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Cool Stored Grain to Prevent Damage
The ideal temperature for insect and mold growth in stored grain is about 80 F. Cooling the grain below 70 F reduces insect reproduction, cooling it below 50 F causes insects to become dormant and, if the grain is held at or below freezing during the winter storage period, many insects will be killed. Mold growth is almost nil at temperatures below 40 F.
Because about 1 20-degree temperature differential in the grain mass will cause moisture migration, aeration should start before the average outdoor temperature is 20 degrees cooler than the grain temperature. Typically, grain will be aerated shortly after harvest, once during the fall, and again probably in November as outdoor temperatures cool. Grain should be cooled to about 20 F to 25 F degrees for winter storage.
The amount of time required for an aeration cooling cycle depends on the airflow rate. The cooling time can be estimated by dividing 15 by the airflow rate. For example, about 75 hours is needed with an airflow rate of 0.2 cfm/bu. Check the grain temperature at several locations to determine when the aeration cycle is complete.
Grain temperature changes about 50 times faster than the moisture content, so the relative humidity of the air is of little concern during grain cooling. The average daily humidity is what is important. Shut off aeration fans during periods of fog or rainy weather to minimize rewetting. If fans operate during these periods the rewetting will be restricted to a relatively shallow layer of grain.
Cover fans and ducts after the grain has been cooled for winter storage to prevent snow from blowing into the grain bin. It is best to cover the fan whenever it is not running to prevent rewetting grain during wet weather.
Check the condition of stored grain every two to four weeks. A check should include measurements of moisture content and temperature at several locations. Moisture measurement accuracy is dependent on the grain temperature, so it is best to collect a grain sample, let it warm to room temperature in a plastic bag or other sealed container, then check the moisture content. Record the data for future reference in managing stored grain.
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