Difference between revisions of "Grain"
m (→Storage / Transport)
m (→Risk Factors)
|Line 95:||Line 95:|
Latest revision as of 16:04, 12 January 2021
|Infobox on Grain|
|Example of Grain|
|Origin||Various regions in the world|
|Stowage factor (in m3/t)||Ranging between approx. 1,3 and 1,8 cbm/t|
|Angle of repose||Average approx. 25°|
|Humidity / moisture||Around 13%-14%|
|Risk factors||See text|
GRAIN (Barley, Maize, Oats, Rye, Sorghum, Wheat)
Cereals are grasses (members of the monocot family Poaceae, also known as Gramineae) cultivated for the edible components of their grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grains are grown in greater quantities and provide more food energy worldwide than any other type of crop; they are therefore staple crops.
In their natural form (as in whole grain), they are a rich source of vitamins, minerals, carbohydrates, fats, oils, and protein. However, when refined by the removal of the bran and germ, the remaining endosperm is mostly carbohydrate and lacks the majority of the other nutrients. In some developing nations, grain in the form of rice, wheat, millet, or maize constitutes a majority of daily sustenance. In developed nations, cereal consumption is moderate and varied but still substantial.
Grain is the seeds of some special kinds of grass. These grains are also called cereals. People grow different kinds of grain as food. The different kinds of grain are perhaps one of the most important foods in the world. Some kinds of grain are Barley, Maize or American Corn, Oats, Rice, Rye, Wheat.
87% of all grain grown by farmers around the world is maize. Grains contain carbohydrates that people can eat. In poorer countries, grains are a large part of the food supply. In richer countries, they are still important as food, but not as important as in poorer countries. Growing grain uses a lot of water. About 1,000 tons of water is needed to grow one ton of grain.
Many different foods are made from different types of grain. Grain is often ground into a powder called flour. Flour can be made into breads, cakes, or noodles.
Different kinds of beer are made from barley malt, wheat, and other grains.
Storage / Transport
Grain is usually shipped in bulk, but 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.
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.
The properties of grain
Grain has a comparatively low moisture content and a protective outer skin which is relatively impermeable to water. Normally in the grain trade, from harvesting to the discharge of cargo, there is a tendency for grain to lose moisture to the surrounding atmosphere. Air currents can carry moisture more rapidly through a less compact cargo such as pellets than through a powdered cargo. It is possible to transport unventilated grain without damage in tankers and to store it safely for long periods in unventilated silos. Grain possesses low thermal conductivity – heat moves slowly through grain.
Moisture in grain
All biological materials normally contain a certain amount of water. When a material is put in contact with dry air it will tend to lose a certain amount of its water to the air in the form of water vapour. This process will continue until equilibrium is reached between the material with that particular moisture content and the surrounding air at that particular temperature. In cargoes such as bulk grain, when air movement within the cargo is very restricted, the moisture content of the air within the cargo is, under normal conditions, completely controlled by the moisture content and temperature of the cargo.
If the initial moisture content of the grain is lower the difference will be less and a much greater quantity of water can be absorbed by the cooler grain before water content is raised to a level at which spoilage will begin to occur.
To quote a typical example: in a cargo of bulk maize with a moisture content of 14% and a temperature of 25°C the vapour pressure of the atmosphere within the cargo, which occupies 40% of the volume of the cargo, will quickly reach equilibrium with the maize. A relative humidity of 68% will be reached and the water vapour pressure in the air at that time will be 16,3 mm Hg. A change in the temperature of the maize will result in a change in the equilibrium relative humidity and the vapour pressure.
When a temperature difference exists within a grain cargo moisture moves slowly through the cargo in a process known as moisture migration. Regardless of what causes the temperature difference, when the moisture content is uniform, moisture always moves from areas of higher temperature to areas of lower temperature. Moisture migration is an important factor in cargo care because too much moisture in a particular area can damage the cargo. It is important to avoid any actions which will encourage moisture migration within the cargo. Moisture migration will be greater when temperatures are higher and when the sites of the different temperatures are closer together. The lower the thermal conductivity of the cargo the slower heat will move through the cargo and the less the opportunity for moisture migration. Under normal conditions the rate of moisture migration in grain is low.
For grain loaded warm and subjected to boundary cooling the major amount of moisture migration will be upwards because of the tendency for hot air to rise. More moisture will pass to the top of the cargo than to the sides. In cases where damage from sweat occurs more damage can be expected at the top of the cargo than at the sides.
A bulk cargo of grain, if stowed in accordance with Solas regulations, cannot be significantly affected by surface ventilation or by lack of it. An objective of the grain regulations is to eliminate or minimize space over the grain: this makes surface ventilation difficult or impossible.
Surface ventilation of grain cannot affect heating which is occurring more than one meter below the surface, because the transfer of heat is so slow.
Surface ventilation can do nothing to reduce or eliminate moisture migration in bulk grain. Continual surface ventilation will maintain the temperature differential and encourage moisture migration to the surface. Because of the many factors involved it would be unwise to attempt to formulate any general rules for the ventilation of cargo to minimize the effect of moisture migration. However, in most instances moisture migration within a healthy cargo is slow and is therefore not a problem.
