Understanding Corn Shrink
Shrink is the loss of weight caused by drying and handling the grain and is expressed as a percentage of the original quantity. It is a loss of revenue associated with mechanically drying corn.
"Corn buyers account for shrink by discounting the price per bushel that they offer (i.e. a charge per bushel) or by calculating the reduction in bushels. When producers are considering whether to sell corn at harvest or store on-farm, all costs, including shrink, must be evaluated," explained Kim Dillivan, SDSU Extension Crops Business Management Field Specialist.
Moisture Shrink
When corn is dried, Dillivan said the largest component of weight loss is the removal of moisture. "This loss of mass is called moisture shrink and is calculated by multiplying a moisture shrink factor by the percentage of water removed," he said.
The moisture shrink factor is the percent weight loss per percent moisture removed and is equal to: 100/(100 - final moisture %).
For example, corn dried to 15% moisture has a shrink factor of 1.176 (100/85). Moisture shrink factors are independent of the initial corn moisture percentage. Moisture shrink factors are dependent on final moisture percentage and several are shown in Table 1.
"The moisture shrink factor is a constant for each final moisture level achieved. For example, the moisture shrink (weight loss) is 1.176 percent for each point of moisture removed when the final moisture content of the corn is 15 percent (Table 1)," Dillivan said.
As Dillivan mentioned earlier, moisture shrink or percent weight loss equals the percentage of moisture removed multiplied by the moisture shrink factor.
He shares an example: corn dried from 25 to 15.5 percent moisture (loss of 9.5 percentage points of water) has a loss of mass equal to 11.23 percent (9.5 x 1.183). In this example, the percentage reduction from the original weight (11.23 percent) represents the amount of water removed when drying 25 percent moisture corn to 15.5 percent.
Handling Loss
Although the majority of weight lost when drying corn is a consequence of water removal, some dry matter is also lost, explained Dillivan. "Called handling loss and sometimes called invisible shrink, this small reduction in mass results from broken kernels, foreign material, loss of oil or other compounds, and continued respiration of the seed kernels," he said. "However, handling losses are usually quite small relative to water loss."
The amount of handling loss depends on several factors, including;
- Physical quality of the corn
- Method used to dry the corn
- Dry time
- How the corn is handled during drying
According to research conducted at Iowa State University, the estimated on-farm handling losses ranging from 0.22 to 1.71 percent; and losses from commercial drying systems ranged from 0.64 to 1.33 percent. The Iowa State University researchers found the 3-year, on-farm handling loss average was 0.82 percent compared to 0.88 percent for the commercial facilities.
Calculating Total Shrink
Grain buyers will account for both moisture shrink and handling loss. This is called total shrink and to calculate buyers will often use either drying tables or a constant shrink factor. Grain drying tables include a water shrink loss which is calculated by using shrink factors from Table 1, plus a loss from handling explained Dillivan.
Dillivan said that often this handling loss is assumed to be 0.5 percent.
Another method used to calculate shrink is to use a constant shrink factor; often 1.3, 1.4, or 1.5 per percentage point of moisture removed. "A constant shrink factor is used to account for both water and handling losses," he said.
Total shrink (percent total weight loss) is found by multiplying the percentage moisture removed by the constant shrink factor.
For example, assuming a constant shrink factor of 1.4, corn dried from 25 to 14.5% moisture (loss of 10.5 percentage points of water) has an assumed loss of mass equal to 14.7% (10.5 x 1.4). In this example, the estimated water loss equals 12.27% (10.5 x 1.169). Therefore the grain buyer is assuming a handling loss of 2.43% (14.7 - 12.27).
The handling loss assumed increases as the constant shrink factor is increased. Table 2 provides handling loss values for various constant shrink factors based on 15% final corn moisture. The handling loss is found by subtracting the water shrink from the total shrink.
"Corn shrink occurs whether the grain is stored on-farm or at a commercial facility. Shrink is a reduction of grain weight /mass and results when corn is dried to a moisture content that is safe for storage," Dillivan said. "When corn buyers apply a constant shrink factor to estimate shrink (e.g. 1.4), they are accounting for moisture and handling losses."
Producers can use Table 2 to find the handling losses assumed by buyers when they apply a constant shrink factor to purchases of corn dried to 15%.
Table 1. Moisture Shrink Factors for Final Moisture Levels.
(per moisture point removed) | |
Table 2. Handling Loss for Various Constant Shrink Factors for 15% Moisture Corn.
Content % | |||||
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