Moisture content is reported on all official grade certificates, and maximum moisture is usually specified in the contract by the buyer. However, moisture is not a grade factor, so it does not influence which numerical grade will be assigned to the sample. Moisture content is important because it affects the amount of dry matter being sold and purchased. In addition, the average moisture content and its variability in a shipment of corn affects the quality of that shipment at destination. To maintain good quality, recommendations for clean corn are as follows: 14% maximum moisture content under aerated storage in U.S. corn-belt conditions for storage no more than six to twelve months, and 13% or less moisture content for storage of more than one year.
Corn is typically transported in railcars or in closed, nearly airtight holds during ocean voyages. Few bulk carriers or railcars have the ability to aerate the grain mass during transit. This lack of aeration can create an ideal environment for pockets of high-moisture grain to initiate microbiological activity. In addition, temperature variations in the grain mass can cause moisture migration, resulting in warm, moist air condensing on colder surfaces of grain, near sidewalls or on the underside of hatch covers, which can lead to the development of spoilage or hot spots. Hot spots are small pockets of grain where the temperature and moisture content become abnormally higher than the average for the cargo. Thus, uniformity of moisture content among sublots and average moisture values of 14% or below are important for minimizing the risk of hot spots developing during transit.
- Average U.S. Aggregate moisture content (14.4%) was slightly higher than 2016/2017 (14.3%), and the same as 2015/2016 and 5YA (both 14.4%).
- Moisture content variability among samples for 2017/2018 (standard deviation of 0.29%) was slightly lower than 2016/2017 (0.34%), 2015/2016 (0.32%) and 5YA (0.35%).
- Moisture content of the samples ranged from 13.1% to 15.3%, or 2.2 percentage points. This is the same range as 2016/2017 but less than the 2015/2016 range (2.7 percentage points).
- Of the 2017/2018 samples, 31.2% had moisture content above 14.5%, which was higher than the 24% in 2016/2017 and 26% in 2015/2016.
- Average moisture content decreased between harvest (16.6%) and export (14.4%) and uniformity among samples increased, as indicated by the lower standard deviation at export (0.29%) compared with harvest (1.90%). Drying at the local elevator lowers harvest moisture content to levels safe for storage and transport. Uniformity in moisture content increases between harvest and export as the corn from various sources is commingled and conditioned to bring it to the desired moisture content.
- The Pacific Northwest ECA average moisture content (14.2%) was lower than the Gulf (14.5%) and Southern Rail (14.3%) ECAs. The Pacific Northwest ECA also reported the lowest average moisture content among the three ECAs for 2016/2017, 2015/2016 and 5YA.
- Average moisture was slightly lower for contracts loaded as U.S. No. 2 o/b (14.4%) than for contracts loaded as U.S. No. 3 o/b (14.6%). The moisture range for U.S. No. 2 o/b (13.5 to 15.3%) was narrower than the range for contracts loaded as U.S. No. 3 o/b (13.1 to 15.3%). The moisture standard deviation for contracts loaded as U.S. No. 2 o/b (0.25%) was lower than for contracts loaded as U.S. No. 3 o/b (0.35%).
 MWPS-13. 1988. Grain drying, handling and storage handbook. Midwest Plan Service No. 13. Iowa State University, Ames, IA 50011.