Utilization of Bio-fuel Co-products
Several different feed co-products can be derived from ethanol production depending on where in the production process they are derived. Several processes are involved in ethanol production including grinding, cooking, liquefaction, fermentation and distillation. Once the ethanol has been distilled off, the remaining material is referred to as whole stillage. Whole stillage is centrifuged into two fractions: coarse solids, or wet distillers’ grains (WDG), and thin stillage. Wet distillers’ grains can be fed to livestock in the wet form, or dried to produce dried distillers’ grains (DDG). Thin stillage can also be utilized or evaporated to produce condensed distillers’ solubles, or ‘syrup’. The condensed distillers’ solubles may be added back to the dried distillers’ grains to produce dried distillers’ grain with solubles (DDGS).

The nutrient content of DDGS produced from wheat is quite different from that produced from corn. Wheat DDGS is typically higher in protein and fibre, but lower in fat than corn-based DDGS. Consequently, corn DDGS tends to have higher energy values than the wheat-based product.

Nutrient profile comparison of corn and wheat DDGS


Corn DDGS * 

Wheat DDGS ** 

Moisture 10 8 to 10
Crude Protein % 30.9 34.9
Undegradable Intake Protein (% of CP)  44 to 52 45 to 54
TDN % (ruminant) 86.0 82.0
DE Kcal/kg (swine)  4075 3500
Crude Fibre %  7.2 12.6
Ash % 6.0 3.3
Fat (ether extract) % 10.8 6.6
ADF % 12.2 16.4
NDF % 44.0 43.0
Calcium % 0.07 0.12
Phosphorus % 0.77 0.63
Available P % (swine) 0.18 0.20
Lysine % 0.91 0.87
Threonine % 1.14 0.97
Methionine + cystine % 1.30 0.95
Tryptophan % 0.24 0.22

* University of Minnesota website: » http://www.ddgs.umn.edu/
** Feeds Innovation Institute (2006): » http://feeds.innovation.usask.ca/

Below is a flow chart explaining the process of ethanol production using dry milling processes for corn. The same dry milling process is used in ethanol production from wheat. In the first step, water is added to ground grain to form a slurry which is heated to a relatively high temperature in the liquefaction process (this temperature is variable but can be as high as 150˚C followed by a holding period at >90˚C). Heat stable starch degrading enzymes (alpha-amylase) are also added during this step. After liquefaction, the mash is cooled and gluco-amylase is added to convert the liquefied starch to fermentable sugars (dextrose). The cooled mash enters the fermentation tanks where yeast is added to ferment the sugars, producing ethanol and carbon dioxide. At the end of fermentation, the beer leaving the fermentation tanks is directed through a distillation system which removes the ethanol, leaving a product know as ‘whole stillage’. The whole stillage is centrifuged to separate the solids (wet distillers’ grains) from the liquid fraction containing solubles (thin stillage). An evaporation step is used to remove excess water from the thin stillage, leaving a condensed syrup which is then mixed back with the wet distillers’ grains and dried to produce the distillers’ dried grains with solubles (DDGS).