As wheat harvest approaches, now is a good time to consider drying and storage options. A good place to start is by reviewing the equilibrium moisture content chart for soft red winter wheat below, which shows the limits of drying, as well as storage, over a range of average weather conditions in Kentucky throughout the year. See Harvesting, Drying and Storing Wheat (ID-125) for more information.
Implications for Drying
- Soft red winter wheat will reach the moisture levels shown in the chart when exposed to the corresponding temperature and humidity levels after sufficient time in the field or drying system.
- Drying time will depend on the airflow rate through grain, which in turn depends on the depth of wheat in a bin. The minimum drying rate for natural air drying is 1 cfm/bu, but this can take several weeks to dry the top layer–during which time spoilage can occur.
- For wheat, a maximum depth of 10-ft (for axial fans) or 16-ft (for centrifugal fans) is recommended to achieve the minimum drying airflow rate. Bin-specific airflow rates can be determined at this University of Minnesota website.
- When the relative humidity is above 80% (at night and on cloudy days), adding 5 degrees of heat will lower the humidity by 10 points and will speed drying.
Implications for Storage
- The air space between grain kernels in a bin will have the humidity indicated at the corresponding moisture and temperature. For example, 13% wheat at 80°F will have a relative humidity in the air space between kernels just below 70%, but when cooled to 40°F will have a relative humidity just below 60%.
- Mold growth is suppressed during storage when the environment is maintained at a relative humidity level of 65% or lower. For this reason, clean wheat in good condition should be held at 12.5% during the summer in Kentucky when the average monthly temperature in July and August is 80°F.
- Wheat should be cooled below 70°F as soon as possible (usually in September) if held into the fall, and about 10 degrees each month until it reaches 35-40°F in December.
- Fans should be sealed after the final cooling cycle to prevent wind-driven air currents from re-warming the grain in the bottom of the bin.
By Sam McNeill, Agricultural Engineer Extension Specialist
Kentucky Pest News 