Grain Storage - Aeration Part I

Aeration is a vital topic for anyone involved in grain storage. Maintaining grain

inventories is a top priority in the industry, and an effective grain aeration system is

crucial to achieving that goal. With years of personal experience in this field, I initially

thought authoring this article would be straightforward. However, to ensure I provided

accurate information, I researched various technical articles on aeration.

Effective grain storage is vital for maintaining the quality, safety, and marketability of

stored grains such as corn, wheat, and soybeans. One of the key components of

successful grain storage management is aeration – the process of controlling the

temperature and equalizing the moisture content of the grain mass. This paper aims to

provide an overview of grain aeration management, focusing on various designs,

techniques, and technologies. Procedural topics such coring and monitoring of the

grain will also be reviewed.

Aeration must be approached systematically to optimize grain preservation and reduce losses due to spoilage.

A Brief History of Grain Aeration

Historically, tests of grain aeration to cool and dry combine-harvested wheat by F L.

Fenton, C. O. Swanson, and Orval C. French at Kansas State University in 1930-31

showed mechanical ventilation to be more effective than natural draft ventilation.

Mechanical aeration was further developed in the 1940's post-World War II era as grain

surpluses increased and larger storage facilities came into use. Studies in 1944-45 by USDA

agricultural engineers G. W. French and W. V. Hukill cooperating with Iowa State

University proved that mechanical aeration prevented moisture migration. G. H. foster

and R. N. Robinson, USDA agricultural engineers cooperating with Purdue University,

demonstrated the effectiveness of aeration in a large horizontal grain storage in 1949-

50. The first successful grain aeration system for large vertical grain silos was designed

by agricultural engineer Meryl Todd for the Producers Rice Mill in Stuttgart. Eli Troyer,

Edon, Ohio, was one of the early inventors of automatic aeration controllers for grain bins.

While the justification, benefits, and rationale for aeration are largely consistent,

opinions on the best approaches vary significantly. Key issues, such as positive versus

negative airflow, desired airflow rates (cfm/bushel), fan types, duct floor patterns,

optimal times to run aeration systems, and more, often lack a clear consensus.

Additionally, several variables influence decision-making, including commodity type, grain quality, storage type (on-farm or commercial), cooling versus drying needs,

geographic location, ambient conditions of temperature and humidity ranges, and

expected storage durations.

This post will focus on aeration from the perspective of a commercial grain elevator

located in the U.S. grain belt, primarily handling beans, corn, and wheat. Due to the

numerous variables and perspectives on this topic, this article will be divided into two

parts. Part I will cover the common reasons for aeration, its benefits, and basic

concepts, while Part II will delve into diverse opinions on how and when to use aeration

effectively.

Understanding Aeration

Simply put, aeration of stored grains involves forcing small volumes of air through the

grain mass to cool it and maintain its quality by reducing temperature and, to a lesser

extent, moisture. Aeration systems use fans to move air either from the bottom

(pressure airflow) or from the top (suction airflow). This air is conveyed through a

network of ducts strategically placed to ensure even distribution throughout the grain

mass. By circulating cool air, aeration lowers grain temperatures to levels that allow for

safe extended storage with minimal quality loss.

In addition to cooling, the grain aeration helps to equalize moisture throughout the grain

mass, helping to minimize moisture migration which can lead to mold and insect

infestations. The cooler uniform temperatures will reduce the deterioration rate of the

grains and once sufficient cooling has occurred reduce or cease insect activity. Aeration

may also provide a benefit in removing stale or musty odors from the grain. From a

safety perspective, well-managed stored grains should remain free-flowing and

shouldn’t require mechanical or manual intervention to empty the bin until the angle of

repose is reached.

Iowa State University - Integrated Crop Management

Benefits of Aeration

• Reduces hot spots, maintaining a consistent equalized temperature, which inhibits mold growth.

• Extracts moisture to reduce condensation and ambient.

• Deters insect activity by maintaining environments less favorable for pests.

• Preserves the nutritional and physical quality of the grain.

Grain - Type and Quality

The required air for an efficient aeration system varies depending on the type of grain in

storage and on the quality of the stored grain . In grain storage, corn and soybeans generally require similar aeration needs ,wheat requiring less. Regardless of the grain type it is always a good idea to run some air through the grain when stored to remove “harvest heat” or heat from any grain that has been dried.

