Agriculture Reference
In-Depth Information
separation process may vary between plants
depending on feedstock. Wet-milling wheat
ethanol plants should determine the choice of
feedstock according to their technical processes
for starch-protein separation, availability, protein
and starch content, and market values of ethanol
and co-products.
Basic standards for feedstock and all other raw
materials, and strict adherence to these standards,
are critical for smooth operation of the plant and
quality assurance. The basic standards for feed-
stock should at least include limits of moisture
content, starch and protein ranges, and tolerant
levels for mycotoxins and other contaminants.
Special attention should be given to mycotoxins
as they tend to be concentrated severalfold in the
co-products of vital wheat gluten, gluten meal,
gluten feed, germ or germ oil, and DGS. The
FDA has set limits for some of the common
mycotoxins, such as afl atoxins, vomitoxin, fumo-
nisins, and zearalenone in animal feeds. Wheat is
well known for its susceptibility to Fusarium
toxins (vomitoxin and zearalenone); therefore,
quality standards must be enforced to prevent
toxin-contaminated feedstock from entering the
plant.
potential of a feedstock. Most ethanol plants are
equipped with an HPLC system, which can accu-
rately determine the content of important compo-
nents in the fermentation process, such as glucose
and other sugars, ethanol, glycerol, acetic acid,
and lactic acid. With these timely data in hand,
engineers can closely monitor fermentation
and other production processes and take immedi-
ate corrective or preventive measures when
necessary.
Recent advances in technology
Technology development in the ethanol industry
has lowered the production cost of fuel ethanol
and made ethanol competitive on the energy
market. The most signifi cant technological
advances include enhanced feedstock quality
(grain yield and ethanol yield), improved charac-
teristics of fermentation organisms, and reduction
in energy and water consumption. Because 95%
of the fuel ethanol in the US is produced from
maize, innovations in ethanol production
mostly impact the dry-grind process of maize
(Rendleman and Shapouri 2007). Some innova-
tions could be applicable directly, or after some
modifi cation, to the dry-grind process of wheat.
However, most of the innovations described
below are still in the developmental stage and
have not been used in commercial production.
Evaluation techniques for feedstock and
co-product quality
Currently, near infrared spectroscopy (NIRS)
equipment is widely accepted in the fuel ethanol
industry for instant measurement of moisture,
protein, and starch content. It plays an important
role in an ethanol plant, by allowing quality-
assurance personnel to make on-site decisions as
feedstock is delivered. Because accuracy of NIRS
data largely relies on accuracy of the reference
method and the completeness and size of the cali-
bration database, NIRS readings for moisture and
protein content are more reliable than starch
estimates.
As reported by Wu et al. (2007), different
starch sources differ in ethanol production poten-
tial. Ethanol yield from cereals with similar starch
content can be signifi cantly different. Only labo-
ratory fermentation tests, which may take four to
fi ve days, can accurately evaluate ethanol yield
Fermentation technology
Most dry-grind plants operate on a batch basis.
Some wet-milling plants run continually for
several months to a year. Continuous operation
provides cost-savings on equipment, mainte-
nance, labor, and yeast; avoids peak utility
demand; and achieves higher ethanol yield.
Ingledew (2003) and Warren et al. (1994) provide
more justifi cation and features of continuous
ethanol fermentation.
Development of new fermentation microor-
ganisms with improved features, such as tolerance
to higher ethanol concentrations (up to 18%-
23% v/v) and higher temperature (up to 60 ºC),
has greatly improved fermentation effi ciency and
speed in the past decade. Because fi ber in DGS
is considered a limitation for its application in
