|Characteristics and fitness for container transport
The term "cereals" covers the grain fruits of cultivated grasses (wheat, rice, corn, barley, millet, oats (Fig. 112), rye etc.). As a rule, cereals are transported worldwide in bulk carriers, for instance from the USA, Canada, Argentina, India, Indonesia and Australia. Seed and malt etc. are also transported by container.
With a water content of 11.5 - 15% (see Tab. 1), cereals belong the water content class 2 (WCC 2). The sorption isotherms exhibit a continuous S-shaped profile. As living organs, cereals belong to the category of goods displaying 2nd order biotic activity (BA 2). Cereals require particular temperature, humidity/moisture and possibly ventilation conditions (SC VI). Cereals do not have any particular requirements as to ventilation conditions, if they are introduced into the container in a container dry state and the temperatures and relative humidities can be kept correspondingly low.
Table 19: Chemical composition of major types of cereal in % 
Seed cereal and malt are transported in bulk containers with appropriate predrying to approx. 12 - 13%. Should standard containers be provided, it is advisable to suspend liner bags of plastic fabric with integral nonwoven fabric in the containers to catch sweat.
The cargo is kept away from the container doors by four rectangular bars, which fit into the container's last pair of corrugations. Once the container has been loaded, the liner bag is closed by means of straps. The container is unpacked by cutting the liner bag open at the bottom and tipping the container.
Bagged seed and malt in particular are also transported in standard containers.
Ventilated containers are favorable, since they may be actively ventilated from outside in order to dissipate moisture and heat. They have to be loaded below deck, in order to allow ventilation to work effectively. This is also true of standard containers: on deck, extreme temperature gradients may occur, especially during winter in the northern hemisphere, which may lead to container sweat or cargo sweat.
The structure and chemical composition of the grain vary little between the different types of cereal (see Table 19). As far as structure is concerned, three constituents of the cereal grain are worthy of further consideration:
Carbohydrates, especially starch, are the main constituent of a cereal grain. However, when it comes to transport in bulk, standard and ventilated containers, it is the water content that is important. Although, at 11.5 - 15%, the water content is low compared to that of fruit and vegetables, it still plays a considerable part in the respiration processes of the seed cereal. When transporting cereals, it must be remembered that they are living, vegetable organisms whose ability to germinate must be retained. The hygroscopic properties of cereals were described in Section 10.2.2. Fig. 114 shows the most important sorption isotherms for cereals.
Respiration of the ripe cereal grain
The influence of temperature and water content on the respiration intensity of the cereal grain is illustrated in Fig. 115.
Curves 1 - 4 show the respiration intensity of wheat as a function of storage temperature and water content. The following conclusions may be drawn from this illustration:
After harvesting, cereals usually undergo 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 transported. However, if the water content of the cereal is low (< 13%), proper storage allows the sweat moisture to be absorbed by the air without the risk of mold growth. This sweating process lasts for approximately one to two months.
Composition of the ambient air
The excretion of carbon dioxide by respiring cereals is important from various standpoints. If relatively large quantities of carbon dioxide accumulate in the hold, the respiratory activity of the cereal will drop. In the case of cereal which is container dry, air with an increased carbon dioxide content does not have a negative impact on the quality of the cargo, indeed mold growth is inhibited.
Cereals are sensitive to the absorption of foreign odors. The considerable absorption capacity of the cereal grain results from its rough surface and the individual shells of the husk and seed coat, which communicate with the external air through cracks. One metric ton of rye has a total surface area of 64,000 m². The resultant large overall surface area explains the elevated odor sensitivity of cereal grains. Gases and aroma substances, such as sulfur dioxide, phenol and kerosene (strong smelling chemicals), are readily absorbed by the cereal. For this reason, containers must be completely odor-free. On the other hand, excessively wet rice, in particular, may spread a penetrating odor.
The evolution of heat and moisture by the seed cereal has the following consequences:
The seed, especially rye seed, must be carefully cleaned due to infestation with toxic ergot (see Figs. 116, 117).
|Contact | Site Map | Glossary | Bibliography | Legal Notice | Paper version|