NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

October 15, 1998

Engineer Says Cool Stored Grain to Maintain Quality

An early small grains harvest, warm September temperatures, and large quantities of stored grain combine to increase the potential for storage problems this year, according to a North Dakota State University agricultural engineer.

"More than for any other reason stored grain goes out of condition because grain temperature is not controlled," says Ken Hellevang of the NDSU Extension Service.

The ideal temperature for insect and mold growth in stored grain is about 80 F, Hellevang says. Cooling the grain below 50 F causes insects to become dormant and, if the grain is held at or below freezing during the winter, most insects will be killed. Mold growth is almost nonexistent at temperatures cooler than 40 F. The storage life of grain is approximately doubled by each 10 degrees that the grain is cooled.

Because moisture begins to migrate in stored grain when there is about a 20-degree temperature differential in the grain mass, aeration should start before the average outdoor temperature is 20 degrees cooler than the grain temperature, Hellevang advises. Typically the grain will be aerated shortly after harvest, once during the fall, and again probably in November as outdoor temperatures cool. The grain should be cooled to about 20 F to 30 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 cubic feet per minute per bushel. 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," Hellevang says. "The average daily humidity is what is important. Shut off aeration fans during periods of fog or rainy weather to minimize rewetting. However, if fans do operate during these periods the rewetting will be restricted to a relatively shallow layer of grain."

Hellevang advises producers to 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.

The condition of stored grain should be checked at least monthly, for moisture content and temperature, at several locations. "Recording the data will provide a for future reference for managing the stored grain," Hellevang says.

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Source: Ken Hellevang (701) 231-7243

Editor: Tom Jirik (701) 231-9629