Ask the Doctor: Three Keys to Successful Grain Storage

Before the harvest begins, you need to know the safe storage moisture content of the hybrids you're growing. Once the grains are harvested, it's important to know the relative humidity of the grain and the moisture content.

1. First, monitor the relative humidity or moisture content of the grain.

For example, when a corn hybrid is harvested at 22% moisture content, the relative humidity of that hybrid is typically between 95-100%. At this level, the grain is highly susceptible to spoilage and not suitable for long-term storage. To ensure safe storage, the grain's high moisture content must be reduced until its relative humidity falls below 65%.

2. Second, monitor the grain temperature.

Grain temperature and moisture content are typically monitored using temperature and moisture sensor cables installed within the grain mass. To minimize the risk of condensation and moisture migration, grain temperatures should be maintained within 10°F of the ambient air temperature.

As a general guideline, if the weekly average ambient temperature is approximately 60°F, the grain temperature should be maintained between 50°F and 60°F. This temperature range helps preserve grain quality and reduces the likelihood of spoilage during storage.

3. Third, monitor the fan runtime.

If grain has not been dried to a safe storage condition, typically below 65% relative humidity, or the target storage moisture content, then aeration fans operated as needed to continue drying the grain mass.

In some cases, fan operation may be temporarily turned off to prevent over-drying of the bottom layers of grain. However, fan management should be guided by the system's airflow capacity. For systems designed to deliver less than 0.5 cfm/bu, keeping the fan ON is generally recommended.

However, for systems with airflow rates greater than 1.0 cfm/bu, fans can be turned off during periods of high ambient humidity or unfavorable drying conditions, helping to improve drying efficiency while minimizing the risk of uneven moisture distribution within the bin.

The grain cooling process can take anywhere from 1 to 6 days, depending on airflow rates ranging from 0.1 to 1.0 cfm/bu. With lower airflow rates of 0.1 to 0.2 cfm/bu, the cooling front may take 3 to 6 days to reach the top layer of grain.

The following formula can be used to estimate when the cooling front will reach the top of the grain mass.

As an example, with an airflow rate of 0.2 cfm/bu, the cooling time can be estimated using the formula:

Cooling hours = 15 ÷ 0.2

Therefore, the cooling front would require approximately 75 hours, or just over 3 days, to move through the grain mass and reach the top of the bin.

Higher airflow rates allow the grain cooling process to be completed more quickly. However, the cooling effect is dependent on ambient air conditions. If ambient temperatures increase during the cooling process, the effectiveness of cooling will be reduced.

Usually, the top layer of grain cannot be cooled until the cooling front has first moved through the bottom grain layers.  To successfully cool the upper grain layers, you need both adequate airflow and sufficiently cool ambient air temperatures.

Some farmers reverse the fan airflow and operate the system in suction mode, allowing the upper layers of grain to cool more quickly because cool air is drawn through the top of the grain mass first. However, this approach may result in some warming of the lower grain layers and may not be practical for all storage systems. The operational feasibility and potential impacts on grain quality should be evaluated before implementing this strategy.

Here are some common equipment selection mistakes you can avoid:

1. Selecting the wrong grain depth for natural air drying.

Grain depths greater than 25 feet can significantly reduce the effectiveness of natural-air drying because it becomes difficult to achieve the recommended airflow rate of 1 cfm/bu. For best results, keep grain depth below 25 feet and maintain airflow above 1 cfm/bu.

A common mistake is attempting natural-air drying in a 48-foot-diameter, 10-ring bin with two 20-hp low-speed centrifugal fans, which provides only about 0.6 cfm/bu. Even upgrading to two 40-hp low-speed centrifugal fans may increase airflow to only 0.7 cfm/bu, resulting in substantially higher energy costs with limited improvement in drying performance.

2. Selecting the wrong fan sizing.
   A fan that provides less than 1 cfm/bu of airflow for natural air drying can significantly slow the drying process and reduce drying effectiveness. For example, a system designed to deliver only 0.5 cfm/bu is generally not adequate for effective natural-air drying and may not dry grain quickly enough to maintain grain quality.
   
   
3. Selecting the wrong number of vents.
   For natural-air drying, approximately 1 square foot of vent area is needed for every 1,000 cfm of airflow to prevent condensation and "bin rain" from developing inside.

For example, a 48-foot-diameter, 7-ring bin equipped with two 25-hp centrifugal fans can provide approximately 35,834 cfm of airflow at 1 cfm/bu. At that airflow rate, the bin would require about 36 roof vents with 1 square foot of vent area each, or 24 roof vents with 1.5 square feet of vent area each, to provide adequate exhaust area and minimize condensation issues.