Until recently, the primary objective of the bioethanol industry was ethanol production. That was before a little bitty virus caused a very big disruption in just about everything, including the amount of gasoline that is no longer being consumed.
Today, however, some distillers are placing more emphasis on livestock feeds as they transition to offering a range of new products in addition to continued production of dried distiller grain with solubles (DDGS). DDGS is a co-product with ethanol and is fed to cattle, swine and poultry. Cattle account for nearly 80% of DDGS consumption within the United States with 50% of the amount fed to beef cattle and 30% to dairy cattle.
New advancements in separation and fractionation of corn kernel components within the ethanol manufacturing process allow development of functional protein products to fill specific animal nutrition needs. These new products have supplementary benefits in addition to the protein value.
The new opportunities are better understood after a review of the traditional ethanol fuel refining process. There are two primary methods of producing ethanol from corn—dry milling and wet milling. Approximately 90% of the corn ethanol produced in the United States is by dry milling.
“For wet milling, corn is mechanically separated into starch, fiber, corn germ and protein by soaking in sulfurous acid solution for two days. The starch is separated from the mixture and used to produce ethanol, corn syrup or food grade starch,” said Caroline Clifford, senior research associate, The Pennsylvania State University. “Wet milling also produces feed, corn oil, gluten meal and gluten feed.”
Dry milling is a simpler process than wet milling, but it has traditionally produced fewer products. These have been primarily ethanol, carbon dioxide, DDGS and non-food corn oil. The first step in dry milling is grinding corn, typically in a hammermill. After the corn is ground, it is mixed with heated water to form a mash or slurry. The slurry then goes through cooking, liquefaction and saccharification stages. Liquefaction breaks up the longer starch chains into smaller chains and saccharification hydrolyses the starch into sugar. Enzymes and yeast are added during these latter two stages.
“Next stage in the process is fermentation where yeast is generated and carbon dioxide is produced,” says Clifford. “After fermentation, the slurry is distilled to make ethanol. The remaining slurry is centrifuged, producing distiller grain and the remaining substance from that process is evaporated to create distiller solubles. Mixing the distiller grain with the solubles produces DDGS.”
The new process
“The new corn separation technologies are currently being used in some dry-grind fuel ethanol refineries,” said Sarah McKay, director of market development, National Corn Growers Association. “These technologies allow more precise isolation of corn components through additional mechanical separation steps.”
The additional steps provide more control points which provide opportunity to produce more consistent products and optimize animal feed quality, she says. “In addition, it is possible to recover side streams for specific nutritional purposes. Reduced dryer loading in the new processes improves nutritional value of DDGS and decreases plant carbon usage. This is likely to also improve sustainability for the entire system.”
One commercially available process, Still Pro 50, which has been on the market in limited amounts for 10 years, is now available in significantly greater quantities, says Peter Williams, senior nutritionist for Fluid Quip Technologies. “Compared to DDGS, Still Pro50 is a very different product and has a much higher nutritional value. Still Pro50 contains approximately 93% dry matter, 49% crude protein, 88% TDN (total digestible nutrients), 4% fat and 25% spent yeast from fermentation. In comparison, DDGS contains 6% yeast.”
Research has shown yeast to improve ruminant digestion. That’s because yeast cultures encourage growth of beneficial bacteria which break down plant cellulose in the rumen. These bacteria are critical for healthy digestion of feed. Also, yeast cultures mop up oxygen in the cow’s rumen. This action is important because fermentation is a necessary process in forage digestion by cattle and it only occurs in the absence of oxygen.
Fears is a freelance writer based in Georgetown, Texas.