Corn
| Infobox on Corn | |
|---|---|
| Example of Corn |  |
| Facts | |
| Origin | This table shows only a selection of the most important countries of origin and should not be thought of as exhaustive.
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| Stowage factor (in m3/t) | 1.36 - 1.39 m3/t |
| Angle of repose |
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| Humidity / moisture |
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| Oil content | - |
| Ventilation | Recommended ventilation conditions: surface ventilation ; also see text. |
| Risk factors | Due to its oil content, corn, especially freshly harvested corn, has a strong tendency to become rancid and undergo self-heating. |
Corn
Description
Corn (Zea mays) is a type of cereal belonging to the grass family (Gramineae), the term "cereals" covering the grain fruits of cultivated grasses (spikes or ears in the case of wheat, rye, barley and corn; panicles in the case of oats and rice.
Corn is a monoecious grass species, the female inflorescences (ears of corn) of which are sheathed with long bracts (shucks) and located in the axils of the central stem leaves, while the male inflorescences form large terminal tassels. An ear of corn contains on average 500 - 1000 kernels. The structure and chemical composition of the grain vary little between the different types of cereal. The cereal grain is a single-seeded indehiscent fruit, the husk of which is formed by the fusion of the fruit and seed walls. It consists of three components:
- its cracked husk, which gives the grain a greatly increased surface area relative to its mass. This allows the cereal grain to enter into an active exchange of materials with its environment.
- the endosperm, which constitutes the main component of the grain.
- the embryo.
After harvesting, corn usually undergoes further post-ripening, which consists of the high molecular weight substances congregating further with water being expelled (syneresis). As the surface of the cereal then becomes damp because of the elevated water content, this is described as "sweating. In this state, the cereal is highly susceptible to mold and must not as yet be shipped. However, if the water content of the cereal is relatively low (approx. 13 - 14%), proper storage allows the sweat moisture to be absorbed by the air without the risk of mold growth. This sweating process proceeds for a period of approximately 1 - 2 months.
The following varieties are distinguished (also by shape and size of the kernel):
- starch corn, soft corn: endosperm loose and very high in starch but low in protein, floury; primarily cultivated in South America; specially suitable for starch production
- dent corn: kernels similar in shape to a horse's tooth; absence of horny starch in the crown of the kernel; worldwide the most important corn; origin: America, Russia, south-eastern Europe
- flint corn: thick, horny upper layer of kernel, small, soft endosperm; particularly robust in an unfavorable climate
- popcorn: kernels almost completely consisting of horny starch, high in protein
- pearl popcorn: round kernels
- rice popcorn: pointed kernels, heating causes expansion and makes the husk burst. Origin: USA, Mexico, Hungary
- sweet corn: wrinkly, translucent kernel, very high in sugar, high fat and protein content. Origin: USA, south-eastern Europe
- waxy corn: kernel with a waxy appearance. Origin: Asia
Oil content: 4.2 - 5.4%.
Applications
Corn is used for flour production and as a feedstuff. Corn is the most calorific feedstuff and is used to feed, among others, chickens, laying hens and fattening pigs. Starch, margarine and edible oil are also obtained from corn.
Shipment/storage
Corn which is "dry for shipment" may be kept for up to 12 months or longer. For corn from the USA and Canada, a maximum water content of 15.5% (not an average value) is tolerated with an anticipated maximum voyage time of 3 weeks. If the critical water content is exceeded, mold growth occurs, especially in winter when voyages may last longer. Excessively moist corn has a sour odor. Predominantly transported as bulk cargo, rarely in bags (seed in security sealed bags).
Mainly in bulk containers, but also as bagged cargo (e.g. seed) in standard containers. Compliance with limits for the water content of the cargo and container floor must be ensured. In damp weather (rain, snow), the cargo must be protected from moisture, since wetting and extremely high relative humidities may lead to mold growth, spoilage and self-heating due to increased respiratory activity. Suction and blowing devices may cause not inconsiderable damage to the grains. Stow cool, dry, good ventilation.
Matting and jute coverings. If different types of cereal are stowed in the same hold, corn must be stowed on top because of its higher water content and need for more vigorous ventilation. When loading an ocean-going vessel with several types of cereal, heavy cereals (wheat, rye, barley, corn) must be stowed in the lower part of the hold and lighter cereals (oats, millet) in the upper part of the hold, for reasons of stability.
Temperature
Corn requires particular temperature, humidity/moisture and ventilated conditions. Favorable travel temperature range: no lower limit - 20°C. Molds reach optimum activity at temperatures of between 20 and 30°C. In addition, at temperatures > 25°C, metabolic processes increase, leading to increased CO2 production and self-heating of the corn. If the cargo is transported in a hot, moist storage climate, there is a risk of premature germination (premature sprouting). This is a particularly serious problem with seed corn. Maximum temperatures of 30°C are admissible for short periods.
