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September 2017
URL: http://www.kingcorn.org/news/timeless/WaterShrink.html

Converting Wet Corn Weight to Dry Corn Weight

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen at purdue.edu
Twitter: @PurdueCornGuy

 

Corn is often harvested at grain moisture contents higher than what is desired by grain buyers, which is typically about 15% moisture. Wetter grain obviously weighs more than drier grain and so grain buyers will "shrink" the weight of "wet" grain to the equivalent weight of "dry" grain and then divide that weight by 56 to calculate the market bushels of grain they will purchase from the grower. The two sources of weight loss due to mechanical drying are 1) that due to the loss of grain moisture itself and 2) the anticipated weight loss due to dry matter loss during the grain drying and handling processes (e.g., broken kernels, fines, foreign materials).

An exact value for the handling loss, sometimes called "invisible shrink", is difficult to predict and can vary significantly from one grain buyer to another. For a lengthier discussion on grain weight shrinkage due to mechanical drying, see Hicks & Cloud, 1991.

The simple weight loss due to the reduction in grain moisture represents the greatest percentage of the total grain weight shrinkage due to drying and is easily calculated using a handheld calculator or a smartphone calculator app. In general terms, you first convert the "wet" weight to absolute dry weight. Then you convert the absolute dry weight to market-standard "dry" weight at 15% grain moisture.

For example, if the initial grain moisture content is 20%, then the initial percent dry matter content is 80% (e.g., 100% - 20%). NOTE: The initial percent dry matter content varies depending on the initial grain moisture content.

If the desired ending grain moisture content is 15% (the typical market standard), then the desired ending percent dry matter content is 85% (100% - 15%).

Multiply the weight of the "wet" grain by the initial percent dry matter content, then divide the result by the desired ending percent dry matter content.

Example:

  1. 100000 lbs of grain at 20% moisture = 80000 lbs of absolute dry matter (i.e., 100000 x 0.80).
  2. 80000 lbs of absolute dry matter = 94118 lbs of grain at 15% moisture (i.e., 80000 / 0.85).
  3. 94118 lbs of grain at 15% moisture = 1681 bu of grain at 15% moisture (i.e., 94118 / 56).

One take-home reminder from this little exercise is the fact that the grain trade allows you to sell water in the form of grain moisture... up to a maximum market-standard 15% grain moisture content (or 14% for long term storage). Take advantage of this and maximize your "saleable" grain weight by avoiding delivering corn grain to the elevator at moisture levels less than 15% moisture content.

Related reading

Hicks, D.R. and H.A. Cloud. 1991. Calculating Grain Weight Shrinkage in Corn Due to Mechanical Drying. National Corn Handbook Publication NCH-61. https://www.extension.purdue.edu/extmedia/nch/nch-61.html [URL accessed Sep 2017]

Nielsen, RL (Bob). 2014. Corn Grain Test Weight. Corny News Network, Purdue Extension. http://www.kingcorn.org/news/timeless/TestWeight.html [URL accessed Sep 2017]

Pryor, Randy, Paul Jasa, & Jenny Rees. 2017. Plan Harvest to Deliver Soybeans at the Optimum Moisture. Cropwatch, Univ Nebraska Extension. http://cropwatch.unl.edu/2017/plan-harvest-deliver-soybean-optimum-moisture [URL accessed Sep 2017]