**3. Chemical composition of distiller grain**

in the world during the last decade wheat grain has been used as second feedstock after corn for ethanol production due to its high starch content. Many different classes and types of wheat can be used for ethanol production. In general, soft wheats such as soft white and soft red classes are preferred to hard wheats because they contain higher starch content. Varieties with higher protein are less desirable, but may still be used when blended with one or more

Increase of fuel ethanol production has resulted in a significant increase in the use of distiller grains in the diets of livestock animals, especially in ruminant feeding. Distiller grains have historically been used as a protein source for dairy cattle. Whereas, increased supply and reduced cost make it also a source of energy to replace grain. The distiller grain has comparable energy value to its original grain, high quality protein and high fibre content but highly digestible which is suitable for ruminant feed but not suitable for monogastric animals or poultry because of high fibre content. Wheat distiller grain is the major by-product of ethanol production when wheat grain is used as a substrate for ethanol production. In the last decade, research has documented the variation in chemical composition of wheat distiller grain, and its feed value as protein, energy or fibre source for dairy and beef cattle as well as small ruminant animals. Studies have frequently focused on comparing the feed value of wheat distiller grain to corn distiller grain and characterizing the impact of inclusion of these by-products on nitrogen and phosphorus excretion in manure. To our knowledge, there is no review article that has addressed these research findings, even though several review articles on the use of corn distiller grain in animal production and one book chapter on use of wheat distiller grain in pigs and poultry have been published [2, 3]. The objective of this chapter is to describe some recently developed knowledge and application of wheat distiller grain in ruminant

There are two main distillery processes, dry-milling and wet-milling distillery. The dry-milling process is the main process for producing ethanol [4]. The dry-milling process includes primarily the follow steps: grinding or milling, liquefaction, saccharification, fermentation and distillation [5]. The grain is ground to produce bran-free flour, and then mixed with water and enzymes (amylases) to produce a mash (liquefaction). The saccharification is conducted by adding enzymes to the mash to transform starch into dextrose. After saccharification, yeast is added to start the fermentation process to produce a 'beer' and CO2

beer is separated through a continuous distillation column to yield alcohol [5]. The remaining material is called whole stillage and consists of all the components of the original grain (except the starch), yeast and added water. The whole stillage is centrifuged to produce wet distiller grain (solid fraction) and thin stillage (liquid fraction). The wet distiller grain contains 30–35% dry matter, while thin stillage has only 5–7% solids. The thin stillage is concentrated through evaporation into condensed distiller solubles, which are mixed with wet distiller grain and dried to become dried distiller grains with solubles, which are the most

. The

high starch varieties.

294 Wheat Improvement, Management and Utilization

animal diets.

**2. Production of distiller grain in ethanol plant**

During ethanol production process, starch is mostly converted into ethanol and it leaves all other components of grain to be condensed. Therefore, compared to the original wheat grain, starch contents of distiller grain is very low (4.3%), whereas the contents of non-fermentable components including crude protein, neutral detergent fibre, acid detergent fibre, ether extract and phosphorus are considerably higher (**Table 1**). The primary nutrient contents of wheat distiller grain are crude protein and neutral detergent fibre ranging from 30 to 45% or from 25 to 55%, respectively. The chemical composition of wheat distiller grain can vary considerably depending on numerous factors mainly including wheat source and technology used in ethanol plant (**Table 2**). Physical and chemical characteristics of grain vary with


**Table 1.** Chemical composition of original wheat and wheat distiller grain (% of dry matter).


**Table 2.** Mean values, standard error and range of nutrient content of DDGS.

grain source (variety, growing conditions, etc.), which thus directly affect the composition of distiller grain. Furthermore, the variations in nutrient content of wheat distiller grain have not only been reported from plant to plant, but also from batch to batch [6]. The differences among ethanol plants could be substantial according to the method of grain preparation with or without previous de-hulling, the fermentation conditions, drying method, duration and temperature of drying, amount of solubles added back to wet distiller grain and grinding procedure used. All these can potentially contribute to the product variability. The quantity of solubles added to wet distiller grain pre-drying is easily controlled process but it also can potentially create the variability in wheat distiller grain [6]. Solubles are high in fat (up to 34% of dry matter) and low in neutral detergent fibre, therefore, the more solubles are added to wet distiller grain, the higher the fat and the lower the neutral detergent fibre content. The heat damage is another source of variability and it occurs during the drying process. Wheat distiller grains that have undergone high processing temperature will have a reduced protein degradability in ruminants. The heat damage can be easily checked with the colour of distiller grain which varies from light yellow to dark brown. Cozannet et al. [7] measured the luminance values of 10 European wheat distiller grains and it ranged from 43 (black products) to 63 (yellow products) using a Minolta colorimeter. These authors indicated that wheat distiller grain with luminance values <50 was overheated, which will have a high incidence of Maillard reactions.

The amino acid profile of protein is an important nutrition attribute to ruminant animals. We observed that protein of wheat distiller grain had amino acid profiles partly in agreement with that of the initial grain [8]. Li et al. [8] reported that the changes in amino acid profiles from the original grain to its distiller grain did not follow the same trend as changes in the crud protein; proportion of amino acid increased for some, and decreased, or remained unchanged for others. Han and Liu [9] suggested that the amino acid from yeast source during ethanol fermentation would have important influences on amino acid profiles of distiller grain. Yeasts used for starch fermentation represent an additional protein source equivalent to about 5% of the total distiller grain protein content [10]. Theoretically, yeast cannot hydrolyse protein from grain to free amino nitrogen due to the lack of extracellular proteolytic activity [9]. Li et al. [8] discussed that the differences in amino acid composition between the original grain and its distiller grain also depends on the amino acid composition of the yeast used in ethanol fermentation. In fact, it was reported that yeast protein could contribute up to 20% of the protein in distiller grain, and that amino acid profiles of yeast protein were different from those of grain protein [9]. In addition, the level of soluble fractions added into distiller grain is another source influencing the protein content and the amino acid profile. Cozannet et al. [7] reported that although amino acid profile is quite comparable in wheat and wheat distiller grain, lysine and arginine are lower for wheat distiller grain, and the lysine and arginine levels in the crude protein of wheat distiller grain are highly variable, even in light-coloured products: 1.7–3.0% and 3.7–4.6%, respectively.

The considerable variability in chemical composition of wheat distiller grain is one of the main issues challenging in feed formulation for precisely feed livestock animals. Hence, in practice, a determination of nutrient contents of wheat distiller grain from each delivery is recommended if the nutrient profiles are not provided.
