Grain processing affects byproduct nutritive value | TSLN.com

Grain processing affects byproduct nutritive value

Dr. Greg Lardy

Courtesy photoDr. Greg Lardy

Byproducts (sometimes known as co-products), in particular things like dried distillers grains plus solubles, corn gluten feed, soybean hulls, and wheat middlings, are increasingly available in large quantities in this region.

In this column, I’ll describe how two byproducts – distillers grains plus solubles and wheat middlings – are produced and how processing methods influence their nutritive value. You should then be better equipped to make informed decisions about using them on your livestock operation.

Grain and oilseed processing

Knowing what the processor wants to extract is the first step in understanding the nutritional makeup of the resulting byproduct. In general, most grain and oilseed processors attempt to extract either starch or oil. For example, in soybean processing, the goal is to extract the oil that is destined for the human food market. In ethanol production, the goal is to turn corn starch into fuel grade alcohol (ethanol). In most cases, processors extract starch or oil. The remaining materials (generally fiber, protein, and minerals) are more concentrated in the remaining byproduct than in the original grain or oilseed.

Another thing to keep in mind is that the process used varies between plants and companies. For example, in the ethanol industry, some companies extract corn oil from distillers grains plus solubles to market the oil for other uses. The oil extraction process results in a distillers grains product that is higher in protein but potentially lower in energy since the oil has been removed.

Many other factors, such as grain source, processing methods, available technology in the plant, and production methods impact the resulting nutritive value of the byproducts. Some companies place considerable emphasis on managing byproducts to reduce variation and improve product quality. Other companies simply see byproduct production as an opportunity to market materials that are not their primary business function. You can expect more variation in the byproducts with this approach. There is nothing inherently good or bad about either strategy. However, it is important to know the company’s philosophy so you know what to expect.

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Distillers grains (wet or dry)

Distillers grains are byproducts of the dry milling industry. They are sold wet (35 percent dry matter), modified (60 percent dry matter), or dry (88 percent dry matter).

As the name dry milling implies, corn is hammer milled prior to the addition of water. The proper name for this byproduct, according to the American Association of Feed Control Officials Handbook, is corn distillers dried grains plus solubles. In most cases, it is simply referred to as dried distillers grains or distillers grains. You might see it abbreviated DDGS or WDGS for wet distillers grains plus solubles. In this area of the country, corn is by far the most common feedstock used in ethanol production. It is important to note that processors that use wheat, barley, or other cereal grains will produce different byproducts. Generally speaking, corn distillers grains has better digestibility and greater energy content than distillers grains products produced from wheat or barley. Corn fiber tends to be more digestible and corn grain contains more oil resulting in a higher oil byproduct which affects the nutrient content of the resulting distillers grains.

In the ethanol production process, corn is ground and mixed with yeast and enzymes. The resulting fermentation process produces ethanol from the starch in the corn. The mixture is then distilled to remove the ethanol and the remaining mixture is centrifuged to separate the mash from the solubles. Some of the moisture in the remaining liquid byproduct is driven off by heating to create condensed distillers solubles. This is added back to the mash to make distillers grains plus solubles.

This product can be marketed as wet distillers grain plus solubles (sometimes referred to as wet distillers grains), modified distillers grains plus solubles, or dried distillers grains plus solubles. Dried distillers grains can be difficult to pellet due to the fat content. Because starch is removed in the fermentation process to produce ethanol, the remaining nutrients (e.g. protein, fat, fiber, and minerals) in the corn kernel are more concentrated in the remaining byproduct. These byproducts (wet, modified, and dried distillers grains with solubles) contains corn fiber, corn proteins, corn oil, spent yeast cells, fermentation byproducts, and some soluble proteins that result from the fermentation process.

Wheat middlings

Wheat middlings, or wheat midds, are the byproduct of flour or semolina production from either wheat (usually spring wheat in this area) or durum. The millers are interested in removing the flour or starch from the wheat kernel. The resulting byproduct consists of wheat bran, wheat germ, and small amounts of starch. Small amounts of water are added in the milling process to improve efficiency (usually less than 5 percent by weight), but this added water necessitates the use of aeration fans or flat storage to prevent mold development or spoilage.

Wheat midds are a very popular, highly palatable feedstuff. They are very versatile and can be used in many different commercial feed formulations. Because bulk, non-pelleted midds are very difficult to handle in conventional grain handling systems, most wheat midds are pelleted.

For additional information on either of these byproducts, please see these web resources.

General byproduct information:

http://www.ag.ndsu.edu/pubs/ansci/livestoc/as1182.pdf

Distillers grains:

http://www.ag.ndsu.edu/pubs/ansci/beef/as1242.pdf

Wheat middlings:

http://www.ag.ndsu.edu/pubs/ansci/livestoc/as1175w.htm