Keep Stored Grain Cool, Dry During Summer
Stored grain needs to be cool and dry during summer storage, a North Dakota
State University Extension Service grain-drying expert says.
“Cold or cool grain has been safely stored through the summer for many years,”
notes Ken Hellevang, an Extension agricultural engineer. “Keeping the grain as
cool as possible should be the goal of summer grain storage.”
Allowing grain to warm to average outdoor air temperatures during the summer can
lead to insect infestations and mold growth. The optimum grain temperature for
insect activity is approximately 70 to 90 degrees. Reducing grain temperatures
below 70 degrees will lessen insect reproduction and activity, and temperatures
below 60 degrees will reduce insect activity greatly.
Aeration fans should be covered to prevent wind and a natural chimney effect
from warming the grain. Wind blowing into uncovered fans or ducts will move air
through the grain in a way that is similar to operating an aeration fan.
Hellevang warns that using aeration to warm the grain increases its moisture
content by up to 1 percentage point.
Good Bin Roof Ventilation Important
One challenge to keeping the grain cool during the summer is that solar energy
on the bin roof heats the air above the grain. Convection currents in the grain
flow up along the bin wall and down into the grain near the top middle of the
bin, drawing this heated air into the grain. Ventilating the space between the
grain and the bin roof can reduce the amount that the grain near the top of the
bin is warmed.
Natural ventilation to cool this space can occur if the bin has openings near
the eave and peak; these openings work like the vents in a building’s attic. The
heated air rises and exits near the peak, drawing in cooler air near the eave.
This natural ventilation will not occur unless the bin has adequate openings at
the eave and peak. Roof exhaust fans controlled by a thermostat also can draw
the heated air out of the bin if openings are available to allow air into the
area above the grain.
When to Use Aeration
Hellevang recommends cooling grain in the upper portion of the bin by operating
the aeration fan about every three weeks during a cool morning. Using
positive-pressure aeration to push air up through the grain enables the cool
grain in the bottom of the bin to cool the air, which then cools the grain near
the top of the bin.
Run the fan only long enough to cool the grain near the top surface. That may
require running the fan for a few hours during a cool, dry morning for a couple
of days. Running the fan more than necessary will warm more grain at the bottom
of the bin, increasing the potential for storage problems.
If the air dew point is warmer than the grain temperature or if the air relative
humidity is very high, some moisture will condense onto the grain during fan
operation. Condensing moisture will release heat that will warm the air
slightly, reducing the effectiveness of the aeration. The grain moisture content
increase is typically less than 1 percentage point because the grain warms and
is no longer cool enough to cause moisture to condense onto the grain.
Therefore, select mornings when the air is cool and dry.
Unload Some Grain
Some people unload some of the grain periodically during the summer to remove
the warmed grain at the top. The grain unloads in a funnel shape in bins with a
center sump, with the grain from the top flowing down to the unloading sump at
the bottom of the bin.
Removing peaked grain reduces the potential for grain warming at the top of the
bin. A cone-shaped peak has a larger ratio of surface area to grain quantity,
which leads to more grain warming than occurs with leveled grain. In addition,
because air takes the path of least resistance, the aeration airflow will be
near the bin walls, with little airflow through the peak. This makes the peak
difficult to cool.
Summer Moisture Recommendations
Verify that the grain moisture content is dry enough for storage at summer
temperatures. The recommended long-term storage moisture contents are: wheat,
13.5 percent; barley, 12 percent; corn, 13.5 percent; soybeans, 11 percent;
grain sorghum, 13 percent; oil sunflowers, 8 percent; and confectionary
sunflowers, 10 percent. The market moisture content may be higher, but storing
warm grain at higher moisture contents may lead to mold growth on the grain.
Make sure the moisture content measured by the meter has been adjusted for grain
temperature. Confirm the accuracy of the measurement by warming the grain sample
to room temperature in a sealed plastic bag before measuring the moisture
Grain Storage Time
Grain storage life depends on the grain’s moisture content and temperature. The
allowable storage time is cumulative, so if half of the life is used since
harvest, only half remains for the rest of the storage period. This is
particularly crucial for grain being stored into late summer or for more than a
Each 10 degrees the grain temperature increases reduces the allowable storage
time (AST) by about half. For example, the AST for 15 percent moisture corn is
only about 70 days at 80 F. The AST increases to 125 days at 70 F and 240 days
at 60 F. This emphasizes the importance of keeping the grain as cool as possible
during the summer.
The AST typically increases by 50 to 75 percent for each percentage point
reduction in grain moisture content, depending on grain moisture and
temperature. For example, the approximate storage life of 15 percent moisture
corn at 70 degrees is about 125 days. The AST increases to about 200 days at 14
However, that is only about 4.7 months, so if corn is stored at 14 percent
moisture and 80 degrees during the summer, little storage time remains. This
stresses the importance of controlling grain moisture content and temperature.
Where to Measure Grain Temperature
Measure and record the stored grain temperature at several places near the top
surface, along the walls and within the grain. Temperature sensors are an
excellent tool when monitoring stored grain, but remember that they only measure
the grain’s temperature next to the sensor. Because grain is a good insulator,
the grain temperature may be much different just a few feet from the sensor.
Increasing grain temperature may be an indicator of an insect infestation or
“Mold growth and insect infestations occur rapidly at summer temperatures, so
stored grain should be checked every two weeks,” Hellevang says. “A situation
with only a few insects can turn into a major infestation in less than a month.
Using insect traps or placing grain samples on white material helps you look for