~by Greg Brenneman – ISU ag engineering specialist
It is important to keep stored grain as cool as we go into the spring and summer months. Some warming of stored grain may have already occurred during warmer weather and with the sun shining on the south side of grain bins.
With the weather forecast for Friday through next Tuesday to have highs in the 30s and low 40s with lows in the 20s, this may be the last good time to completely aerate your stored grain before warmer spring weather arrives.
Ideally, we would like to keep stored grain temperatures below 40 degrees going into the summer months. By keeping grain as cool as possible, we can limit insect activity and the growth of spoilage molds.
Remember, it only takes about 15 hours for a large drying fan (1 hp per 1000 bu) to completely change the temperature of the grain in a full bin. However, as small aeration fan (1/10 hp per 1000 bu) may take 5-6 days to completely cool a full bin. Keep a close eye on the fans and the weather so you don’t inadvertently warm it back up when temps increase next week.
Some corn went into storage late last fall in the 15 to 16 percent range as it came out of the field. It is important to get this corn moved or dried before going into the summer months.
To store grain safely during the summer, the maximum moisture content is 13 to 14 percent for corn and 11 percent for soybeans. Mold growth will occur at summer temperatures if the grain exceeds these moisture contents. The allowable storage time for 15 percent moisture corn is about four months at 70 degrees and only about two months at 80 degrees.
Because grain is a good insulator, during the summer most warming will occur at the surface of the grain. Provide an air inlet near the bin roof eave and an outlet near the peak to reduce the hot air in the top of the bin. Similar to venting an attic, the heated air rises and is exhausted at the peak. A ventilation fan to exhaust the hot air from the top of the bin is another option.
During the summer months, Ken Hellevang, North Dakota State ag engineer, suggests running the aeration fan for a few hours to push air up through the cool stored grain to cool grain near the top. Pick a cool morning every two to three weeks during the summer to run the aeration fan, and only run the fan a few hours to minimize heating grain at the bottom of the bin.
Cover aeration fans when they are not operating to prevent additional heating of the grain. The wind and a natural chimney effect will push warm, moist spring air through the grain warming it and possibly adding some moisture.
