Managing Grain Drying in High Moisture Conditions

Managing Grain Drying in High Moisture Conditions

Sept. 23, 2010

Q: Should I turn off my aeration fan when it is raining or when humidity is very high?

A: The answer depends on two considerations:

  1. Do you need to push air through the grain to remove built-up heat to slow the rate of deterioration?
     
  2. Would you be able to accomplish additional drying given the current moisture content of your grain and the temperature and relative humidity?

I have provided two tables to help you answer these questions. Both tables are taken from Grain Storage Tips published by the University of Minnesota.

Rule of Thumb

  1. The shelf life of aerated corn is reduced by about half for every 10° increase in temperature at a given moisture content. For example, the shelf life of corn at 17% moisture is reduced from 9.5 months to 5.3 months when the grain temperature increases from 40°F to 50°F.
     
  2. The shelf life of corn is reduced by about half for every 1% increase in moisture content. For example, the shelf life of aerated corn at 50°F goes from 8.9 months at 16% to 5.3 months at 17% moisture content.

The best you can do is to maintain the grain quality you currently have. There is nothing you can do to improve grain quality once it is lost. Each time you allow a little deterioration to occur, dry matter and grain quality are lost forever.

Table 1 shows the shelf life of corn under the stated range of grain temperature and grain moisture conditions. The shelf life is the time (months) corn can be stored — with periodic aeration to maintain the stated temperature in the grain mass — before one-half of one percent of the dry matter would be lost. That is considered the maximum dry matter loss you can suffer and still maintain the current market grade.

Corn that is not aerated to carry away temperature buildup in the grain is estimated to have a shelf life one-third as long as the estimates in the table. This is why I recommend continuous aeration, rain or shine, when grain moisture content is over 17% and grain temperature is over 50°F. If corn is less than 17% and at or below 40°F, you could begin intermittent aeration provided the grain is closely monitored. I recommend frequent aeration based on the equilibrium moisture values in Table 2 until the corn is dried to 15% and 40°F or less. The eventual target for grain held in storage through the months of October through February is 15% moisture and 30°F.

Table 2 shows the equilibrium moisture content under various temperature and relative humidity conditions. Think of it this way – the equilibrium moisture content is the driest grain moisture content achievable using natural (unheated) air under the stated conditions no matter how long you run the aeration system.

Tom Dorn
Extension Educator

 Table 1. Shelf life (months) for aerated shelled dent corn, based on 0.5% maximum dry matter loss.
 
 Corn Moisture Content
 Temp  13% 14% 15% 16% 17% 18%
 40  150  61  29  15  9.5  6.1
 50  84  34  16  8.9  5.3  3.5
 60  47  19  9.2  5.0  3.0  1.9
 70  26  11  5.2  2.8  1.7  1.1
 80  15  6  2.9  1.6  0.9  *
Table 2 Equilibrium moisture content (% wet basis) for crops exposed to air at various temperatures and relative humidities.
Relative Humidity
Temp F
20%
40%
60%
80%
C
W
SB
C
W
SB
C
W
SB
C
W
SB
40
9.2
8.5
4.6
11.9
11.7
8.1
14.5
14.6
11.5
17.9
10.8
16.0
50
8.5
8.2
4.2
11.2
11.3
7.8
13.8
14.2
11.2
17.3
17.4
15.7
60
7.9
7.9
3.9
10.6
11.0
7.5
13.3
13.7
11.0
16.8
16.9
15.4
70
7.3
7.7
3.6
10.0
10.7
7.2
12.7
13.3
10.7
16.3
16.5
15.2
80
6.7
7.5
3.3
9.6
10.4
6.9
12.3
13.0
10.4
15.9
16.0
15.0
C = yellow dent corn; W = hard red winter wheat; SB = soybeans