ISSUE 11 July 11, 2002
NATURAL AIR DRYING BARLEY
An airflow rate of 0.75 cfm/bu should dry 17% moisture barley in about 20 days during late July and August. This airflow rate should be considered the minimum for natural air drying barley and 17% moisture should be considered the maximum safe moisture content to assure that the barley dries before there is a quality loss.
Germination is critical for malting barley. Mold will grow on the germ of the seed and affect germination before mold is visible. The safe storage period, based on germination, for barley at 17% moisture and 68EF is about 35 days, but is only about 19 days at 78EF. At 18% moisture, the safe storage period is about 26 days at 68EF, but is only about 13 days at 78EF.
The allowable storage time for 17% moisture commercial grade cereal grains is estimated at about 40 days at 70E and 20 days at 80EF, which is just slightly longer than that allowed based on germination.. The period based on visible mold growth is about 70 days for 17% moisture barley at 77EF. Barley quality will be lost long before there is a visible mold problem.
Barley temperature in a drying bin will be approximately the average of the daily maximum and minimum plus about 3 to 5 degrees for the amount that the fan heats the air. The average temperature for July is about 72 degrees, so if the fan heats the air about 4 degrees, the air temperature entering the bin is expected to be about 76 degrees. As moisture is evaporated from the barley in the drying zone, the air is expected to cool about 5 to 7 degrees. Therefore, the wet barley temperature above the drying zone would be expected to be about 70EF when the average outdoor temperature is about 72 degrees.
Barley should be dried to about 12% moisture for long-term storage. This is the expected final moisture content for natural air drying barley during late July or early August.
The resistance to airflow through barley is some less than through wheat, so natural air drying systems sized to provide an airflow rate of 0.75 cfm/bu thorough wheat should provide that amount of airflow or slightly more through barley. For example, an inline centrifugal fan providing .8 cfm/bu through wheat should provide an airflow rate of about 0.9 cfm/bu through barley. A high speed centrifugal fan is expected to provide the same airflow rate, not more, through the barley and wheat due to the design of the fan.
Dr. Kenneth Hellevang, PE
Ag. Engineer-Post Harvest/Structures