Biofuel Co-Products as Livestock Feed

Figure 1. The process and co-products of a dry-grind cereal ethanol plant.
Grain
Dry Grinding
Threefold concentration
Ethanol
Residue
(protein, fibre, fat, minerals,
remnants of yeast from
fermentation )
Centrifuge
Wet Distillers Grain (WDG)
Thin Stillage
(TS) (liquid)
Condensed Distillers
Solubles (CDS)
Wet Distillers Grain plus Solubles (WDGS)
Dry
Distillers Dried Grain plus Solubles (DDGS)
The co-products from dry-grind cereal ethanol plant (see Fig 1) are described as follows:
Whole stillage - the material left after the extraction of ethanol. A slurry, 10 – 25% Dry Matter (DM),
it contains all the insoluble and soluble non-starch components of the grain together with the yeast
remnants from fermentation. It is not used as such as a livestock feed, but is pressed or centrifuged to
separate the liquid portion, thin stillage, from the ground grain solids, wet distillers grain.
Thin stillage (TS) (4 – 8% DM) contains both suspended and dissolved nutrients. On a DM basis, it is
high in Crude Protein (CP), fat, minerals and digestible fibre (see Table 2). The amino acid
composition of a given cereal TS is close to that of the original cereal (Mustafa, McKinnon et al.
2000). In ruminants, 52% of thin stillage has been found to bypasses the rumen (Iwanchysko,
McKinnon et al. 1999) which is then available for digestion in the lower gastrointestinal tract. The
bypass process for TS is thought to be due to closure of the oesophageal groove and failure of the TS
to equilibrate with the rumen contents.
Condensed distillers solubles (CDS) is concentrated TS (25 – 50% DM) following evaporative
concentration using a multi-effect falling film method to conserve energy and to minimise heat
damage to the nutrients. CDS has been trialled as an energy source for finishing cattle (Rust 1990), but
is usually added back to wet distillers grain for use in the wet (WDGS) or dry (DDGS) form.
Wet distillers grain (WDG) also known as wet cake consists of ground grain and yeast solids left
following the separation off of thin stillage from whole stillage. WDG has limited storage time and is
costly to transport due its high moisture content (25 – 35% DM). Below 8°C it can be stored for 7 – 10
days, but at 22°C this is reduced to 3 – 5 days (Walker 2004). It is a good source of protein and energy
for ruminants particularly when condensed distillers solubles are added back to form wet distillers
grain plus solubles (WDGS).
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