February 5, 2010
If your bin of corn is at or below 15% moisture, monitor for signs of heating twice a month.
To determine the hours needed to push a temperature front through a bin of grain, divide 15 by the airflow in cubic feet per minute per bushel in the bin (cfm/bu).For example, if your drying fan can produce 1.0 cfm/bu, it will take about 15 hours. If you have a storage bin with a small fan producing 0.2 cfm/bu, it will take 75 hours.
If you have a grain temperature probe, take the grain temperature near the bin wall about every 20 feet around the outside of the bin and a couple of places near the middle of the bin. Let the probe stay in place for 7 to 10 minutes before taking each reading. If there is more than a 10 degree difference in temperature between any two spots in the bin, run the aeration fan long enough to push a temperature front through the entire grain mass.
If you don't have a temperature probe, test for signs of heating by turning on the aeration fan and leaning into the access hatch or climb into the bin.
- Does the air hitting your face feel warmer than expected?
- Do you detect a musty odor?
- Does condensation form on the inside surface of the bin roof on a cold day?
If you detect any of these symptoms, continue to run the fan long enough to push a temperature front through the bin. If the bin is equipped with a stirring system, run two or three rounds to break up hot spots and equalize the moisture throughout the grain mass. If the warning signs are present and the bin is not equipped with a stirring system, pull a load or two out of the bin and monitor the condition of the grain coming out of the auger. If you detect heating, run the aeration fans to cool and dry the grain if air properties allow. Level the grain surface if the remaining grain will be left in place.
If the corn is above 15% moisture and you plan to continue holding the grain on the farm, prepare to finish drying it to a safe moisture content.
The first objective is to warm grain that was cooled in late fall to preserve it during the cold months. Grain should be warmed in stages. Run a warming front through the bin when the outside air temperature is 10 to 12 degrees higher than the grain temperature. When the grain is above 40°F, use the Equilibrium Moisture Content table to judge when to run the aeration fan to dry the corn. The values in Table 1 are the driest moisture content achievable under the conditions.
Tom Dorn
UNL Extension Educator, Lancaster County
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Table 1. Equilibrium moisture content of shelled corn at various air temperatures and related humidities. |
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Air Temp |
Relative Humidity | |||||
|
50% |
55% |
60% |
65% |
70% |
75% |
|
|
30 |
13 |
13.5 |
14.5 |
15.5 |
16.5 |
17.6 |
|
40 |
12.5 |
13.0 |
13.8 |
14.7 |
15.5 |
16.5 |
|
50 |
12.0 |
12.5 |
13.3 |
14.0 |
14.8 |
15.8 |
|
60 |
11.4 |
12.0 |
12.6 |
13.4 |
14.0 |
15.0 |
|
80 |
10.4 |
11.0 |
11.6 |
12.2 |
13.0 |
14.0 |
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Based on USDA research at Iowa State University |
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