Losses in the Grain Production and Processing Chain

The main stages within the agricultural supply chain during which losses occur depend on the nature of the commodity under study and of the prevailing practices in the country or region of interest. In the case of grains (cereals and pulses), the following broad operations, and the associated causes of losses, may be distinguished.

Harvesting

The manual harvesting process includes cutting the crop, gathering, bundling and stacking. The same operations may be done mechanically by a harvester. At this stage, losses occur mainly due to the shedding of grains, with the amount of loss depending on the time of harvesting: if the harvesting operation is done late, then shedding is generally higher. When harvesting is done mechanically, a higher proportion of the grain may be damaged, resulting in additional losses.

Threshing or Shelling

Grains are separated from the husk and plant to which they are attached. The process may be performed manually or mechanically using threshers, shellers or combine harvesters. When done mechanically, additional losses may occur due to grain damage during processing. However, this does not necessarily imply that losses are always lower when threshing or shelling is done manually, as mechanical threshers may reduce losses due to spillage.

Cleaning or Winnowing

The process consists of cleaning the grain by blowing the chaff away from it. In doing so, losses occur because a certain amount of the edible grain passes into chaff. The cleaning operation may be done manually or mechanically (the winnower may be hand- or machine-operated). Contrary to the case of manual processes, the use of combine harvesters allow harvesting, threshing and winnowing to be performed in one single operation: in this situation, losses cannot be attributed to each activity.

Drying

Drying is often necessary to bring the moisture content of the grain to the recommended level for storage, selling or consumption. The causes of losses at the drying stage are similar to those arising during storage: damages and losses caused by pest infestation, rodents, birds, etc., especially if the grain is dried in the open air (yard, road, etc.), a common practice in developing countries for crops such as paddy, pearl millet or sorghum. Insufficient drying may also lead to fungal damage to grain during storage.

Storage

Grain can be stored by different actors, from the farmer to the wholesaler, using a variety of facilities and equipment, ranging from traditional granaries to metallic silos and sophisticated storage facilities with controlled temperature and humidity levels. The deterioration of stored produce, leading to weight or quality reduction, is principally caused by pest infestation, rodents, birds, etc., as well as by attacks by microorganisms (fungi, bacteria, and yeasts) and metabolic activity. Storage losses generally increase with storage time.

Processing

Food grains are subjected to different types of processing before reaching the market and being finally consumed. For instance, paddy rice is generally de-husked or dehulled to obtain brown rice, manually by hand pounding or, more commonly, by machines such as rice hullers. When processing paddy, additional operations such as pre-cleaning, de-stoning, parboiling (pre-milling treatment), polishing and glazing may also be required. During these operations, losses are essentially due to damage to the grain, certain grain kernels resulting broken, and to spillage. A key efficiency parameter for rice milling is the recovery in terms of whole grain and the percentage of broken grains resulting from the milling process. For example, according to the International Rice Research Institute (IRRI), a good rice mill will produce 50 to 60 percent of head rice (whole kernels), 5 to 10 percent of large broken kernels and 10 to 15 percent of small broken kernels . Losses can be defined in relation to these efficiency standards.

Packaging, handling and distribution

Improper packaging of produce may facilitate pest infestation or the appearance of moulds and fungi leading to grain damage, weight loss, or rejection because of spoilage, especially if the produce is stored or transported for long periods. Improper handling may lead to grain damage and spillage, resulting in weight as well as quality losses. These losses may arise at different phases, for example during transport from farm to storage and from storage to market, at different points of marketing channels, and at the wholesale and retail levels.

Transport

During post-harvest operations, transport is involved on several occasions: harvested crop may need to be moved from the field to the threshing floor, and from there to the farm storage area, and finally from the storage area to the processing facilities and collecting markets. From those markets, crops may be transported by retailers to their shops or transported by wholesalers over long distances to distant or foreign markets by train, trucks, ships, etc. During these operations, which require multiple loading and unloading, spillage or pilferage entrain losses. In addition, transit losses may also occur because of damage to grain in trains, trucks, or ships caused by time-bound deterioration. In long-distance transport, grain may also be attacked by insects, fungi and other pests, similarly to what usually happens during normal storage.

Click here to view a video that explains postharvest loss bulk transportation.