Processing
of cereals
The main purpose of primary processing
of whole cereal grains is to separate the outer layers of the grain from the
inner section. When the grain is milled to produce white flour, the germ and
the bran are discarded. The milling process grinds and pounds the grains. The
process used for milling each grain type is slightly different.
After milling of the
grain, the products can be described in the following ways:
·
Wholegrain or wholemeal products means the whole of the grain has been
used that is the bran germ and endosperm. Because the oil component in the germ
can go rancid after a time, wholemeal products can develop off flavours.
·
Refined products refer to products made only from the endosperm
(starch). The bran and germ are removed. Refined products have a longer shelf
life but are nutritionally poor because they contain mostly carbohydrate.
·
Enriched products have vitamins and minerals added, usually to give them
similar nutritive properties to wholemeal products, but without the fibre
content.
·
Flour is the powdered form of the grain after grinding or milling.
·
Meal is a more coarsely ground product than flour.
·
Instant or quick-cook products have beencooked, orpartiallycooked,
then dehydrated. When reconstituted they require very little preparation time.
Examples include instant porridge, quick-cook rice and instant Asian style
noodles.
Secondary processing
of cereals results in a variety of products. The main products are as follows:
·
Breakfast cereal production may involve other processes such as
rolling and baking to make flakes. Eg. Wheat flakes.
·
Bread and other bakery items such as savoury crispbreads, sweet
biscuits, cakes and pastries require the additional processes of sifting,
mixing, kneading, proving and baking. Some breads and cakes are leavened with
raising agents such as yeast and baking powder.
·
Extruded snack foods— commercially produced using a dough or
batter that is extruded and cooked into novelty shapes. Eg. macaroni.
·
Pasta is formed from flour-based dough and formed into shapes by
hand or machine.
·
Noodles and dumplings are manufactured from flour-based doughs
and shaped, then simmered or poached in liquid.
Cereal processing is
complex. The principal procedure is milling, i.e., the grinding of the grain so
that it can be easily cooked and rendered into attractive foodstuff. The steps
involved in the process of milling are:
·
Rice is passed through two stone rubber discs rotating at
different speeds and by shearing action on the grain, the hull is pulled away.
·
This is then milled in a machine called pearlor to remove coarse
outer layers of bran and germ by the process of rubbing, resulting in
unpolished milled rice.
·
Unpolished rice is liable to develop rancidity and so it is next
polished in a brush machine which removes the aleurone layer and yields
polished rice.
·
Sometimes the polished rice is further treated in a device known
as trumbol to give a coating of sugar and talc to produce a brighter shine on
the rice.
The percentage of
losses of different nutrients during milling are: protein 15 percent, fat 82
percent, thiamine 85 percent, riboflavin 70 percent and pyridoxine 50 percent.
The degree of milling determines the amount of nutrients removed.
Parboiling is a
process in which rice has been partially boiled in the husk.
This makes rice easier
to process by hand, boost its nutritional profile and change its texture.
·
Steeping paddy in cold for 2 or 3 days
·
in large cement tanks.
·
Steaming of the soaked paddy for 5-10 minutes, and
·
Drying in the sun.
·
Soaking of paddy in water at 65-70o C
·
for 3-4 hours.
·
Draining of water and steaming of soaked paddy in the same
vessel for 5-10 minutes, and
·
Drying of the paddy in the sun or in mechanical driers.
·
Dehusking of parboiled rice is easy.
·
Milled parboiled rice has greater resistance to insects and
fungus.
·
Loss of nutrients due to the removal of husk and bran in milling
are decreased.
·
Loss of water soluble nutrients due to washing of rice is less
in parboiled rice compared to raw rice.
·
Parboiling improves digestability.
Malting is a
controlled germination process, which activates the enzymes of the resting
grain resulting in the conversion of cereal proteins and other macromolecules.
Generally barley is
used in the production of malt. Other grains used in the preparation of malt
includes wheat, jowar and ragi.
The process of malting
of cereal grains consists of the following steps:
a. Selection of grain and
cleaning.
b. Steeping in cold water
for 36 hours with 2 to 3 changes in water.
c. Germination: The
grains are spread on wire mesh trays and kept for 3 days. Water is sprinkled
over each of these trays.
d. Kilning: The
germinated grains are dried at slow rate on kilns.
Amylase rich food
(ARF) is germinated cereal flours which are extremely rich in the enzyme alpha-amylase.
ARF are excellent weaning foods because they reduce the bulk of weaning foods
and are energy dense. Malt is used in commercial proprietary foods, breakfast
cereals, malted milk confectionaries, infant foods, bakery products and in
brewing.
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