In my experience, among the three major grains in the U.S., wheat is the easiest to

store, followed by soybeans and then corn. Wheat has lower moisture and oil content

than soybeans and corn which improves its storability. Wheat requires less aeration

than corn and soybeans because it has lower airflow resistance. I have stored wheat in

a northern climate in upright concrete storage for over eight years in the past,

supplemented by scheduled turning of the bins and fumigations.

While soybeans have higher oil content than corn (18-22% vs. 5%) in the U.S. they are

generally delivered into the elevator at harvest with moisture levels around 12% or less, where corn may be delivered in the 15.0 to 22.% range. My experience has also been larger volumes of corn are generally carried longer into the spring and summer than soybeans. The lower moisture and typically shortened duration of storage time tends to aid storability. Soybeans also have about 25% less airflow resistance than corn, allowing for more effective use of aeration.

Part II will address the recommended airflow rates, but it's important to remember thateach grain type necessitates different aeration strategies depending on its unique characteristics.

Storage - Design

As discussed in the blog on storage there are diverse types, upright concrete,

corrugated steel, sheds, and/or flat buildings. There is temporary storage with walled

piles and bunkers or grain just piled on the ground. There are advantages to each but

when looking at storability a couple of issues come to the forefront, insulation, and static

pressures.

Upright concrete bins typically are in the 100’ to 130’ height, some even taller. This

increases the amount of static pressure created in a bin during aeration . In the context

of grain aeration, static pressure refers to the resistance to airflow through the grain

mass, measured in inches of water column (in. H2O), that the aeration fan needs to

overcome to move air through the grain. Conversely the lower heights seen in traditional

corrugated bins reduce the amount of static pressure. With that being said a lot of the

newer corrugated bins are now approaching the 100’ height with the tallest bin being at

112’. Bin diameter also plays a part in the effectiveness of aeration with large diameter

bins offering a greater challenge to achieve equilibrium with the airflows. Diameters of

up to 156’ are now available in corrugated bins where typically concrete bins are found

in 30, 40, or 50. Diameters.

Upright concrete bins provide a good level of insulation that typically will hold cooler

grain temperature into the spring and summer than corrugated steel bins. With their

increased diameters steel bins have larger roof surface and typically more wall

exposure to direct sunlight than a similar sized storage facility with concrete bins. This

direct exposure to sunlight on steel can create heating, and one side of the bin typically

will have more exposure than the other creating temperature and moisture equilibrium

issues.

Geography - Latitude, Altitude, and Climate

The location of grain storage plays a significant role in the design of the aeration system

and the practices utilized to maintain grain quality. Generally, it is easier to store grain in

the cooler, higher latitudes of North America than in the warmer, more humid southern

regions. The same principle applies globally: cooler climates found closer to the poles

typically favor grain storage. Higher altitudes also experience cooler temperatures along the same longitudes. Warmer conditions often lead to higher humidity levels, which can negatively impact grain storage.

It is important to distinguish between weather and climate. Weather is the short-term,

day-to-day atmospheric conditions, while climate is the long-term, average weather

patterns in a specific area, typically over 30 years or more. When designing aeration

systems, it is necessary to take climate into consideration. When operating an aeration

system, it is important to take weather into consideration.

Cooling vs. Drying

While we’ve defined the primary purpose of aeration as cooling grains during harvest or

drying to improve storability, advancements in aeration system design have made it

possible to go beyond merely cooling to actively drying. Enhanced aeration systems can

effectively remove higher levels of moisture content from the grain than traditional

cooling systems. This capability is crucial for maintaining grain quality and preventing

spoilage, especially in regions with humid climates.

The next installment, Part II, will explore various concepts and operational activities

related to aeration, focusing on how and when to implement these systems effectively.

This will include discussions on airflow rates, strategies for cooling versus drying, and

best practices based on specific grain types and storage conditions.

We welcome your comments on this post, as well as requests for additional topics to be

covered in future articles. Please feel free to reach out with questions or suggest

subjects that interest you.

Regards,

Grain Guy Fifty