09/16/2014

Natural Air Drying Tips

1. When Can I Begin to Harvest?

With a complete Grain Guard system in place, crops can be taken off at 4% - 6% moisture above the level they would normally be harvested at (example: wheat 18% - 20%). Under warm, low relative humidity conditions you should see 3/4 - 1% of drying taking place per day. This allows a 7-10 day advance on harvest time as well as more harvesting hours per day.

NOTE: Natural air drying should be used as a management tool and not as a late harvest emergency drying system. Late harvest conditions are cool and damp and will result in slow natural air drying. Monitoring the condition of the stored grain is required during the process.

2. At What Temperature Does Natural Air Drying Begin?

Grain drying begins at +10 degrees celsius (50 degrees fahrenheit). Anything less than +10 degrees celsius means the air is too cold and can only hold a small amount of moisture, therefore moisture movement from grain will be very slow.

3. When Should I Start My Fan?

In order to create a uniform drying front, you must have the height of at least half of the bin's diameter above the aeration system. (Example: 14' diameter bin needs to have a minimum of 7' of grain above the aeration system).

The best uniform drying front can be produced by filling your bin and then turning on the fan. Turning your fan on too soon can cause uneven drying, wet pockets and negative results.

4. Should I Shut My Fan Off at Night or When it Rains?

No! High moisture grain drying (16% - 20%), requires continuous air flow to prevent the drying front from crusting over and restricting the airflow.

How it works

5. Does Fan Operation at Night or in High Humidity Conditions Reverse the Drying Process?

We tend to think that a fan will force moisture back into a bin in high humidity conditions. However, it is much more difficult to put moisture back into the grain than it is to take it out. In fact, grain in the bottom of the bin which may be a little over-dried would benefit from taking on a little moisture.

At 19% moisture, grain that hasn't been dried will remain constant as the 86% relative humidity moisture level in the air equals the moisture in the grain.

Relative Humidity     Wheat Equilibrium       Canola Equilibrium      
        of Air %              Moisture Content         Moisture content    
                                    at 25ºC at 10ºC                at 25ºC at 10ºC 

         58                           12       13                        7.5       8.6 
         64                           13       14                        8.2       9.4 
         70                           14       15                        9.0       10.3 
         75                           15       16                        9.8       11.1 
         79                           16       17                      10.8       12.0 
         83                           17       18                      12.0       13.2 
         86                           18       19                      13.4       14.5

6. If I Add Supplemental Heat, Can I Dry in High Humidity Conditions?

Adding supplemental heat to the aeration/drying process will reduce relative humidity and increase the rate of moisture movement. Therefore, a low temperature supplemental heater will increase the drying rate and reduce the drying time.

7. Can Low Temperature Supplemental Heat Cut My Drying Time Without Increasing Costs?

A rule of thumb relating temperature increase to relative humidity decrease is: A temperature increase of 10 degrees Celsius (18 degrees Fahrenheit) above outside air temperature will reduce the relative humidity by half.

Example: 10 degrees Celsius and 70% relative humidity 
+ 10 degrees Celsius (increased by supplemental heat) 
= 20 degrees Celsius and 35% relative humidity

When low temperature heat is added in high humidity conditions, drying times can be reduced up to 8 days. By reducing operating time, over-all costs are less than operating only the fan under these conditions.
With the average harvest period generally 30 - 40 days, it's comforting to know you can depend on supplemental heat - not the weather - to get the job done.

NOTE: Care should be taken when operating a supplemental heater under low humidity conditions. This can cause severe over-drying in the bottom of the bin.

8. How Do I Know When My Grain is Dry?

(Approximate drying chart based on a complete Grain Guard System)

Approximate Condition                       Approximate Drying %

Ideal warm days/dry conditions                        1% per day  
Warm days and cool nights                          1/2% per day  
Cool days and cool damp nights                   1/4% per day 
Cold days and cold nights                               0% per day  
Warm days and cool nights
(supplemental heat added)                           3/4% per day

  • If you add 1 or 2 loads of grain at 18% moisture into the bin, assume the bin to be at 18% average moisture - don't reduce the average if some loads are at a lower percentage.
  • Do not count the first day in the drying process as it takes 14 - 16 hours for the bin to equalize its temperature.

9. When Should I Shut My Fan Off?

When bin samples show the grain is dry, turn off the fan.

10. What Can I Do When the Air Temperature Does Not Reach +10 Degrees Celsius? (late October - early November)

There are a few options available at this point:

A.  You can dry the grain in a grain dryer and then cool it down with the Grain Guard system to maximize the grain dryer daily output.

B.  You can wait until the outside air temperature falls to -5 to -10 degrees Celsius and then run the fan for 24 - 48 hours to cool the entire grain mass to a storage state. Once spring conditions return, you can resume the grain aeration/drying process.