RA 00048.pdf - OAR@ICRISAT

A
D
B
C
E
Figure 2. The United Milling Systems DVA sorghum
dehuller (Munck et al. 1982).
nets are conveyed by a screw (C) into the
decortication chamber (D), where a steel rotor
rotates the grain mass towards the cylindrical
screen (F). The pressure between the seeds
during decortication can be controlled by the
counterweight (G) in the outlet (H). The hulls and
the endosperm fragments from the cracked kernels
are discharged through the screen by an air
current at high pressure. This fraction—the
screen flour—is sucked out from the bottom of
the machinery into a cyclone.
The first crucial point in the new dehulling
process is described in Figure 3, where the UMS
DVA decorticator is integrated into a milling
system with a capacity of 2 t/hr. This is done in
order to recover endosperm particles from the
screen flour. After separating the fine bran fractions
from the coarse ones through sifting (A2),
the coarse fractions are separated by aspiration
into an air sifter (B1) producing coarse bran (B2)
and cleaned endosperm fragments (B3). The latter
could then be milled together with the decorticated
kernels (C1) in a milling and sifting section.
Thus grits and flours of a high yield are produced.
Products from the various stages in this process
are displayed in Plate 1:d.
F
G
H
The new UMS DVA dehuller can, depending on
the processing conditions, remove whole
embryos, which produce sharp-edged decorticated,
degermed kernels resembling children's
milk teeth. This indicates that the UMS DVA
dehuller produces a small amount of fine endosperm
flour compared with abrasion mills, which
tend to produce round seeds. Seeds decorticated
with abrasive stone mills are more rugged on the
surface and thus appear whiter than seeds from
the UMS DVA decortication, which still have intact
natural endosperm surfaces. Obviously the rugged
surface indicates losses of fine particles of
endosperm. Breakage of kernels does not affect
yield in the new milling process as much as when
the abrasive polishing technique is used. The
reason is that, in the new process, losses can
always be regained from the screen flour, as long
as the endosperm particles are kept sufficiently
coarse. For example, grains of Lulu D milled in the
new process (Table 1) yield 7 8 % of decorticated
grains and 2% of endosperm fragments, rendering
a total yield of 8 0 % with lighter color than flour
of the same variety milled locally in Tanzania
yielding about 50%.
It is also seen that the yield in the product from
Lulu D of the most important nutrients, starch and
protein, in the new process is 93% and 77%,
respectively. These figures are comparable with
the yield from the hand pounded local hard
Tanzanian sorghum varieties and much higher
than the yield of these nutrients in the hand
decortication of the high yielding Lulu which has a
soft endosperm.
From a nutritional point of view, pericarp and
testa should be removed in the decortication
process, as they contain very small amounts of
available nutrients (Eggum et al. 1982). They are
also the main contributors to color in the final
product. With the new milling process it is
possible to retain most of the nutritious germ if
desired, or remove it completely while processing
sorghum for brewers' grits.
Utilizing high-tannin sorghums with a thick testa
layer is very difficult. Tannins are nutritionally
detrimental as they drastically lower the digestibility
of starch and proteins. They are also potent
carcinogens. In countries in Africa, high-tannin
sorghum types are mainly used for beer. Plate
1 : a (1) displays a mixed sorghum sample consisting
mainly of chalky, white sorghum seeds from
Africa. Under the white pericarp these seeds have
a dark testa layer (Plate 1 :b). Due to weathering,
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