Wednesday, June 18, 2014

Drying the 2014 Wheat Crop

Sam McNeill, Extension Agricultural Engineer, University of Kentucky
The delay in wheat maturity and concern for late planting of double crop soybeans provides motivation to consider drying wheat this spring.  When to start harvest will depend on the drying system, with typical ranges shown in Table 1. Operators with little experience should start at low moisture levels and ramp up as they gain experience. Use a moisture meter to check grain conditions in the field and during drying, and dry to 13.5 if holding for a few weeks or 12.5% when holding through the summer. Drying air temperatures should be limited to 140 o F for food grade wheat and 110o F if used for seed.
Drying system
Wheat moisture, %wb
Bins with large fans but no heater
< 17
Bins with large fans with heat or stirring augers
17 to 20
High temperature bin, batch or continuous flow dryers
20 to 24

A minimum of one cubic feet of air per minute for each bushel (1 cfm/bu) is needed for bin dryers without heat. The FANS program from the University of Minnesota Biosystems Engineering Department is the best way to determine the amount of airflow for specific bin-fan combinations (http://webapps.bbe.umn.edu/fans/).  For example, a 30-ft bin with a 10 horsepower axial fan can deliver 1 cfm/bu at a depth of 10 feet (5700 bushels), or a 15 hp centrifugal fan can deliver the same airflow at 14 ft (8000 bushels). Natural air drying requires 2 to 3 weeks of continuous fan operation, during which time wheat will dry to the levels shown in Table 2 for the prevailing average temperature and relative humidity conditions. For example, the average conditions for June in Kentucky (70 degrees and 65% humidity), will dry wheat to 12.8%.

Table 2. Equilibrium moisture content (EMC) of soft red winter wheat at different temperature and relative humidity levels. Source: ASABE Standard D245.4.)
Relative Humidity (%)
Temperature
10
20
30
40
50
60
65
70
80
90
°F
Equilibrium Grain Moisture Content (%)
  35
7.3
8.9
10.2
11.3
12.3
13.4
14.0
14.7
16.1
18.2
  40
7.1
8.7
10.0
11.1
12.1
13.2
13.8
14.4
15.9
18.0
  50
6.8
8.4
  9.6
10.7
11.8
12.9
13.4
14.1
15.5
17.6
  60
6.5
8.1
    9.3
10.4
11.4
12.5
13.1
13.7
15.1
17.2
  70
6.2
7.8
 9.0
10.1
11.1
12.2
12.8
13.4
14.8
16.9
  80
6.0
7.5
 8.7
 9.8
10.8
11.9
12.5
13.1
14.5
16.6
  90
5.8
7.3
 8.5
 9.6
10.6
11.6
12.2
12.8
14.2
16.3
100
5.6
7.1
 8.3
 9.3
10.3
11.4
12.0
12.6
14.0
16.0

A small amount of heat (10 degrees) is needed when bin-drying wheat over 17% moisture and the outside humidity is above 90%. Reduce or eliminate heat when the humidity is below 70%, otherwise the bottom layer will be over dried and profits will erode (7 cents per point of moisture for $6 wheat). Limit depths to provide 2 or 3 cfm/bu and dry in layers before adding more wet wheat in the bin.

High temperature dryers usually have excess fan and heat capacity for drying wheat above 20% moisture. Drying air temperature can be regulated by cycling the burner on and off or by changing the gas burner orifice with one designed to operate at low temperatures. Aeration should be used to cool wheat after drying with heated air. To a small degree, aeration will control grain temperature if it starts heating during storage, but this may only be a short term solution to avoid further damage. If heating cannot be controlled by running the fan, the crop should be moved to another bin to break up hot spots that usually cause the problem. Consider adding temperature cables to monitor conditions during storage and an automated controller for aeration fans to start cooling stored wheat below 60o F as soon as possible in late summer.

Check the condition of stored wheat once a week during warm weather to protect it from insect activity. Run the fan for a few minutes to check for off odors from the grain pile. Lock out unloading auger motor switches before looking inside any bin to check the grain surface. Feel the top 6 to 12 inches of wheat to monitor temperatures and insect activity. Insert plastic pit traps below the grain surface (being sure to secure them to the ladder) to monitor insect activity and check them during weekly inspections to stay ahead of damaging populations. Always wear dust protection masks when cleaning bins as well as during an inspection. The UK Entomology Department provides annual updates on approved insecticides for protecting stored wheat (http://www.ca.uky.edu/entomology/entfacts/ef145.asp). More information on drying and storing wheat is provided in UK ID-125 (http://www.ca.uky.edu/agc/pubs/id/id125/id125.pdf).


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