Nebraska experienced good weather for harvesting and drying grain in fall 2011, allowing many producers to dry grain to a safe moisture content —15% for corn and 13% for soybeans — for winter storage.
"You also need to cool the grain as air temperature allowed," says Tom Dorn, University of Nebraska-Lincoln Extension educator in Lancaster County. "A rule of thumb is that at a given grain moisture content, the shelf life of corn almost doubles for every 10 degree drop in the temperature down to about 40°F. However, don't drop the grain temperature below freezing so you can provide additional aeration if we get a few days of warmer temperatures in February.
"If you didn't get your grain as dry as you wanted last fall and the forecast calls for a warm spell with low humidity, you may want to take advantage of the good weather and turn on the aeration fan to do more drying," Dorn says. "However, initially, you may actually add moisture content to the grain, depending on the grain temperature. For example, when air temperature is 50 degrees and the relative humidity is 50%, the dew point temperature is 32 degrees Likewise, if the air temperature is 50 degrees and the relative humidity is 60%, the dew point temperature is 37degrees. When the grain temperature is lower than the dew point temperature, air will condense moisture onto the grain until the air stream warms the grain mass above the dew point temperature."
If the grain temperature is below freezing, the condensation can be in the form of frost, which could add moisture to the grain and impede airflow through the grain.
Bins should be checked monthly in winter and spring, especially if high winds may have carried blowing snow into the bin. The danger is that the snow will melt and create a wet spot in the grain which could lead to spoilage and insect activity when warmer temperatures return in the spring.
When you check grain in a bin, open the access hatch, then start the aeration fan. Climb back up and lean into the access hatch as soon as possible after turning on the fan so you can feel and smell the air as it hits your face. You are looking for three things that could signal trouble.
Is the air warmer than expected?
Can you feel moisture on your face as you lean into the access hatch?
Is there condensation forming on the underside of the bin roof on a cold day?
If any of these three conditions occur, the fan(s) should run long enough to bring the entire grain mass to a uniformly cool temperature inside the bin. The best way to tell if the grain temperature is uniform is to use a grain thermometer that can be pushed three or four feet into the grain. Probe a couple of feet away from the bin wall, taking the temperature every 15 to 20 feet around the perimeter of the bin and at a minimum of three spots in the central part of the bin. If two spots differ in temperature by more than about 8 degrees, turn on the aeration fan and push air through the bin until a uniform temperature is reached throughout the grain mass.
If you didn't get the grain down to a safe storage moisture level in the fall and the grain was cooled to 30 degrees for safe keeping in winter, it will need to be warmed in stages to 40 degrees in late February or early March. This will allow you to take advantage of days with low humidity to finish drying the grain in the spring.
If you warmed the grain to do some additional drying but now the forecast is for unfavorable weather conditions, run the aeration fans at every opportunity to cool the grain again to reduce deterioration. Your goal should be to get the grain back down to 40 degrees.You can keep dry corn that will be held into April at 40 degrees. If corn will be kept into May or June, warm the grain to 60 degrees by May 1.