Ethanol production plant
Ethanol production plant

Distiller Grains

Ethanol production has increased in recent years. As a result, distillers grains (DG), i.e. by-products of ethanol production, have gained importance as an output for ethanol producers and an input for livestock producers.

Ethanol production

In order to produce alcohol, an ingredient high in sugar (grains, fruits or vegetables) is combined with yeast and water and allowed to ferment. The food ingredient used is dependent on the desired end product. Ethanol is sometimes referred to as grain alcohol because it is the main type of alcohol produced by grain fermentation.

(1) Milling

A grain (e.g. corn or barley) has a high starch content which is used for alcohol production. All grains must be either dry milled or wet milled to expose the starch.

(2) From starch to glucose

The starch must be broken down into simple sugars. The meal is soaked in water and enzymes (e.g. amylase) which break the starch down into simple sugars as the starch is heated. Ammonia is added to control the pH and as a nutrient for the yeast. The mixture is processed at high temperatures to reduce the bacteria content.

(3) Fermentation

Once the starch has been broken down, this mixture, or mash, undergoes fermentation whereby the yeast is added to convert the sugar to alcohol. The yeast fungus splits the sugars (e.g. glucose) into ethanol molecules (alcohol) and carbon dioxide molecules. The carbon dioxide rises from the fermenting solution and is removed from the fermentation tanks, while the ethanol accumulates in the “stillage”.

(4) Distillation

Once fermentation is complete, the stillage (alcohol, water and solids) are transferred to distillation columns where the alcohol is removed. In the distillation columns, the remaining stillage, known as distiller grains, are pumped out of the bottom. As they are pumped from the bottom of the distillation column, the water and alcohol are heated which causes the alcohol to evaporate. The alcohol is evaporated in its gaseous form and transferred to a second distillation column. This heating and purifying is repeated several times in order to remove sufficient water. Finally, to purify the alcohol further, it can be run through a molecular sieve as alcohol molecules are larger than water molecules.

Distiller Grains

The by-product of ethanol production, known as distiller grains, are pumped from the distillation column and run through a centrifuge to separate the liquid from the solids. These solids are known as wet distiller grains. These wet distiller grains can be marketed as wet distiller grains, or dried and marketed as dried distiller grains. The liquid (which was separated in the centrifuge) is evaporated, producing a thickened syrup with high nutritional value for livestock. This syrup, known as condensed distiller solubles (CDS) can be sold directly into the animal feed sector; or added back into the wet or dry distiller grains to produce distiller grains with soluble (DDGS). DDGS contain a high content of crude protein, fat and crude fibre, but have a lower starch content. Due to this nutritive profile, DDGS can be used as an animal feed ingredient.

What we would like you to do

Please reflect on this article and share your thoughts with your fellow learners in the comments section below:

  • Have you ever heard of dried distiller grains before?

  • Did you ever think by-products of alcohol production could be used in animal feed?

  • Do you think the use of by-products of alcohol production in livestock feed is advantageous?

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This article is from the free online course:

Animal Feed Production: Feed Safety

EIT Food