of storage insects. For thousands of years, Indians, for example, have placed neem leaves in their grain bins to keep away troublesome bugs. Now, scientists are finding that there is technical justification for this process and commercial neem-based pesticides are already being employed in the United States.11
With all the neems in Africa (not to mention the new ones being planted because of the rising international enthusiasm for this tree), neem-based methods for controlling insects in grain stores are soon likely to be widely available.
Some German-sponsored research has already pioneered one approach that employs the oil extracted from neem seeds.12 In this project, neem oil has proved effective against bruchid beetles—the prime pest of Africa's stored products. Amounts as small as 2-3 ml per kg of stored food will protect grains and legume seeds up to 6 months-long enough to overcome the critical period when bruchids and other storage insect pests are active.
In Togo, a program for teaching farmers how to protect seeds with neem has been under way for the past 15 years.13 Now Niger, Senegal, and other nations are following suit. Neem oil imparts no bitterness to the food. In trials, people could not distinguish the seeds protected by it.
Probably in the long run, however, it will be neem leaves that are used most. This is the simple technique employed since ancient times in India. The leaves are merely added to the grain at various levels in the bin. The leaves eventually dry out, turn to powder, and (for all intents and purposes) disappear. The important thing is that bruchids, weevils, and flour beetles disappear also.
See the companion report Neem: A Tree for Solving Global Problems for more information. For a list of BOSTID publications, see page 377.
See also Appendix A. page 279.
Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ).
For some time researchers have known that certain powdery minerals can kill insects. The sharp-edged dust particles "spear" through the thin joints between the horny plates of the animal's exoskeleton. This was first recognized with diatomaceous earth, a widely available, completely safe powder that kills cockroaches almost on contact. Now scientists in Nigeria have found that a common local mineral called "trona" also works in the same way—at least on certain storage pests.
In experiments, powdered trona proved lethal to the maize weevil (Sitophilus zeamais), causing almost 100 percent mortality after 15 days of exposure. It also reduced the maize weevil's fecundity in grains treated with the dust.14
Trona, Na2CO3·NaHCO3·2H2O, is a crystalline carbonate/bicarbonate that occurs naturally in several parts of Africa. It is apparently not toxic to humans and livestock. Indeed, in most African countries, rural people use it as a food additive.15 For example, they commonly drop it into okra soups to increase the mucilaginous quality or into boiling cowpeas to reduce the cooking time. In northern Nigeria, farmers add trona to their cattle's drinking water.
Mixing trona dust with maize grains (at 1.5 percent by weight or more) killed or inhibited the biological activities of the most ubiquitous pest of stored maize, the maize weevil; but another noxious pest, the red flour beetle (Tribolium castaneum), was unaffected.16
Mineral dusts may never be fully reliable in grain-store insect control, but their permanence, low toxicity, and ready availability make them attractive possibilities for a simple, cheap, and ubiquitous answer to at least part of the massive and widespread storage losses.