By Sara Bauder
As the average outdoor temperature begins to rise, stored grains are warming as well. Due to a difficult, wet harvest last fall and a challenging marketing situation, many producers in the region chose to store grains wetter and longer than typical. As a result, special care needs to be taken when storing these grains as the air temperature rises into the summer months.
Storage Temperature and Moisture Levels
Grain bins work as solar heat collectors, and the grain inside of them may be much warmer than expected. As the weather changes in the spring, keeping stored grain as cool as possible should be a producer’s goal. It is ideal to keep higher moisture grains near or below 30°F during the spring season until grain reaches recommended storage moisture levels (Table 1). After grain is adequately dried, it should be kept at or below 40°F through the rest of spring and early summer or as long as feasible. Throughout mid to late summer, it is best to keep the storage temperature for dried grain below 60°F if possible, which limits insect activity and potential mold issues. See Table 2 for an explanation of approximate allowable storage time of cereal grains; remember that allowable storage time is cumulative, so fall temperature and moisture have a large impact on spring storability.
Allowable storage time’ is considered the time before quality grain loss is expected. Airflow may help maintain grain temperature but will not extend allowable storage time. Allowable storage time listed in this table is cumulative, for example: if 20% moisture corn were stored for 25 days at 50°F, ½ of the storage life has been used. If the corn is cooled to 40°F, the allowable storage time at 40°F is only 45 days.
TABLE 1. MAXIMUM RECOMMENDED MOISTURE CONTENT
FOR WARM-SEASON GRAIN STORAGE
| Crop | % Moisture |
|---|
| Corn | 13-14% |
| Soybean | 11% |
| Wheat | 13.5% |
| Oil Sunflowers | 8% |
TABLE 2. APPROXIMATE ALLOWABLE STORAGE TIME FOR CEREAL GRAINS.
| Grain Temperature (°F) | 30° | 40° | 50° | 60° | 70° | 80° |
|---|
| Moisture Content (%) | Approximate Allowable Storage Time (Days) |
| 14 | * | * | * | * | 200 | 140 |
| 15 | * | * | * | 240 | 125 | 70 |
| 16 | * | * | 230 | 120 | 70 | 40 |
| 17 | * | 280 | 130 | 75 | 45 | 20 |
| 18 | * | 200 | 90 | 50 | 30 | 15 |
| 19 | * | 140 | 70 | 35 | 20 | 10 |
| 20 | * | 90 | 50 | 25 | 14 | 7 |
| 22 | 190 | 60 | 30 | 15 | 8 | 3 |
| 24 | 130 | 40 | 15 | 10 | 6 | 2 |
| 26 | 90 | 35 | 12 | 8 | 5 | 2 |
| 28 | 70 | 30 | 10 | 7 | 4 | 2 |
| 30 | 60 | 25 | 5 | 5 | 3 | 1 |
Adapted from “Approximate” Allowable Storage Timefor Cereal Grains.
Spring and Summer Storage Tips
- Cover bin aeration fans when not in use. Fans essentially go through the ‘chimney effect’ where wind moves wet, warm air into the fan and it travels upwards, affecting the grain inside.
- Provide an inlet for air near the roof eave and outlet exhaust near the roof peak to allow warm air to exit the bin (much like the principles of an attic). Several vents at the same elevation can still allow heat to remain at the top of the bin without exhaust at the peak or roof exhaust fans.
- Add a temperature sensor near the south wall of the bin to collect readings or be sure to take some grain samples from this area, which is likely the warmest part of the bin.
- Periodically run bin fans throughout the spring to help keep grain cool and slow warm up.
- During summer months, choose cool mornings every 2-3 weeks to run the aeration fan to keep grain cool and push cool air up through warm grain near the top of the bin.
- Run the fan only long enough to cool the grain at the top of the bin; this may mean running fans for a couple hours on more than one cool, dry morning. However, running fans more than necessary could result in grain warming near the bottom of the bin.
- Unload some grain. By unloading grain in bins with center sumps, warm grain from the top of the bin is unloaded first, leaving a funnel shape in the center of the stored grain. This can help to reduce grain temperature near the top of the bin and eliminate cone-shaped peaks (which lead to excess grain warming).
Measuring Grain Temperature and Moisture
Throughout grain storage, but especially during the spring and summer months, producers should check stored grain every week for storage temperature, insect infestations, and mold growth. Grain temperature should be measured at several places along the walls of the bin, near the top surface, and within the grain. Temperature sensors are very useful for this, however multiple readings are necessary to get an accurate picture of overall temperature. When using a moisture meter to check grain, be sure to warm up samples to room temperature in a sealed container for several hours before measuring.
Recommended Airflow Rates
The following recommendations are from Dr. Ken Hellevang, with NDSU Extension.
- Corn – The fans airflow rate should be at least 1 cubic foot per minute per bushel (cfm/bu) and the initial grain moisture should not exceed 21%. Start the fan when the outdoor temperature averages about 40 degrees.
- Soybeans - Use an airflow rate of at least 1 cfm/bu to natural air-dry up to 15-16% moisture soybeans. Start the fan when the outdoor temperature averages about 40 degrees.
- Wheat - Use an airflow rate of at least 0.75 cfm/bu to natural air-dry up to 17% moisture wheat. Start drying when the outside air temperature averages about 50 degrees.
- Sunflowers - Natural air-drying for oil sunflowers requires an airflow rate of 0.75 cfm/bu for up to 15% moisture. The drying should start when outdoor temperatures average about 40 degrees.
- For more information on selecting fans and determining if your fan is large enough, see the University of Minnesota Extensions’ Fan Selection Tool.
Source : sdstate.edu