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Dairy Focus: Manage Wet Byproducts to Prevent Spoilage

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J.W. Schroeder, NDSU Extension dairy specialist J.W. Schroeder, NDSU Extension dairy specialist
NDSU’s dairy specialist provides tips on storing wet distillers grains.

By J.W. Schroeder, Dairy Specialist

NDSU Extension Service

Editor’s note: This is the 10th article in a series on the issues facing the region’s dairy farmers, particularly the impact of the growing ethanol industry.

Many livestock producers will get on the wet distillers grain bandwagon as more and more products become available.

Early in the process, many dairy producers have enjoyed the cost savings of using wet distillers grains (a byproduct of the ethanol production process) for energy, protein and digestible fiber. However, two major factors are limiting their use.

  • High moisture content (60 percent to 70 percent water) limits the distance wet distillers grains can be shipped from the ethanol plant economically.
  • Aerobic stability is poor in warm weather, limiting delivery to small quantities that must be fed quickly. Spoiled wet distillers grain can be extremely unpalatable and cause reduction in nutrient intake when fed to livestock.

During the production of ethanol, a significant amount of heat is used to gelatinize the starch that also kills many undesirable microorganisms. Distillers grains essentially are sterile after processing, but may have low numbers of residual yeast. Distillers grains come out of the centrifuge hot and are dropped on a storage pad, loaded on trucks and finally unloaded on the farm.

This is where the problem lies. If any of those surfaces are not clean and periodically disinfected, yeast and bacteria are inoculated into a sterile product. Yeast will double in number in one hour; thus, wet distillers grains contaminated with 100 of the unicellular fungi per gram under optimal conditions could have more than 100,000 per gram in less than 10 hours and 1.6 million per gram in 14 hours.

Yeasts primarily are aerobic microorganisms and, thus, exposure to air stimulates growth. Residual amounts of sugar and some starch in distillers grains provide sufficient nutrients. Yeast generally starts the molding process by metabolizing sugar and starch, which raises the temperature and pH (acidity). This improves the environment for bacteria and mold to flourish, setting up conditions for massive spoilage.

Reducing spoilage of wet distillers grain starts at the ethanol plant since it comes out of the digesters nearly sterile. From then on, how it is handled determines how quickly it spoils.

Sanitation and periodic disinfecting of the pads and trucks is important. Reducing exposure to air is critical. In warm weather, bagging or covering wet distillers grains with a tarp on the storage pad will minimize exposure to air. Store it out of direct sunlight to minimize heating.

Organic acids, such as acetic, propionic, sorbic and benzoic acids, act best to inhibit yeast and molds. However, more research is needed to better understand and develop strategies for improving the stability of wet distillers grains.


NDSU Agriculture Communication

Source:J.W. Schroeder, (701) 231-7663, jw.schroeder@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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