Agriculture Reference
In-Depth Information
inconsistent, suggesting that additional breeding
effort could overcome this defi cit (Guttieri et al.,
2006b). Application of low-phytate mutants in
wheat breeding promises the development of a
more nutritious class of feed wheat, with dimin-
ished
Table 22.2
Percentage of all grain based fuel ethanol pro-
duced in the US from two primary processes.
Year
Wet-Milling Process Dry-Grind Process
------------------ % -----------------
release
of
phosphorus
into
the
2001
50
50
environment.
Waxy wheat also has potential advantages as a
feed source. Animals that have a low feed-conver-
sion ratio are considered more effi cient users of
feed for increasing body mass. Broiler chickens
fed a diet of waxy wheat had lower feed conver-
sion ratios than birds fed wild-type samples (Pir-
gozliev et al., 2002). Kim et al. (2005) found
improved starch digestibility in swine fed waxy
wheat. Breeding efforts to combine the low
phytate and waxy traits should result in a superior
type of feed wheat.
2002
40
60
2003
33
67
2004
25
75
2005
21
79
2006
18
82
Source:
(Renewable Fuels Association 2006, 2007).
maize, wheat ethanol plants may differ in many
ways from maize ethanol plants (Warren et al.,
1994).
Although both wheat and maize wet-milling
processes have been used for ethanol production,
they differ in how the protein is separated
from starch. In maize wet-milling, the starting
material (maize kernels) is fi rst soaked in
sulfur dioxide solution for 24 to 48 hours. The
separation procedure following grinding is
focused more on germ oil and starch for food
markets than on maize protein which is used for
animal feed. Products from ethanol production
in maize wet-milling plants are typically
ethanol, gluten meal, oil, gluten feed, and fi ber
(Fig. 22.2).
Wet-milling of wheat uses mostly wheat fl our
as starting material, and the separation process is
focused more on wheat gluten. Separation of
wheat protein and starch from wheat fl our is
based on their water insolubility, density, and
particle size. Four processing technologies
[Martin, Alfa-Laval/Raisio, hydrocyclone, and
high-pressure disintegration (HD)] have been
used industrially in the wet-milling of wheat
fl our. The fi rst three processes are more common
in North America, and the HD process is more
popular in Europe (Cornell and Hoveling 1998;
Sayaslan 2004). Therefore, the protein-starch
separation section of a wheat wet-milling ethanol
plant is very different from that in a maize wet-
milling ethanol plant, and may vary between
plants. Downstream processes from starch to fuel
Wheat conversion to ethanol
New market for wheat in ethanol industry
United States fuel ethanol production increased
300% from 2000 to 2006, with an annual output
of 18.5 billion liters in 2006. Of this, 95% was
produced from maize, approximately 4% from
grain sorghum [
Sorghum bicolor
(L.) Moench],
and less than 1% from wheat and other feed-
stocks. However, wheat has been used as a major
feedstock for fuel ethanol production in Europe
(70%) and Canada (15%), and wheat ethanol pro-
duction will continue to increase in those coun-
tries (Smith et al., 2006).
Both wet-milling and dry-grind processes can
be used for ethanol production from wheat.
Because investment and operating costs for dry-
grind plants are about one-half those for wet-
milling plants, most of the recently built,
small-to-medium size ethanol plants are dry-
grind plants. Consequently, the percentage of
fuel ethanol produced by the dry-grind process
rose from 50% in 2001 to 82% in 2006 (Table
22.2), while ethanol production by the wet-milling
process decreased (Renewable Fuels Association
2006, 2007). Because physical and chemical prop-
erties of wheat and functional characteristics of
wheat components are different from those of
