Organisation: Pakistan Agricultural Research Council (PARC)
Although post-production operations vary from country to country and region to region throughout the world, procedures are similar among the developing countries. However, operations diversify with farm size such as small landholders, medium scale farmers and progressive growers. Post-production operations will be dissimilar between the developed and developing countries. Functions like harvesting, transportation, threshing, cleaning, drying, storage, packaging and marketing are described below.
A major proportion of the crop in Asia is harvested manually using sickles (over 70 percentage in Pakistan, India and Bangladesh - Figure 2) or with types of knives leaving 3-6 cm wheat straw above the ground level. Methods and timing of harvesting are important factors to total crop yield. In South Asia wheat is harvested in the dry summer months from March to May. Farmers are conscious of the fact that the harvested wheat should be dry enough for threshing and storage. Artificial drying is uncommon. The manually harvested wheat crop is tied into small bundles and stacked in bunches of 10 - 15 bundles, which are left in the field for one to three days to dry (Figure 3). Combine or mechanical harvesters (Figure 4) yield a higher proportion of immature grains and pose a moisture hazard, leaving no time for the grain to dry.Figure 2: Woman harvesting wheat manually Figure 3: Manually harvested crop left to dry on the field Figure 4: Mechanical harvester
Labour-intensive systems of grain movement serve to minimise capital investment in countries where the cost of labour is low. Most wheat is manually loaded and unloaded from wagons, trucks, railroad cars, and barges between farm and mill. The greater the grain loss the higher the cost. In some situations, bagged wheat may be loaded on and off vehicles ten times manually before it is milled.
Highly efficient bulk handling systems exist in developed countries to load loose wheat into trucks. Using an auger, wheat is moved to the grain-processing centre in a single trip, dumped into a receiving bin, carried by a mechanical conveyor through the cleaning and drying processes and into storage. Next, it is moved out of storage into the flour mill at the same location, where the finished flour is mechanically bagged, loaded into trucks by elevator, and taken to a commercial bakery or retail market without once being handled manually. National policy regarding the appropriate degree of mechanical wheat handling is often based on the need to maximise employment for unskilled labour.
In South Asia post-harvest handling, transport and storage of grains at the farm level is done partially in bulk. The transportation of grain to primary markets by the farmers is also done in bulk using bullock carts, tractor trolleys or lorries. At the market yard, the grain is displayed in bulk, auctioned, cleaned, bagged, weighed and delivered to consumers in bags. The food grain trade depends upon labour. Therefore, handling, transport and storage of marketed grains in bags is common. Availability of cheaper jute bags in these countries also encourages handling, storage and marketing of grain in bags. Large quantities of food grain have to be moved through rail or road transport, another major factor promoting use of bags.
From farms in Pakistan, wheat is mainly transported in animal driven carts or carried on camelback. Large farmers use tractor driven trolleys and trucks. In each case bags are used for transportation. Problems arise when old torn bags are used which spill grain, causing loss. Mostly 100-kg bags are used which are cumbersome to carry. Other hazards for bags are hooks which tear the bags, the rough surface of the carts and trolleys and nails, which damage sacks when they are pulled. Transportation occurs from farm to market, market to consumer, market to temporary storage, temporary storage to long term storage and long term storage to consumers.
The sheaves of wheat are carried to the threshing floor manually or on the backs of animals like camel donkeys and bullock (Figure 5). Tractor trolleys and bullock carts are mostly used for transporting harvested wheat crop to the threshing floor where they are spread out to dry in the sun and wind for a few days. The threshing and separation of the grain from the straw is done in a variety of ways. The wheat crop may be beaten with sticks or trampled by a bunch of animals. Animals may be used to draw a wheat bundle/stone roller over the thick layer of harvested wheat crop. Or, an implement consisting of a series of steel disks may be used. In some locales, a tractor may be repeatedly driven over the wheat stack spread on the threshing floor.Figure 5: Animal transport to threshing floor
The tractor-drawn thresher (Figure 6) and self-propelled harvester combine causes the least grain contamination, but are capital intensive solutions. Farmers, who cultivate only one or two hectares a season, hire small threshers, which are, light enough to be carried from one field to another by two people. Pedal or motor-driven mechanical threshers have been devised. One type has a revolving drum with projecting teeth that strip off the grain when a sheaf of wheat is held against the moving surface.Figure 6: Tractor-drawn thresher
After threshing, the straw (bhoosa) is stacked around the threshing floor (Figure 7), and used as animal feed, bedding, cooking fuel, to make sun-dried bricks, or compost. The wheat grain will be contaminated with pieces of straw chaff, broken grains, stones, and dirt when it is spread on the threshing floor for further drying.Figure 7: Straw stacks around the threshing floor
Labour saving schemes are employed in some farming communities. An old and simple improvement in threshing is to beat a sheaf of wheat and the grain heads against a low wall, an oil drum, or a wagon bed. This method is more efficient than trampling as the grains fall into a container or onto a woven mat. Small quantities are threshed but are less likely to become contaminated.
