Prevent Problems by Good Corn Grading

By Charles Hurburgh | December 27, 2010
Good corn grading procedures in ethanol plants will continue to be important as 2009 grain is blended into the 2010 crop. The 2009 corn crop started with field molds (normally the source of mycotoxins), continued with aggressive high-moisture-storage fungi and finished last summer with low-moisture blue eye infections. Whether all these types of damage affect fermentation equally is not known. Fermentation problems cause variability in dried distillers grains with solubles (DDGS) as well as lost ethanol. All types of mold discoloration count equally in the total damage (TD) value. TD levels normally never reach the maximum 5 percent level allowed in No.2 corn grades, but we'll likely see high TD this year with carryover 2009 corn being blended into 2010 corn harvested with low moisture and little mold. Blending in truckload lots is difficult, and uniformity is hard to maintain, yet there is a clear incentive to push the limits. Buyers perceived as lax in grading will likely receive higher levels. Also, studies have shown the natural tendency of in-house graders is to progressively underestimate higher TD levels. The other major corn grade factors-test weight, moisture and broken corn/foreign material (BCFM)-have less impact on ethanol production. Tests in 2009 showed low test weight had no significant impact on yield, but was associated with more spoilage in storage. Low test weight corn is often lower in protein, which may increase ethanol yield. BCFM is mainly broken corn. Moisture did not diminish yields on a dry matter basis, though it can create storage problems. Mycotoxins pass through the ethanol process to be concentrated three-fold in DDGS, creating a feed safety issue. In 2009, the cool, wet weather fungi were prevalent and vomitoxin, zearalenone and fumonisin were the mycotoxins found. In hot dry conditions, aflatoxin is more likely. Strip testing is accurate and takes about 10 minutes at a cost of about $10 plus labor. Testing every load is time and cost prohibitive. Test composite samples of inbound corn once or twice per day to spot potential variation in DDGS that would impact buyers. If time-weighted averages show spikes, the individual corn suppliers can be targeted for additional evaluation. Ethanol yield can be estimated to +/- 0.04 gallons per bushel from protein, oil and density measured with a near infrared (NIR) analyzer. Oil content varies much less than protein. Protein is by far the most significant composition factor in corn. For each 1 percent increase in corn protein, ethanol yield drops approximately 0.06 -0.07 gallons per bushel and DDGS protein increases approximately 3 percent on a dry basis. Corn protein varies from 8-10.5 percent and yearly averages can move 0.25-0.5 percent. Uniformity is more important than capturing differences across loads. Protein variation in DDGS of 1-3 percent is more than feed rations account for, but the order of unloading the DDGS barn can help balance the variation. Testing corn composition is best done by a transmission-based NIR unit. These are not the reflectance units useful for testing DDGS, slurry products or fermentation. The fixed cost of a transmission NIR will be about $7,000 to $9,000 per year, plus $1-$2 per sample in operating costs. To upgrade inbound grain evaluation at your plant, move forward in steps rather than making large changes at once: Some thoughts on how to proceed: 1. Have one or two of your employees become well trained. Validate their skills with unannounced comparisons with official grades, in a statistically valid manner. Use them to pass these skills to others through random sample checks. 2. Combine a representative, mechanically divided sample over a day or half day and have your best graders check the composites, including mycotoxin values if there is a concern. Compare to individual load grading. 3. Work with scale house employees to recognize poor corn. Time is best spent on these samples rather than trying to fully grade all. This will also introduce unpredictability in grading frequency, which is helpful in maintaining consistency from sellers. 4. Pull samples just ahead of the hammermill. Record the grade, composition and mycotoxin levels and relate the corn quality measures to individual fermenter performance. Keep time-dated grade records on incoming grain and track its movement through the plant. 5. If you are seeing corn quality impacts and your staff does not have the specialized skills needed, or time to build grading skills, consider third party inspection. Corn evaluation is part of total process control and the collection and analysis of data relating quality to plant performance is critical to continuous improvement. Author: Charles R. Hurburgh, Jr. Professor in Charge, Iowa Grain Quality Initiative Iowa State University (515) 294-8629