Grain

Infobox on Grain
Example of Grain
Facts
Origin	-
Stowage factor (in m3/t)	-
Angle of repose	-
Humidity / moisture	-
Oil content	-
Ventilation	-
Risk factors	-

Grain

Description

Usually shipped in bulk, also in bags, especially seed grain. Grain is liable to damage by heating, infestation, sweat and contact with water. When grain gets wet, growth immediately starts, not only in the grain itself, but in the mould spores, yeast cells and bacteria, which are always present, causing respectively germination, fermentation and putrefaction.

Treatment for water damage is somewhat theoretical because of the necessity to apply treatment before deterioration sets in, and this is usually impossible, but when the condition of the grain is such that the cost of drying would be justified by the result, this is the only manner in which damage of this nature can be minimized.

If wetting is caused by salt water, drying out to recover the grain would not prove to be a financially viable exercise. Contamination by water causes deterioration and local heating, but general heating in grain is due to inherent vice as a result of the moisture content in the grain being too high or the period in the ship’s hold being excessive. Moisture levels for grain should be between 10% and 16%, but not exceeding 13% for maize.

Heating in dry materials may also be caused by the activity of bacteria. As a result of the feeding of bacteria, together with breathing in of oxygen, carbon dioxide and water vapour are emitted into the air. In the process, heat is produced and the temperature of the commodity rises. The higher the temperature, the more active the bacteria is in breaking down the food material into carbon dioxide and water vapour and thus more heat is produced. This may continue until the temperature reached is harmful to the bacteria and this moves outwards from the ‘hot spot’. Thus the heating and the damage become widespread in the commodity.

When heating within a bulk of a commodity takes place, due to bacteria activity, air convection currents carry water vapour upwards from the hot spot, this then condenses in the colder surface layer, raising its moisture content. This process may be carried far enough to cause the growth of moulds and bacteria and, in the case of grain, to cause sprouting. This type of water damage is essentially a surface phenomenon and is confined to the top few centimeters of a stack or bulk.

Delay in transit may of itself give rise to heating and so cause the grain to have the appearance of damage arising out of insufficient ventilation, but this condition may have arisen entirely as a result of delay. High temperatures in stowage can activate and cause infestation to develop. Grain in process of fermenting may give the appearance of having been in contact with oil, especially by reason of the odour.

Weevils impair the quality of grain, especially in the case of maize to be used for the manufacture of breakfast cereals.
Damaged grains should be disposed of as quickly as possible to avoid further deterioration. Apart from damage from an external cause, there is also the possibility of heat-damaged grain which occasionally occurs in grain stored against engine room bulkheads.

Green Corn
Subject to heating which may result in discoloration, toughening, drying out of the husk and shriveling of the corn. Attack by worm at the tip of the corn does not destroy the food value unless it is extended to the kernels themselves.

Potential for loss
There is potential for loss throughout the grain harvesting and marketing chains. During stripping of maize grain from the cob, known as shelling, losses can occur when mechanical shelling is not followed up by hand-stripping of the grains that are missed. Certain shellers can damage the grain, making insect penetration easier. For crops other than maize, threshing losses occur as a result of spillage, incomplete removal of the grain or by damage to grain during the threshing. They can also occur after threshing due to poor separation of grain from the chaff during cleaning or winnowing. Incomplete threshing usually occurs in regions with high labour costs, particularly at harvest time, when labour is too scarce and expensive to justify hand-stripping after an initial mechanical thresh. Certain mechanical threshers are designed only for dry grain.

A wet season's paddy harvest may clog the screens and grain will be lost. Cleaning is essential before milling. On the farm, cleaning is usually a combination of winnowing and removal by hand of heavier items such as stones. Losses can be low when the operation is done carefully but high with carelessness. With correct equipment, cleaning losses should be low in mills, but grain may be separated together with dirt or, alternatively, dirt may be carried forward into the milling stages. In drying, grain that is dried in yards or on roads, as is common in parts of Asia, may be partially consumed by birds and rodents. Wind, either natural or from passing vehicles in the case of road drying, can blow grain away.

The main cause of loss during drying is the cracking of grain kernels that are eaten whole, such as rice. Some grains may also be lost during the drying process. However, failure to dry crops adequately can lead to much higher levels of loss than poor-quality drying, and may result in the entire harvest becoming inedible. Adequate drying by farmers is essential if grains are to be stored on-farm and poorly dried grains for the market need to be sold quickly to enable the marketing-processing chain to carry out adequate drying before the grains become spoilt. With a high moisture content, grain is susceptible to mould, heating, discoloration and a variety of chemical changes. Ideally, most grains should be dried to acceptable levels within 2–3 days of harvest. One of the problems in assessing levels of post-harvest loss is in separating weight loss caused by the very necessary drying operations from weight loss caused by other, controllable, factors.

Milling to remove the outer coats from a grain may take place in one or more stages. For paddy rice considerable mechanical effort is needed to remove these layers. Any weakness in the kernel will be apparent at this stage. Even with grain in perfect condition, correctly set milling and polishing machinery is essential to yield high processing outturns. Complete separation of edible from less-desired products is always difficult to achieve but, even so, there are significant differences in milling efficiency. In the case of rice, milling outturns can vary from 60% or less to around 67%, depending on the efficiency of the mill. Even a 1% increase in yield of whole grain rice can thus result in huge increases in national food resources.

