Corn Quality

By Charles Hurburgh | November 15, 2010
Anyone who thought corn quality was automatically assured has had some learning experiences in the past 12 to 18 months. Let's look at some of those and their meaning for future years.

Corn in 2009 was extremely wet and had low test weights (often 52 pounds per bushel and less) that did not increase significantly after drying. The situation was caused by a wet, cold growing season followed by a cloudy, humid fall, with just enough heat to put field molds in optimal growing conditions. This was the source of higher-than-normal damaged kernel levels out of the field, with progressively higher risk of vomitoxin, zearalenone and fumonisin from west to east in the Corn Belt. Mycotoxins do not go away in storage and will show up in carryover 2009 corn. Storage molds do not normally produce toxins to the extent that field molds do, but experience is limited in extreme high-damage cases. On the plus side, tests showed that higher moisture and lower test weight by themselves did not inherently reduce ethanol yield on a dry weight basis.

Low test weight corn does not store well; 2009 corn had about 50 percent of the normally expected shelf life. In the fall we had very aggressive storage molds that created distinctly bad corn, especially when put in bunkers. This summer, the same storability problem contributed to a rapid increase in less aggressive, but still problematic blue-eye mold (germ damage). With much of the Corn Belt getting 150 to 200 percent of normal rainfall in summer 2010, even low moisture corn was at risk, and the air conditions were such that air movement through grain did little good. Blue-eye does not create heating, just spoiled grain.

In 2010, conditions were better, but not as good as originally hoped. Excessive rainfall and warm nights reduced corn yields. Quality is good but not excellent; expect 54 to 56 pound test weights, but little field damage. The warm, dry fall nearly eliminated artificial drying with most corn coming out of the field less than 17 percent moisture, and some below 14 percent. No drying means fewer broken kernels and improved storage life. The 2009 carryover corn, however, will be blended over time to the extent that standards, as enforced by plant grading practices, will allow. Even if you grade accurately and consistently, expect damage at, or near, contract specs. There will be risk in not grading inbound corn well. Damage (mold) has potential to create fermentation problems that need increasingly controversial rescue antibiotic treatments.

Important corn quality factors, and their effects include:
Composition: Ethanol yield can be estimated fairly accurately (0.04 gallons per bushel) by calculation from protein, oil and density measured with a near infrared analyzer. Protein and oil also affect distillers grains quality.

Damage: Mold interferes with fermentation; although published quantitative data is scarce. A good inbound grading program would allow individual plants to make measurements. Fermentation problems cause distillers grains variability as well as lost ethanol.

Mycotoxins: Mycotoxins go directly into distillers grains with a multiplier of three, becoming a feed safety issue.

Do not assume inbound corn will on average have adequate quality. Individual fermenter batches will not always receive "average" corn, it may be the last 10-20 trucks run straight down through the bin. In a future article I will discuss some specific operational and data management strategies to improve grain grading without restricting receiving. As a starting point, focus on the factors that matter, use periodic composites (say a combination of 25 trucks) to establish a moving average; carefully grade those individual lots that look to be at or above specification, and, for mycotoxins, examine the individual sellers that contribute to a high composite. Many corn processors have found that professional third party inspection is cost effective.

High yields and smooth fermentations begin with quality raw materials; accurate grading with effective data management are preventive operations that can buffer the impact of increasingly variable corn quality. Climate experts predict continued weather extremes.

Author: Charles R. Hurburgh, Jr.
Professor in Charge, Iowa Grain Quality Initiative
Iowa State University
(515) 294-8629
tatry@iastate.edu