How to Determine Corn Moisture Shrink and Total Shrink

Field Facts written by Curt Hoffbeck, DuPont Pioneer Area Agronomist

Moisture Shrink

The weight reduction as grain is dried is referred to as "moisture shrink." Moisture shrink can be determined by multiplying a moisture shrink factor by the change in moisture. The moisture shrink factor is determined by the following equation:

Moisture shrink factor = 100 divided by (100 minus percent final moisture)

This factor represents the shrink that occurs for each percentage point of moisture removed from initial to final moisture. Moisture shrink factors based on final moisture content are shown in Table 1.

Table 1. Moisture shrink factors for drying shelled corn to various moisture levels.

 Moisture shrink factors for drying shelled corn to various moisture levels.
 

For instance, the shrink factor when drying corn to 15.5% moisture is 1.1834. Therefore, the moisture shrink when drying corn from 25.5% to 15.5% is 10 X 1.1834 = 11.83% (11.83% loss in grain weight due to the water removed during the drying of 25.5% moisture corn to 15.5% moisture.)

Example moisture shrink calculations: Assume we have 1,000 lb of 25.5% moisture corn, and we want to know how many bushels we would have at 15.5% final moisture:

wet bushels = 1,000 lb ÷ 56 lb/bu = 17.9 wet bu.

moisture shrink factor = 100 ÷ (100 - 15.5) = 100 ÷ 84.5 = 1.183% per point

moisture shrink = (25.5 - 15.5) x 1.183% per point = 10.0 points x 1.183% per point = 11.83%

standard bushels = 17.9 x [(100 - 11.83) ÷ 100] = 17.9 x 0.8817 = 15.8 std bu.

Grain dryer

Figure 1. Reduction of grain mass due to drying and handling losses is referred to as "shrink."

 

Handling Loss

Note that shrink that is assessed when grain is marketed will likely be higher than the moisture shrink to include some facility operation costs and handling losses. Although most of the weight loss during drying is water, a small portion is dry matter. This loss is often called "invisible shrink," but may be better described as "handling loss." Some of the handling loss is due to loss of volatile compounds such as oils, mechanical losses from broken kernels and foreign material, and possibly also due to respiration of the seed itself. Handling loss will normally be far less than that due to water.

The actual amount of handling loss will depend on the initial physical quality of the corn, the method of drying, and the handling processes during drying. Research at Iowa State University determined that on-farm handling losses ranged from 0.22% to 1.71%. Losses from commercial drying systems ranged from 0.64% to 1.33%. The 3-year on-farm average was 0.82% compared to 0.88% for the commercial facilities.

 

Calculating Total Shrink

Shrink factors used by grain buyers account for both moisture shrink and handling loss. Grain buyers typically use drying tables or a constant shrink factor to "pencil shrink" the grain they buy.

Some grain buyers use drying tables which include moisture shrink and a constant handling loss, usually 0.5% of the initial weight of the grain. Using this method, the formula for calculating total shrink is: Total Shrink = (total moisture shrink) plus (handling loss).

Example: If we were to dry shelled corn from 25.5% to 15.5% moisture (a removal of 10.0 percentage points), the total moisture shrink would be 10.0 multiplied by 1.183 (from Table 1), or 11.83% of the original grain weight. Add to this the 0.5% handling loss for a total shrink of 12.33%. Thus, if 1,000 lb. of 25.5% moisture corn were dried to 15.5% moisture, the total weight loss due to water and dry matter removal would be 123.3 lb. (1,000 multiplied by 0.1233). The resulting weight of the dried grain would equal 876.7 lb. (1,000 minus 123.3) or 15.6 standard bushels (876.7 lbs divided by 56 lbs/bu) using this shrink method.

Corn kernels

Figure 2. The actual amount of handling loss of corn grain will depend on the initial physical quality of the corn, the method of drying, and the handling processes during drying.

 

References

Hicks, D.R. and H.A. Cloud. University of Minnesota, Calculating grain weight shrinkage in corn due to mechanical drying. NCH-61, Purdue University, Cooperative Extension Service, West Lafayette, IN.

 

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.

 
 
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