Humidity/Moisture
| Designation | Humidity/water content |
| Relative Humidity | 70 - 75% |
| Water content | 11,5 - 14% |
| Maximum equilibrium moisture content | 75% |
The maximum admissible water content for corn before shipping is 14%. Mold growth occurs if the maximum water content is exceeded. This risk increases in winter, when voyages last longer. Excessively moist corn also has a tendency to ferment and acidify. This results in discoloration and mold. Storage under moist, hot conditions entails a risk of premature germination, which results in depreciation especially for seed corn.
Corn, like all other types of cereal, is also characterized by its hygroscopicity. The sorption isotherms for Argentinean corn show that corn which is dry for shipment with a maximum admissible water content of 14% prior to shipment is at equilibrium with a relative humidity of 65% at 20°C. At a water content of 15% it is at equilibrium with a relative humidity of 70%, i.e. still distinctly below the mold growth threshold. At higher temperatures, as in the country of origin Argentina, the water content must be correspondingly lower, for example 11.5 - 13%. The maximum admissible water content tolerated for corn from Canada is 15.5% if the temperatures are low and the duration of the voyage is at most 3 weeks.
Apart from testing moisture with a moisture meter, corn may also be tested organoleptically for its moisture content: a handful of corn kernels is pressed together by hand and if the kernels remain stuck together the corn is unsuitable for maritime transport. Corn may also be tested by cutting: if the center is soft, moist and loose, it is not dry for shipment. Since losses are inevitable with moist corn, it should not be accepted for shipment. Mats must be carefully laid, so that the corn cannot come into contact with metal parts of the ship or container.
Corn is among those goods which frequently arrive on board not dry for shipment, which can then result in considerable losses. It must also be noted on loading that hygroscopic goods can reabsorb moisture during storage in moist, tropical air. In areas with dry and rainy seasons, the shipment deadline must be noted. For example, if the outward transport of the cereal, which usually takes place in the dry season, is delayed into the rainy season, the water content on loading must be particularly carefully monitored as such late loading has been the cause of a series of losses.
Ventilation
Corn requires particular temperature, humidity/moisture and ventilation conditions. Recommended ventilation conditions: surface ventilation. Ventilation of cereals depends on water content: goods with a water content of < 14% and equilibrium moisture contents of < 70% do not need to be ventilated. Up to a water content of 15%, surface ventilation is recommended, in order to dissipate CO2, heat and moisture. At the same time, care should be taken to ensure that the surfaces are not cooled too much, to avoid the formation of damp boundary layers beneath the cargo surface.
Corn releases water vapor constantly, which needs to be dissipated by ventilation. However, caution is advisable on voyages from hot to cold regions (e.g. Argentina to Europe):
Corn which is not dry for shipment has a particular tendency to self-heating and the flow of heat from the cargo counteracts external cooling, so resulting in the formation of steep temperature gradients in the superficial layers of the cargo. At the same time, water vapor flows from the inside of the cargo to the surface. In the case of simultaneous cooling of the surface by ventilation, the relative humidity increases in the superficial layers of the cargo. If dry fresh air is used for ventilation, a dry surface layer several centimeters thick is obtained, which creates the impression that the cargo is free of all defects. Beneath this is then a damp intermediate layer of lower grade cereal which is starting to decompose, being stuck together and swollen. Such damp intermediate layers are observed relatively frequently.
In order to avoid cargo damage caused by such moist intermediate layers, the fresh air supply must be restricted when there is an excessive temperature differential between the cargo and the external temperature. Damage to only a proportion of a cargo of corn is indicative of the damaged proportion having been stored in a dead air zone, where it was inadequately ventilated. Damage may also be caused by the ships' lying in the roads at the port of destination for an extended period at low external temperatures. The cargo within the stack is, however, still at a higher temperature, resulting in water vapor transport towards the colder parts of the cargo close to the ship's side, where moisture damage may then occur. Such damage is often associated with the fact that ventilation is stopped when the ship is lying in the roads. Ventilation is, however, essential until the cargo has been unloaded from the ship.
It is essential to be aware of the fact that it is impossible to ensure proper airing throughout a bulk cargo of cereals. Even when ventilation is carried out, the relative humidity of the immobile air between the individual cereal grains is determined by the product's water content. For this reason, as mentioned above, drying-out caused by ventilation is generally only superficial. As a result, cereal loaded in an excessively moist state cannot be dried and protected from spoilage by a ship's ventilation installation.
