The quality of feed is mainly determined by the grain component which is the biggest ingredient. Grain quality is dependent on the harvested quality but must be maintained over the storage period to avoid deterioration. Corn because of its high energy content is usually the main feed grain, which is also one of the most critical crops that bring constraints to keeping feed quality. Its critical effects on the feed are not only caused by respiration, moisture migration, and risk of weevil infestation but its nature along with grain handling, leading to the main problem for feed, the fungus infestation, and mycotoxin contamination.
Nature of corn
Corn is a critical crop. The diversity of kernel size along with the wide range of moisture
content, and the kernel’s density make it inhomogeneous. The literature describes a moisture variation of +/- 2-5% and kernel sizes from 2-10 mm are common, affecting the bulk handling and bringing an alert for grain management. Usually, the industry considers only the average moisture content as an important factor. A crop of 14% moisture content is safe, but indeed for corn, it leads to a moisture variation of at least 12-16% or worse up to 25%. This defines the danger of safe grain storage which is highly different from general consideration.
Physics of bulk handling
The standard procedure of grain handling as a bulk is to load into and unload it from the storage silos. This dynamic of movement leads to a consequence that should be well understood as it is leading to critical conditions at the bulk storage.
While loading a crop into bulk storage, grains fall from the height of the loading point into the empty space. Thereby the kernels develop their individual movement according to the physics of gravity. The bigger the kernel or the denser, the more kinetic energy is developed during the fall. Accordingly, the energy must be released before the kernels find their final location at the storage facility. The higher the kinetic energy is, the longer the kernels move to a location from where they can’t move further. The wall of the bulk storage acts as a barrier stopping kernels. The consequence is that big, dense, and moist kernels accumulate there while small, light, and dry kernels remain at the center of the loading point as shown in Figure 1.
The accumulation of critical crops like corn along the silo wall creates a spoiling condition
leading to deterioration by high respiration, fungus infestation, and mycotoxin development. The following unloading of the grain further increases the risk of losing grain quality. Thereby the physics of unloading the grain is a determining factor of the quality of grains for feed production. Shown in Figure 2.
The grain following the unloading gate develops an unloading funnel which is usually at the center of a silo. The funnel consistently remains during the unloading and determines what grain will be unloaded first. Usually, light grain flows easily at the center exiting the silo first. The heavy, mist, and dense kernels being close to the silo wall remain longer inside the silo. The result is a longer retention time inside the silo under a condition that can’t be managed effectively by grain management. That leads to further deterioration till the grain is out of the silo. Usually, the last 10-20% of grains in bulk storage capacity is of lower quality, which is a known phenomenon, managers mix this with good-quality grain.
Fungus infestation of grains
The described situation of bulk storage of grains, in particular corn, leads to the usual experience of increasing fungus infestation during storage in a combination of high mycotoxin levels. Looking at the condition for fungus development is easy to understand in Figure 3.
The moisture content of grains, the temperature, and the relative humidity of the environment inside the storage determine the fungal development. Often storage conditions are 14% moisture content, temperature around 20-33°C, or relative humidity above 65% resulting in mycotoxin contamination. Reducing the temperature during storage will prevent fungus and mycotoxin development as indicated by the blue area in Figure 3.
Solution of advanced storage management of grain
Storage management is responsible to maintain the quality of the grain before processing
and to keep losses at a minimum. Common techniques include aeration, fumigation, and moving grains to avoid any damage from heat, insects, or fungus. All these technologies are widely used in the industry but have challenges regarding the ambient condition and the infrastructure of the storage. Good expertise is required to apply them effectively but often their effectiveness is limited or even fails. Therefore, it is worth looking into advanced bulk storage management by grain cooling.
The concept of grain cooling
The grain cooler is connected to the grain storage and conditioned air is blown into the bulk. The airflow passes the grains and removes the heat and excess moisture content of grains. Grain cooling continues until the entire bulk is cooled to a desired temperature of around 10-18°C depending on the intended storage time. Then the grain cooler is turned off and the air inlet and vent openings are closed. The cooled grain is kept in storage until unloading or refreshing again if there is a temperature rise during storage. The principle of the application is shown in Figure 4.
Conclusions
Grain cooling is a comprehensive solution for postharvest management that preserves a grain bulk. It keeps quantity and quality for processing of grains in the most economic condition. The implementation of technology in warm and humid climates leads to an essential improvement in grain handling, loss reduction, and good management practice, which has been proven already for more than 60 years.
By Dr Claus M. Braunbeck and Ralph E. Kolb, FrigorTec GmbH
