Before blending solubles with distillers grains, an ethanol producer can add a preservative to the solubles to inhibit yeast and mold growth, thereby extending the shelf life of wet distillers grains with solubles (WDGS) and modified WDGS for both the ethanol producer and the local feedlot and dairy operations.

WDGS is typically 30 to 35 percent dry matter and MWDGS is typically 42 to 50 percent dry matter. In other words, WDGS can have up to 70 percent moisture content and MWDGS up to 58 percent. Exposed to air, the surfaces of piles of these wet co-products will begin to spoil within three to 14 days, depending on the ambient temperature, according to researchers in the Agricultural Research Division at the University of Nebraska-Lincoln Institute of Agriculture and Natural Resources. The university collaborated with the Nebraska
Corn Board to produce the May 2008 publication "Storage of Wet Corn Co-Products."

Ethanol producers typically use preservatives during summer months, which increases input costs for WDGS. At the same time, demand for WDGS can dip during summer months when feedlots are less active.

"Typically, the number of cattle in feedlots is lower during the summer and so the demand for WDGS is lower. That can lead to lower prices," said Bowe Wingerd, manager of Feedlot Biofuel LLC, a Wichita, Kan., company that has developed a low-volume ethanol plant design for cattle feedlots.

However, diminished summer feedlot activity is not the only factor limiting WDGS purchases for feedlots. The UNL researchers also noted that while ethanol producers might prefer to deliver 25- to 30-ton semi-load quantities of wet co-products to livestock producers, cattle operations with fewer than 1,000 head often find it difficult to use up that much WDGS or MWDGS before spoilage occurs.

Researchers in the Department of Agricultural Economics at Purdue University, who published "Distillers Grain Handbook: A Guide for Indiana Producers to Using DDGS for Animal Feed" in December 2008, point out that if the daily consumption of WDGS per cow is eight pounds, a truckload of the wet co-product would last six days for a herd of 1,000 cows.

Other classes of livestock that consume less would need to be in much larger herds to prevent WDGS spoilage.

Meanwhile, some operations, particularly cow-calf producers, might need to use wet co-products on a seasonal basis.

Seasonal demand for WDGS and MWDGS allows livestock producers to take advantage of lower wet co-products prices. Proper storage techniques can help feedlots to stock up on WDGS and modified WDGS while saving the ethanol producer from having to use more natural gas to dry the product to produce distillers dried grains with solubles.

"Hot summer temperatures cause rapid spoilage of WDGS exposed to air, and so it makes economic sense to have viable storage methods," Wingerd said.

Oxygen is the Enemy
How quickly wet co-products develop noticeable spoilage depends upon heat and humidity. WDGS can spoil in weather above 50 degrees Fahrenheit in just a few days. The key to longer storage is to exclude the oxygen, according to researchers at the Iowa Beef Center at Iowa State University, which serves as the university's extension program to cattle producers. The program publishes the newsletter "Ethanol Feeds: Feeding Distillers Grains to Beef Cattle".

The methods for storing wet co-products are not much different than the methods for ensiling corn silage or high-moisture corn. The UNL researchers said excluding air is key because WDGS are acidic (with a typical pH of 4 to 4.5) and fermentation is unlikely to occur in an anaerobic environment.

The main issue with storage is that it is difficult to pile or compact high-moisture co-products. WDGS tends to flow and spread into wide piles. However, MWDGS does pile adequately and WDG (without solubles) also piles more easily, the UNL researchers said.

Dry forages must be added to WDGS to increase bulk for piling. Mixing forage with WDGS can be difficult because in many cases, the forage will need to be ground first so that it will mix well. According to Pedro Nogueira, a ruminant nutritionist for Kenpal Farm Products Inc. in Centralia, Ontario, one advantage of storing WDGS mixed with forage is that the blend is easier to break during winter months. Kenpal Farm Products published Nogueira's article "Storage of Wet Corn Distillers Grains" in its January 2009 issue of "Dairy Briefs."

