Management of stored grain with aeration
Figure 1. Moisture migration in grain stored without aeration
Aeration is the practice of moving air through stored grain to reduce the rate of grain deterioration and prevent storage losses. Spoilage in stored grain is caused by mold growth and insect activity, which is related to the moisture content and temperature of the stored grain. Aeration greatly improves the "storability" of grain by maintaining a cool, uniform temperature throughout the storage to reduce mold development and insect activity and to prevent moisture migration.
Temperature differences in a bin of stored grain cause moisture to migrate from warmer areas to colder areas. Figure 1 shows moisture migration in a bin when grain temperature differences are created due to colder weather. The warm air rising in the center of the bin cools when it reaches the cold grain near the surface. This results in moisture condensation near the surface and leads to rapid spoilage when the weather turns warmer. Crusting on the surface of stored grain is a common symptom of moisture migration. Moisture can also migrate to colder grain near the bin walls during cold winter weather. It is also possible to get moisture migration inward if the outside temperature is warmer than the grain. This is usually not as serious as the moisture migration upward and outward during cold winter weather.
Temperature differences can be caused by changes in outside temperature while the grain is being delivered to the bin. The temperature of corn delivered to storage from a high-temperature dryer will vary due to temperature changes throughout the day or with weather changes. Aeration is necessary to equalize and maintain uniform temperatures throughout the storage.
Effect of temperature on storability
The effect of temperature and moisture content on the allowable storage time of shelled corn is given in table 1.
Table 1. Maximum storage time in months for shelled corn*
|Corn temperature ° F||Corn moisture content|
|*Based on 0.5% maximum dry matter loss – calculated on the basis of USDA research at Iowa State University.|
The allowable storage times given in this table are based on deterioration of the grain associated with 0.5 percent dry matter loss. As shown, the deterioration rates depend on grain moisture content and grain temperature. Proper aeration maintains grain temperatures low enough to minimize grain deterioration. An illustration of the importance of proper aeration to the cash corn producer is to compare the "storability" of 15 percent corn at 50° F (16 months) to that of 15 percent corn at 70° F (5.2 months) and to 14 percent moisture corn at 70° F (11 months). These comparisons indicate the importance of maintaining uniformly low temperatures in all stored grain.
Table 2 shows the moisture content of various grains that can be stored in Minnesota for different lengths of time with good storage management.
Table 2. Storage moisture contents for aerated grain
|Shelled corn||Soybeans||Wheat and barley||Sunflowers|
|*Short term means until the following June.|
These moisture contents may be too high if the grain is poorly managed in storage. On the other hand, grain can be stored at higher moisture contents with exceptionally good management. If you have been successfully storing corn at 13 percent, do not attempt to increase to 15.5 percent in one step. Increase the moisture content to 14 percent and gain experience in storage management; then gradually work up to the desired level.
Aeration changes the temperature of stored grain in response to seasonal temperature changes and maintains uniform temperatures throughout the storage. Aeration is not a grain drying system and must not be considered as such. Some changes in grain moisture content occur as a result of aeration. The heat removed during cooling results in some drying. Grain moisture content will be reduced about one-fourth percent for each 10° F reduction in temperature. Little moisture change results from the drying or rewetting capacity of the small amounts of air necessary for changing the temperature of the grain. However, significant changes in moisture content can occur if substantially more air is moved through the grain than is required for a temperature change. This can happen when high airflows are used for extended periods beyond that necessary for changing the grain temperature.