are the main grain resources in china? Describe the main processing of a
typical grain (wheat or rice)
main grain resources in china are rice,
wheat, corn, millet, barley sorghum.
The main processing of wheat begins with the
milling of the grain into flour. Flour is the value added product procured from
wheat. Several steps are done during wheat processing and these are; product
control- this entails the testing of the product on whether it not damaged by
pests and there is no insect infestation. A sample is obtained, classified,
milled and baked to determine the end use quality. The results from the quality
control chemists will then determine how the wheat is processed and stored.
The second phase during processing is when
the grains undergo cleaning. This is the stage whereby unwanted particles like
stones, metals, sticks, grasses just to mention but a few are removed. This
stage also involves the use of the magnetic separator which traps all the
metallic substances. The separator then removes all the big and small
substances in the wheat. The dust particles are eliminated by the use of an
The wheat is then introduced into a de-stoner
which separates the stones from the grains using gravitational force. The
stones will fall first due to a dissension in weight. Wheat kernels are then
passed through a disc separator which then separates the wheat basing on size
and shape. Smaller and bigger, round and angular grains are removed since they
will affect the milling process and they might be harbors of fungal infections.
The final stage during cleaning is the scourer where dehusking takes place.
The third stage is when wheat is conditioned.
This is achieved by adding moisture to wheat grains in precise amounts to
toughen the bran and soften inner endosperm. The addition of moisture helps the
parts of the kernels to disunite more easily and clearly. Conditioned wheat is stored
in bins for 8-24 hours depending on type of wheat. Wheat blending is the
employed to accomplish the desired flour quality for a specific end use.
During conditioning the wheat is then passed
through impact scourer where centrifugal force breaks apart the defective
kernels and repudiate them from the mill flow. The wheat is then passed to the
grinding bins, large hoppers that will measure and feed the wheat to the actual
Wheat grinding then follows. The wheat
kernels are measured and fed from the bins to the rolls made from chilled cast
iron. The main objective of introducing the wheat to the rolls is to produce
middlings or coarse particles of endosperm. The coarse endosperm particles are
separated from the bran by sieves and purifiers. During milling, the miller
must select the exact milling surface on the break rolls as well as the
reletion and the speed of the rollers to each other to match the type of wheat
and its condition. The break rolls are systematically set to produce purest
endosperm and the middlings rolls also set to produce as much flour as
possible. The ground wheat is send upstairs to drop through sifters. The ground
wheat is moved via pneumatic systems that mix air with the particles so they
flow almost like water through tubes.
The broken wheat kernels are introduced into
sifters which are large, rotating box like where shaking will be taking place
through a series of bolting cloths or screens to separate the larger particles
from the smaller particles. Inside the sifters are small frames which may be
covered by nylon or stainless steel screens with square openings that get smaller
and smaller as they go. During sifting, the larger particles are shaken off
from the top or scalped leaving the finer flour to sift from the bottom. The
scalped fractions are sent to the other roll passages and particles of
endosperm and are graded by size and carried to separate purifiers.
In a purifier, a controlled flow of air is
used to lift the bran particles while at the same time bolting cloth separates
and grades coarser fractions by size and quality. The process of sifting to
purifying is repeated several times to obtain a maximum amount of flour, consisting
of 75% of the wheat. The remaining percentage of the wheat grain is grouped as mill
feed thus shorts, bran and germ.
After purifying, wheat flour undergoes
reconstituting or blending back together where all parts of the wheat in the
proper proportions yields whole wheat flour. Reconstituting ensures that the
wheat germ oil is not spread throughout the flour and does not produce a bad
taste and odor.
Towards the end of the processing process of
wheat flour, the flour is bleached, thus exposing it to chlorine gas or benzoyl
peroxide to whiten and brighten flour color. Chlorine also has a bearing on the
baking quality by maturing or oxidizing the flour which further poses positive
effects on cake and cookie baking. The bleaching process does not destroy the
nutrients and is not dangerous to humans during consumption.
The final and last stage during wheat flour
processing is the enrichment. The flour passes through a device that measures
out the specified enrichment quantities. For self-raising flour, a leavening
agent (yeast), salt, malt and calcium are added in known amounts. Laboratory
tests are also performed to ensure product safety. The flour is then passed
through pneumatic tubes to the packing room or into hoppers for bulk storage.