Bagging Wet Coproducts
MWDGS can be stored in silo bags under pressure. However, wetter WDGS without added forage stored in silo bags under pressure (300 psi or greater) can result in split bags, which usually occurs within a few days of bagging, according to UNL researchers. Alternatively, WDGS can be stored in silo bags under no pressure, but the method requires more storage area and might result in air pockets within the bags.

The weight of WDGS tends to settle bags to a low height with an expanded width. Because the height of a silo bag is a determining factor for storability, adding forage to WDGS helps to improve bag shape, as noted in "Using Distillers Grains in the U.S. and International Livestock and Poultry Industries," published by the Midwest Agribusiness Trade Research and Information Center at the Center for Agricultural and Rural Development at Iowa State University.

The MATRIC publication says recommended levels of forage for bagging with WDGS are 15 percent grass hay, 22.5 percent alfalfa hay or 12.5 percent wheat straw on a dry matter basis. The corresponding as-is percentages of the mix for the added forages are 6.3, 10.5, and 5.1, respectively. If too much forage is added, the mixture may become too dry and will not compact well inside the bag and some air may become trapped.

WDGS has also been stored in silo bags mixed with DDGS, wet corn gluten feed, soy hulls, corn silage, and beet pulp.

The UNL researchers note that forages will need to be ground before mixing and that higher-fiber forages are the best choices for adding bulk and allow for bagging WDGS under pressure. Therefore, forages such as wheat straw and corn stalks work better than forages that are more digestible.

The Iowa Beef Center notes that MWDGS can be stored in silo bags for 60 to 200 days. The MATRIC publication cites research that says WDGS can be stored in silo bags for six months to a year.

Bunkers
Cattle producers who wish to purchase and store larger quantities of WDGS might have or choose to use bunkers. Once again, the UNL researchers note that while MWDGS appears to pile well in earthen or concrete bunkers, some forage will need to be added to WDGS to increase its bulk so that it can be compacted to exclude air. With either co-product, the bunker should be covered to prevent surface spoilage.

In a bunker, WDGS mixed with 40 percent grass or 29 percent corn stalks on a dry matter basis, for example, allows for adequate compaction and to hold the weight of a pay loader.

Nogueira notes that it is best to pile wet co products on a firm surface, such as concrete, to avoid contamination from the soil and to prevent nutrients from leaching and percolating into the ground. He notes that covering the bunkered co products not only prevents spoilage, but protects the co products from rain, the accumulation of which might result in runoff or a change in the moisture content of the mix. "Even during the winter, covering them is important," he notes, because WDGS that arrives fresh from the ethanol plant can exceed temperatures of 150 degrees Fahrenheit. "If [warm co-products] are snowed on, this high temperature will melt the snow, resulting in greater effluent losses and increased moisture," he says.

Shrink and Spoilage
To determine how much wet co product might be lost due to shrinkage, the cattle producer might assume between three and six percent for silo bags and between 10 and 14 percent for covered bunkers, similar to silage storage, the UNL researchers said. The Iowa Beef Center notes studies that say WDGS stored in silo bags with 20 percent hay shrink by 7.2 percent after bagging, compared to 14 percent for corn silage and 9.7 percent for haylage stored in bags.

The amount of mold and odor stored wet co products will produce appears to be directly related to the amount of air the co products are exposed to, the UNL researchers said. Bagging WDGS or covering bunkered, compacted WDGS with plastic covers is important due to concerns about the dangers of feeding moldy corn grain to livestock. The researchers say samples of stored WDGS have been tested for the presence of various mycotoxins—including aflatoxins, ochratoxins, vomitoxin, zeralenol, zearalenone, T-2 toxin and fumonisin—and only fumonisin was found in any of the samples, but at a low level. It was not clear whether the fumonisins were produced during storage or whether they were present in the corn grain before it entered the ethanol plant. According to the Iowa Beef Center researchers, species of bacteria can produce mycotoxins on corn and when the grain is processed into ethanol, the mycotoxins are not destroyed, but become concentrated in the co-products.

Ryan C. Christiansen is the assistant editor of Ethanol Producer Magazine. Reach him at rchristiansen@bbiinternational.com or (701) 373-8042.