Grains are produced on a seasonal basis. In many places there is only one harvest a year. Thus most production of maize, wheat, rice, sorghum, millet, etc. must be held in storage for periods varying from a few days up to more than a year. Storage therefore plays a vital role in grain supply chains. For all grains, storage losses can be considerable but the greatest losses appear to be of maize, particularly in Africa. Losses in stored grain are determined by the interaction between the grain, the storage environment and a variety of organisms.

Contamination by moulds is mainly determined by the temperature of the grain and the availability of water and oxygen. Moulds can grow over a wide range of temperatures, but the rate of growth is lower with lower temperature and less water availability. The interaction between moisture and temperature is important. Maize, for example, can be stored for one year at a moisture level of 15 per cent and a temperature of 15 °C. However, the same maize stored at 30 °C will be substantially damaged by moulds within three months. Insects and mites (arthropods) can, of course, make a significant contribution towards the deterioration of grain, through the physical damage and nutrient losses caused by their activity.

They can also influence mould colonisation as carriers of mould spores and because their faecal material can be utilised as a food source by moulds. In general, grain is not infested by insects below 17 °C whereas mite infestations can occur between 3 and 30 °C and above 12 per cent moisture content. The metabolic activity of insects and mites causes an increase in both the moisture content and temperature of infested grain. Another important factor that can affect mould growth is the proportion of broken kernels. There are about 1,700 rodents in the world, but only a few species contribute significantly to post-harvest losses. Three species are found throughout the world: the house mouse (Mus musculus), the black rat (Rattus rattus) and the brown rat while a few other species are important in Africa and Asia.

An attempt should be made to approximate the magnitude of the value of losses before time is spent on trying to reduce them. If this value proves to be low, expenditure of appreciable resources on reducing losses may not be justified. However, despite efforts over the years to develop acceptable techniques for measuring grain losses, this remains an imperfect science. A particular problem with measurement is that grain does not follow a uniform sequence from producer to consumer. Harvested grain can be specially dried and treated for a family's consumption or for use as seed. Some of any harvest may be held for short-term storage, some more for long-term storage, and the rest may be sold either in one go or over a period of time, through a variety of different marketing channels. There are particular difficulties associated with accurately measuring on-farm storage losses over a long period when farmers are continually removing grain from stores to meet their own consumption needs. Further, the surplus generated by a farmer at any one harvest will dictate the quantity stored and the quantity sold, which, in turn, may influence loss levels. Given the lack of a consistent chain, care must be taken to avoid generalizing from particular measurements. "Inordinately high- and low-loss situations must be put into perspective rather than giving them overemphasis as has been the case in some instances."

The origin and justification of grain-loss estimates has thus never been particularly well- founded and attempts to measure losses suffer from the fact that it is an extremely complex exercise to do well. The costs of developing accurate measurements may simply not justify the cost and time involved in doing the work. In an attempt to get round some of these problems the African Post Harvest Losses Information System (aPHLIS), which was established in 2009, plans to develop a picture of losses over time as information becomes available, drawing on a network of local experts who contribute the latest data. It aims to provide data that are transparent in the way they are calculated; adjustable year by year according to circumstances and upgradeable as more (reliable) data become available.

There have been numerous attempts by donors, governments and technical assistance agencies over the years to reduce post-harvest losses in developing countries. Despite these efforts, losses are generally considered to remain high although, as noted, there are significant measurement difficulties. One problem is that while engineers have been successful in developing innovations in drying and storage these innovations are often not adopted by small farmers. This may be because farmers are not convinced of the benefits of using the technology. The costs may outweigh the perceived benefits and even if the benefits are significant the investment required from farmers may present them with a risk they are not prepared to take. Alternatively, the marketing chains may not reward farmers for introducing improvements. While good on-farm drying will lead to higher milling yields or reduced mycotoxin levels this means nothing to farmers unless they receive a premium for selling dry grains to traders and mills. This is often not the case.

Thus part of the problem with uptake may have been an overemphasis on technology, to the exclusion of socio-economic considerations. In the case of drying, it may be a more appropriate solution to strengthen the capacity of mills and traders to dry than attempt village-level improvements. There is thus a continual need to balance and blend technically ideal procedures and approaches with social, cultural, and political realities. Past on-farm storage interventions that have proved less than successful have included the promotion of costly driers in W. Africa that fell victim to termites when made with local wood or bamboo and were too expensive when constructed with sawn wood. In the 1980s, there was considerable enthusiasm for the introduction of ferro-cement and brick bins throughout Africa, but these were often found to be too complicated for farmers to construct, and too costly. Small Breeze block silos also experienced construction difficulties and were found to be not economically feasible. Storage cribs made of wood and chicken-wire were introduced by donors but rejected by farmers because sides made of chicken wire showed others the size of each farmer's harvest.

Reference is made to the relevant IMO publications of hazardous cargo.

Full information on this product is in the process of completion.