Storing grain safely into summer (and beyond!)

In these uncertain times, farmers with grain still in the bin may be considering storing that grain a bit longer than they’d originally expected.  If you are in that situation, there are a few steps to take which will help you store your grain long-term in good condition.

This chart shows storage risks to grain at various temperatures and moisture levels.
Figure 1: Grain stored too warm and/or wet is susceptible to pests and diseases (click image for larger version). Image adapted from United Grain Growers, Winnipeg MB.


When it comes to storage, keep grain cool and dry to prevent spoilage.  Diseases, moulds and insects thrive in warm and wet conditions (Figure 1).  For long term storage (longer than 6 months), dry the grain an additional 1-2 points below “normal” storage moisture, to provide additional protection against spoilage (see Table 1).

Table 1. Recommended moisture levels for short- and long-term storage of corn, soybeans and wheat.
Grain Recommended moisture for short-term storage (less than 6 months) Recommended moisture for long-term storage (greater than 6 months)
Corn 15.5% 13%
Soybeans 13% 11%
Wheat 14% 13%

If grain is slightly wetter than desired, an aeration fan can be used effectively for small amounts of drying.  A commercial grain dryer may not be practical or efficient to remove a small amount of moisture.  Drying depends on the outdoor air conditions.  Using the Equilibrium Moisture Content (EMC) chart for the correct grain (see table 2 for Corn), look up the outdoor temperature and humidity, and find the corresponding grain moisture level.  You can also use BINcast, which is an online tool.

Table 2: Equilibrium Moisture Content of corn at various air temperatures and humidity levels
Air Temp (deg. C) EMC (% wet basis) at Relative Humidity (%)
50% 60% 70% 80% 90%
0 13.7 15.1 16.6 18.4 21.3
5 13.1 14.4 15.9 17.8 20.7
10 12.5 13.8 15.4 17.3 20.2
15 11.9 13.3 14.9 16.8 19.8
20 11.5 12.8 14.4 16.4 19.4
25 11.0 12.4 14.0 16.0 19.0
This image shows a weather forecast and equilibrium moisture content prediction from BinCast
Figure 2: BINcast provides an hourly forecast of temperature and humidity at your location, and predicts the Equilibrium Moisture Content of a chosen grain type (in this case, corn).  Image source: BINcast®

BINcast provides a 5-day hourly weather forecast (temperature and humidity) as well as a predicted Equilibrium Moisture Content for your grain.  To use BINcast, register for a free account at, then choose “BINcast” from the menu.  Find your location on the map, and a weather forecast & predicted moisture content will be generated for your chosen grain type (Figure 2).  This is a great way to plan ahead, as you can see the full week’s forecast to know if weather conditions will be suitable for drying.

Run the fan whenever the moisture level in the EMC chart or on BINcast is below the actual moisture of the grain.  As a rule of thumb, relative humidity below 65-70% humidity usually provides good drying conditions.  Turn the fans off whenever the humidity climbs, to avoid adding moisture back into the grain.  Eventually, the grain will dry down, although this can take several weeks.  If the aeration fan is very small, move the grain to a bin with a larger fan to speed up the drying process.


Aeration accomplishes 3 goals:

  • maintain grain temperatures for long-term storage
  • equalize moisture throughout the bin
  • prevent convective air movement within the bin.

In the spring, as the weather warms up and the sun shines on the side of a grain bin, the metal wall will heat up.  This heat will transfer to the grain near the wall, but the grain in the centre of the bin will still be cold from winter storage.  The warm grain heats the air around it, which beings to rise and picks up moisture from the grain.  The warm air begins to cool once it reaches the attic space, and falls through the centre of the bin, and its moisture condenses on the cold grain.  A high-moisture area eventually forms at the bottom centre of the bin.  This area is out of reach of monitoring, and will create problems when unloading the bin.  (Figure 3)

This diagram shows convective air movement inside a grain bin
Figure 3: warm spring sunshine on a bin filled with cold grain can create unrestrained air movement, causing a high-moisture pocket to form at the bottom of the bin (click image for larger version)

To reduce convective air movement, maintain the grain temperature within 5-10 degrees C of the average weekly outdoor air temperature, by running the aeration fan regularly.  During very warm months, try to keep grain temperatures below 10 degrees C if possible – in general, the risk of spoilage from convective air movement is lower than risk of spoilage from higher temperatures.  Even through the summer, average daily low temperatures in the low-to-mid-teens are common, making night-time aeration a good option.


If your bins have temperature and moisture monitoring cables, check them frequently. Many modern systems can send alerts to your computer or mobile device, if temperatures or moistures begin to increase.

Physically check your bins once a week, once daytime temperatures exceed 10-15 degrees C.  Climb each bin, open the hatch and look visually for signs of spoilage.  Are there indications of insects/mould?  Is the grain bright, or is it dusty/dull?  How does the grain smell?  Your nose can quickly tell you what your eyes might miss.

If there are any signs of spoilage, move the grain out of the bin as quickly as possible. Monitor the grain as it is being unloaded.  If the spoilage is contained to one area of the bin, you may be able to separate most of the “clean” grain.


With a bit of planning and careful management, high-quality grain can safely be stored into summer and beyond.  Aeration is the primary tool to keep grain dry and in good condition.

For more information:

OMAFRA Factsheet on Grain Aeration (

Storing Wet Corn Safely (

Natural Air Drying of Corn (

How to dry soybeans in a bin (

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