The warm September temperatures may have helped with the grain harvest, but they also might have created conditions that can cause stored grain to deteriorate, North Dakota State University’s grain drying expert warns.

The optimum temperature for insect infestations and mold growth is about 80 degrees, according to Ken Hellevang, NDSU Extension Service agricultural engineer.

Insect reproduction is slowed at temperatures below about 70 degrees and insects are dormant below about 50 degrees.

The allowable storage time without mold growth is approximately doubled for each 10 degrees the grain is cooled. For example, the allowable storage time for 16 percent moisture content wheat is about 70 days at 70 degrees, about 120 days at 60 degrees and about 230 days at 50 degrees. The allowable storage time for 14 percent moisture malting barley, based on germination, is about 70 days at 80 degrees, 175 days at 70 degrees and 430 days at 60 degrees.

Producers need to remember that grain moisture content will increase near the top center of the grain due to moisture migration if the grain is about 20 degrees warmer than the average outdoor temperature, Hellevang says.

Stored grain should be cooled to the average outdoor temperature during the fall using aeration. Cooling time can be estimated by dividing 15 by the airflow rate. For example, about 75 hours of fan time is required to cool the grain using an airflow rate of 0.2 cubic feet per minute per bushel. Grain temperature eventually should be cooled to about 25 degrees for winter storage.

Hellevang recommends producers measure the grain moisture content to check the status of drying and to develop a storage plan. However, moisture meters normally are not accurate for grain temperatures below about 40 degrees. To obtain an accurate value, producers should warm the grain sample in a sealed plastic bag or other sealed container to room temperature before measuring the moisture content.

A drying zone that is a couple of feet thick moves from the bottom of the bin to the top during natural air drying. If the top is not dry, collect samples from other levels to determine the progress of the drying front.

Warming the air by about 5 degrees will permit producers to continue to dry wheat during October using a natural-air, low-temperature (NA/LT) drying system if the outdoor air temperature average is above 40 degrees. The moisture-holding capacity of the air at temperatures below about 40 degrees is small, so drying becomes inefficient using NA/LT drying. Adding more heat causes grain in the bottom of the bin to be dried to a moisture content lower than desired and changes the drying speed very little.

Drying speed primarily is dependent on the airflow rate. An airflow rate of 0.75 cubic feet per minute per bushel (cfm/bu) will dry wheat at moisture contents up to 17 percent. However, drying time will be about twice as long at 50 degrees as at 70 degrees. Drying can be completed in late April and May using natural air drying if the moisture content is 17 percent or less.

Use a bin-stirring device or do batch-in-bin drying with only a few feet of grain in the bin if the air is heated more than 5 to 10 degrees. If using a high-temperature dryer, limit the plenum temperature to prevent damaging the grain.

Dryer temperature will vary with dryer type, but a general recommended maximum air temperature for drying milling wheat in a continuous-flow dryer is 150 F for 16 percent moisture content and 130 F for 20 percent moisture content wheat. Hellevang also recommends limiting the plenum temperature in a high-temperature dryer to a maximum of 110 F when drying malting barley to maintain germination.

NDSU Agriculture Communication