While there has been much awareness and research on the use and value of distillers’ dried grains with solubles in swine diets, more is needed on product quality and handling. Nutrient variability is a primary concern, especially with DDGS' rapidly growing supply. From a nutritionist’s or pork producer’s point of view, controlling product variability is outside of his influence. Essentially you get what ethanol plants produce, and, at best, controlling the supply depends on how well you know and select the supplier. But this doesn’t mean that variability can’t be controlled in the production process. Our research group has quantified factors that affect DDGS’ physical and nutrient variability during drying. While the notion that the addition of variable condensed distillers’ solubles or CDS — also known as syrup — caused the nutrient composition variability, the Purdue University study quantified the effects on nutrient composition. The study showed that while the crude-protein content increased, the fat and ash content decreased as the syrup level decreased from what the plant normally added (Batch 1) to zero (Batch 3).
The amino acids (methionine, lysine, threonine and tryptophan) also increased significantly as the syrup level decreased. So DDGS variability is largely caused by varying syrup levels during drying, which is not standardized at U.S. ethanol plants. Even within a plant, variability occurs depending on how well solid (wet distillers’ grains) and liquid (syrup) co-product streams are managed during production.
In another related study at Purdue, a model was developed that can correlate nutrient composition to syrup levels in DDGS, thereby providing a mechanism for ethanol plants to control variability during manufacturing. This insight provides opportunity for buyers and sellers to work with ethanol plants so that the DDGS produced could be designed for swine or other livestock rations. The impending growth in the DDGS supply is forecast to increase to 40 million tons annually by 2015. This means addressing and controlling DDGS quality will be increasingly important to expanding its use. Producing DDGS for targeted end-use might become more attractive in the near future.
Another issue that needs to be highlighted is how the chemical composition affects product flow and storage. DDGS’ chemical composition was shown to affect its ability to absorb moisture from the air. A 2009 Purdue study showed that the final moisture which DDGS will equilibrate to when stored between 50° F to 104° F in 65 percent relative humidity (conducive to the growth of storage fungi) was 2 percentage points less for DDGS with half the amount of syrup level. Less moisture from atmospheric air at high humidity is absorbed by DDGS with a low syrup level than DDGS with a high syrup level. This has implication to product caking in feed bins on the farm, storage bins at warehouses and during transport, where poor unloading has been reported industry-wide.
So what can be done? First, DDGS is a hygroscopic product — its hygroscopic behavior will change with its chemistry. Relating chemistry to sorption behavior will help guide DDGS sellers and buyers in the handling challenges, especially if it’s moving to a warmer, tropical climate. Practical management tools still being developed from the research will hopefully provide much-needed solutions to the industry.
Another aspect is particle segregation and its influence on DDGS sampling error and mixing in feed rations. In processing corn into ethanol, kernels are ground, cooked and fermented. The unfermentable residue of corn, known as dry grind, is the fractionated parts of the corn kernels (fiber, germ, protein and particle agglomerates). Particles making bulk DDGS will tend to segregate during handling, especially with large-particle-size distribution. Syrup levels play a role, as the particle-size spread increases as the syrup level increases.
Purdue research reported that one potential cause of nutrient variability may be particle segregation during handling. This is primarily caused by particle-size differences and, to a lesser extent, by density variations. Particles with similar characteristics, such as size and/or density, tend to collect in the same region. When DDGS is piled or filled in a bin, the fines concentrate in a pile’s center, while larger particles concentrate at the periphery. Ensuring that feed ingredients are appropriately mixed will help mitigate this problem. Also, using appropriate protocols to sample DDGS from representative areas in the bulk ensures that you get accurate data.
Lastly, it would be good for both buyers and sellers to discuss sampling protocols and test methods rather than assuming everyone knows what he should be doing.