Biotic activity
Corn displays 2nd order biotic activity. Corn kernels are living organs in which respiration processes predominate, because their supply of new nutrients has been cut off by separation from the parent plant. When transporting corn, account must be taken of the fact that it is a living vegetable product, the storage conditions of which should be such that its vital functions and metabolic processes are restricted in such a manner that losses of weight and utility value do not occur.
Gases
In corn, metabolic processes continue even after harvesting. The kernels absorb oxygen and excrete carbon dioxide (CO2). This excretion of carbon dioxide is of significance in various respects: if relatively large quantities of CO2 accumulate in the hold, the respiratory activity of the cereal will drop. In the case of cereal which is dry for shipment, hold air with an increased CO2 content does not have a negative impact on the quality of the cargo, indeed mold growth is inhibited. However, if corn is shipped in closed holds/containers at relatively high water contents, the cereal must be expected to change over from aerobic to anaerobic respiration due to the build-up of CO2, which means, among other things, that lactic acid bacteria, which are able to tolerate an anaerobic environment, can also develop. Due to their toxicity, the resultant fermentation products CO2 , lactic acid and alcohol have an impact on the grain germ, especially on seed cereal, which loses its ability to germinate if stored in an oxygen-depleted environment.
The ethylene sensitivity of corn may be classified as low. The rate of ethylene production is very low, being below 0.1 µl/kg*h.
Risk factors
Due to its oil content, corn, especially freshly harvested corn, has a strong tendency to become rancid and undergo self-heating. If the temperatures measured at the cargo rise to > 40°C, action must immediately be taken to reduce the temperature. If the temperatures exceed 60°C, an increased risk of fire must be assumed and appropriate action taken. Damage caused by self-heating results in considerable depreciation.
Odor
Active behavior: Corn has a slight, pleasant odor. Excessively moist corn has a sour odor.
Passive behavior: Corn, like other types of cereals, is highly sensitive to the absorption of foreign odors. Gases and aroma substances, such as sulfur dioxide (SO2), phenol and kerosene, are readily absorbed by the cereal. For this reason, holds must be completely odor-free and deodorization must not be carried out only immediately before loading. Corn (in bags) must not be stowed over wool because the kernels can absorb the wool's fatty odor.
Contamination
Active behavior: Corn produces dust during cargo handling and storage. There is a risk of dust explosion.
Passive behavior: Especially after the carriage of contaminating (coal, ore, cement), odor-tainting or pest-infested cargoes, fitness for loading must be carefully reestablished by cleaning, disinfection, deodorization and ventilation. An inspection certificate confirming fitness for loading should be provided. Possible contamination of the corn by common corn smut must be taken into account.
Mechanical influences
Extended storage in the country of production may result in agglomeration of the product under stack pressure.
Toxicity / Hazards to health
CO2 is evolved as a result of the respiratory activity of the cargo. Because of the possible oxygen shortage, the hold must be ventilated and a gas measurement performed before access to the hold is permitted. Corn rendered moldy by the mold Aspergillus flavus is toxic and no longer usable as a feedstuff. It may be particularly toxic for pigs, horses and goats.
Shrinkage/Shortage
Evaporation of intrinsic moisture content may result in a weight loss of up to 0.5%. Further losses may arise due to adhesion to the hold walls and dust formation during cargo handling.
Insect infestation / Diseases
Corn may be infested by the following cereal pests during storage and transport:
- by the granary weevil (Sitophilus granarius)
- by the cadelle beetle (Tenebroides mauretanicus)
- by the rust-red grain beetle (Cryptolestes ferrugineus)
- by the sawtoothed grain beetle (Oryzaephilus surinamensis)
- by the European grain moth (Nemapogon granellus)
- by the Angoumois cereal moth (Sitotroga cerealella)
Infestation with the Angoumois cereal moth imparts an unpleasant odor to the corn. Losses of up to 24% may arise from infestation by the Angoumois cereal moth. The chewing damage caused by the cereal pests brings about increased respiration in the cereal (hot spots) and this, associated with the metabolic activity of the pests themselves, promotes evolution of heat and moisture, which in turn provide favorable living conditions for molds and subsequently, at very high moisture levels, for bacterial growth.
Insect infestation may also result in self-heating which ultimately gives rise to depreciation and finally total loss. Inadequately cleaned warehouses, holds and containers are generally the root cause of insect infestation. Cereal is also at risk from rats and mice, which can act as disease vectors and contaminate the cereal. Common corn smut may be caused by the fungus Ustilago zeae. A certificate of origin and health is required.
Note:(Source including Transport Information Service of the GDV)