In many developing countries manpower is shifting from cereal production to cash crops or to industry causing a dearth of manpower in the urban areas. However, by tradition, the whole family participates in the harvesting and threshing process together with borrowed or hired labour. Women also join in these activities. In places where mechanical harvesters are used women do not participate. Labour prefers to be paid in kind than in cash. In typical communities, the farmers share resources of the village. Manpower reciprocates labour in the harvesting and threshing schedule. Whenever threshing is by bullocks, the community shares the threshing floor and animals.
Threshing is mainly mechanical (60-80 percentage) in Pakistan. Tractor-driven threshers and at times combine harvesters are used. The design and maintenance of the thresher are central to reducing the broken grain percentage. Threshing using animals is also common in many areas of Pakistan. Several animals continuously walk around a pole to crush the wheat straw and heads to separate the grains and convert the straw to bhoosa.
The most critical decision in harvesting is not the degree of mechanisation but the timing of the harvest. If the harvest starts late, the grain becomes too dry and rate of grain shattering is high. The longer a ripe crop is left in the field or on the threshing floor, the higher will be the loss from natural calamities including hailstorm, fire, birds, or rodents. The moisture content of the grain will be high, making drying difficult if the harvest start too early.
The moisture content of wheat grain is a crucial factor from harvest until milling. Moisture content of 25 percentage is not uncommon in newly harvested grain in humid areas but it must be dried immediately to protect it against mould. At 14 percentage moisture grain can be safely stored for 2 to 3 months. For longer periods of storage from 4-12 months, the moisture content must be reduced to 13 percentage or below.
Drying in many wheat-growing countries of Asia, Africa, and Latin America is done by spreading a thin layer of grain in the sun, on the threshing floor or on rooftops. Mechanical drying of wheat grain is not practised in most of the developing countries. It is mostly sun dried. Sun drying is risky because it depends on weather conditions leading to dirty grain, spillage loss and bird attack.
Each small farmer cannot afford mechanical equipment for cleaning and drying, but as a co-operative they could own such equipment. Some commercial grain buyers or government warehouses offer to accumulate the grain of small farmers, bulk, clean, and dry it with modern equipment. Unfortunately these services are rare in developing countries.
As the weather is quite warm at harvest, the moisture content of the grain (Pakistan) is below 10 percentage. During the rainy season moisture content slowly increases to 15 percentage. Deterioration of grain is closely related to the moisture content which is key to safe storage. Temperature and relative humidity influence moisture content of a stored product. The moisture content of wheat in Pakistan when first stored is usually low. In areas where there is heavy rainfall during summer, the relative humidity and grain moisture content increases.
The wheat delivered from the farm at harvest to the village market or to a government food corporation presents different challenges. Since mills need to be able to hold sufficient grain for 30 to 60 days of milling this wheat may be kept in sheds, large steel bins, concrete silos, or in the holding bins of a flour mill. Wheat may be temporarily stored in railroad cars or in open piles in market towns where protection is little better than on a village-threshing floor.
After threshing, the straw, chaff, immature grains, sand, stones, and other substances are separated from the grain by sieving, winnowing or hand picking. In traditional manual winnowing, a shallow basket containing grain is held overhead, and the grain is tossed during periods of fast winds. Lighter weight broken grain, straw, and weed seed are carried by the wind to one side, as the whole grain falls to the bottom of the winnowing device. The winnowing device may stand on a stool to give the falling grain longer exposure to the wind. Manual winnowing requires a continuous brisk wind and several repetitions. Even then, the results are erratic producing grain, which is far from satisfactory. Wheat cleaning is most often done manually by women, occasionally by professionals.
Simple, low-cost appliances that use hand-driven or motorised blowers have been developed that are more efficient and less time consuming than hand winnowing. A FAO publication on processing and storage of food grains by rural families describes grain mills, flourmills and sophisticated grain cleaners. Lending agencies that finance grain storage facilities can provide advice on appropriate cleaning equipment.
In South Asia and most of the developing countries, farmers for their own use for food, cattle feed and seed retain about 50-80 percentage of the grain produced. The farmers generally store their grain in simple granaries constructed from locally available materials like paddy straw, split bamboo, reeds, mud and bricks. A majority of wheat is stored in bags in a room, bin, drum or container for family consumption or is piled in farm buildings lacking proper flooring, closed doors and windows. Wheat is lost to moulds, birds, rodents, and insects. Storage varies in size and type including indoor, outdoor, above-ground, under-ground or airtight structures. Some conventional storage structures used by the farmers in Asia are:
1.Mud structures mostly bins or pots
2.Wood or Bamboo structures
3.Metallic drums, bins or containers
4.Kothis (small rooms)
5.Bokharies (straw structures)
It has been estimated that in Pakistan about 70 percentage of wheat is stored at farms in bags. The balance is stocked in the market and public sector storage partially in bulk. Wheat storage is primarily assigned to the public sector for food security.
Provincial Food Departments, Federal Food Directorate, Defence Department, National Logistic Cell and Pakistan Agricultural Supply Corporation are main public agencies, which are responsible for food security, using storage structures including house type sheds, binnishells, and silos. Some wheat is also stored in the open and covered with tarpaulin or polyethylene.