If ship’s sweat would occur without ventilation then cargo sweat is likely if ventilation is used! Without ventilation ship’s sweat will occur only if the ship’s steelwork becomes cold enough to cool the air over the cargo to the dew point. With ventilation the surface of the cargo is cooled and warm air rising through the cargo may condense just below the surface layers causing caking and/or encouraging microbiological activity.
Grains, Oilseeds & Pulses
Whatever the methods of carriage and the problems inherent in the trade, the movement of grains comprises a considerable and versatile part of seaborne commerce. The variety of grains can be increased considerably when including their by-products.
Flour for example, is a major commodity, being the finely ground product of grain, usually of wheat. Another important cargo, bran, is formed from the husks of grains separated from flour during the milling process. Meals are the result of grains being ground less finely than when producing flour, whilst the term feed grain applies to low quality but still valuable grain or grain by-products used in the feeding of animals and poultry eg: Feed-wheat or corn gluten feed-pellets, grain unfit for human consumption may be termed de-natured.
Oilseeds from a variety of plants, are normally crushed mechanically or treated by a solvent process to remove valuable oils, and include: sunflowerseed; rapeseed; mustardseed; linseed; and lupineseed.
Seeds in bulk form are a dangerous cargo, being particularly prone to shifting at sea. It is also possible to 'drown' in a hold of such a commodity. For these reasons, adequate securing of seed cargoes in non self-trimming vessels is vital, whilst seaman and shore labour must exercise extreme caution when engaged in associated cargo work.
The residue husks (or hulls) remaining after the oils have been extracted are termed expellers, which since these remain rich in nutrient, are valued for such as cattlefodder or fertiliser.
Expellers may be shipped as they are, but are often pressed into cakes, termed oilcake or seedcake, and shipped in bulk or in bags. These cakes vary considerably in their precise carriage requirements, depending on type, origin, and oil-extraction process, but all are extensively covered in the IMO Dangerous Goods Code and/or International Maritime Solid Bulk Cargoes Code (inflammable solids). All require aging before shipment, are liable to lose wieght on passage as oil content dries out, to overheat, perhaps to spontaneously combust, to become infested by insects, to taint from other goods, and to emit strong odour.
Pellets are manufactured from grains or seeds themselves, or from residues produced in the milling process. Like oilcakes, after production they should be left for some time to cool prior to shipment. If pellets are loaded at a high temperature or with an excessive moisture content, or are adversely influenced by climatic changes during the voyage, the cargo can overheat and/or sweat. In certain circumstances moreover, pellets can emit carbon dioxide gas, with resulting danger to anyone entering cargo spaces.
Certainly ships engaged to carry expellers, oilseed cake or pellets, should be fitted with a fire smothering system, eg: a CO2 system, so as to control possible outbreaks of spontaneous combustion.
Principal grains, seeds and pulses, together with certain by-products involved in seaborne trade are amongst others:
Alfalfa: A deep-rooted plant of the pea family valued as fodder, particularly in the Americas.
Barley: A generally light stowing grain exported extensively in bulk and in bags from Canada, the EC and Australasia, and used in malt-making, bread and cattlefood, as well as for brewing and distilling. Imported in large quantities into Red Sea and Arabian Gulf countries, usually in bags.
Corn: Also known as Indian corn and widely-grown in Southern Africa, the Far East, South America and the USA. Apart from its value as foodstuff, corn has various industrial applications eg: for starch, and is rich in glucose. Corn-gluten feed pellets being a by-product are used as an animal feed which is highly regarded for its gluten protein. Corn is particularly liable to heat and to sweat, especially as a result of poor handling prior to shipment.
Durrah: A kind of millet much cultivated in Asia and in Africa as a substitute for rice, being moved in bags over relatively short sea distances.
HSS: A shipping term covering (H) Heavy Grains, (S) Soybeans and (S) Sorghums, and used in chartering/grain trading, the approximate stowage factor in bulk being 50 cubic feet per tonne.
Linseed: The versatile and widespread seed of the Flax plant, its oil being used in the manufacture of linoleum; for putty; as a preser4vative for wood; for liniments; and in mixing pigments.
Lupin: An increasingly popular, heavy stowing seed crop with a high protein content, useful as animal feed and capable of commercial growing throughout the arable world, a principal exporter being Australia.
Malt: Barley (or other grain) steeped in water until it germinates when it is dried in a kiln and used in the brewing or distilling processes, being shipped generally in small bagged quantities.
Mustard: Most of the World's commercial mustard is grown in Canada, its seed used in the preparation of a wide range of food products, including salad cream and sauces as well as mustards themselves.
Oats: A light stowing grain, particularly hardy and thus widespread, exported largely from Australia and the northern parts of Europe and America.
Pollards: A mixture of bran and meal liable to heat and to sweat, thus requiring good ventilation and dry stowage. Commonly pelletised.
- Self-heating / Spontaneous combustion
- Mechanical influences
- Toxicity / Hazards to health
- Shrinkage / Shortage
- Insect infestation / Disease
The carriage of grain in bulk is subject to the regulations of the Shipping Law.
Regulations dealing with the carriage of grain in bulk can be found in the relevant IMO publications of hazardous cargo.