Pulse processing by om
-
Upload
om-suryawanshi -
Category
Education
-
view
329 -
download
2
Transcript of Pulse processing by om
Dal Milling Process
By
Er. om
Pulses are basically grain legumes. They occupy an important place in human
nutrition due to their high protein content than cereal grains. In Indian dietary
regime it occupies an important place. Since majority of Indians are vegetarians,
they depend largely on grain legumes (pulses) for their dietary protein. Legumes
contribute a major portion of lysine in the vegetarian diet. They are also a fairly
good source of vitamins like thiamine, machine, riboflavin and much needed iron.
Therefore its quality availability to the common man is a major challenge. Since
recovery was poor in traditional technologies, adoption of modern technology will
go a long way in meeting the need of the common man. Jas enterprise offer mini
dal mill machine. This mini dal mill is simple in construction and easy to operate,
maintain and available at very low cost. Mini dal mill machinery consist of
horizontal tapered roller is covered with emery coating, surrounded by a screen
through which the husk is discharged. The shelled pulses are passes through an
aspirating fan on the oscillating sieve unit, where appropriate grading of pulses is
done. It is run on only 2 HP automatic arrangement are made for collection of de
husked and split pulses, un husked and split pulses, un de husked pulses, broken,
husk in separate containers and bags. This machine offers dust free operation, does
not cause pollution, retains proteins, natural shine et cetera.
Advantage and Special Feature of Mini dal mill Suitable for processing of all types
of pulses Easy to operate Operates by 2 HP electric motor / oil engine Recovery of
head pulses - 78% to 80% Recovery of broken - 1 to 3% De husks and splits
almost all pulses retains proteins and natural shine Special provision for bangle
gram (Chana, chickpeas) by stone chakki for de husking and splitting. Automatic
arrangement of collecting of the following in separate containers and bag de
husked and split pulses Un husked pulses Broken Husk Pollution free operation
Compact size (length 1650 mm x width 900 mm x height 1350 mm )
Process of Dal Milling ( Pulse Milling ) Basic processes in dal milling are
cleaning, grading, conditioning, de husking, splitting, and separation, polishing and
bagging. Major variation is involved with de husking process only. Sometimes
linseed oil is also used during dry milling operation to impart shine or better appeal
to the milled dal. The removal of the outer layer of husk and splitting the grain into
two equal halves is known as milling of pulses. To facilitate de husking and
splitting of pulses alternate wetting and drying method is used.
Pulses
↓
Cleaning, chaffs, dirt, etc.
↓
Pitting
↓
Pretreatment with Linseed Oil
↓
Conditioning
↓
De husking and splitting mixture of husk, small broken and powder
↓
Grading
↓
Polishing
↓
Grade I Pulses
Description of various Mini dal mill's Unit of Operations: Cleaning and grading:
This unit consists of a vibratory inclined sieve, hopper, grain collector, waste
collector and motor. The vibratory sieves are providing with different size holes to
match the requirements of the type of dal being process. The vibrations are
inducing by a cam-operated link, which is mounts on a motor driven shaft
Pitting of dalls: An emery roller machine is used for cracking the husk layer and
for scratching of clean pulses passing through it. This is done for loosening the
husk from sticking to the cotyledons in order to facilitate subsequent oil
penetration in the following unit operations. Gradually the clearance between the
emery roller and cage (housing) is narrowed from inlet to outlet. Cracking and
scratching of husk takes place mainly by friction between pulses and emery as the
material is passed through the narrowing clearance. During the operation some of
the pulses are de husked and split which are separated by sieving.
Pretreatment with oil and water: A screw conveyor allows passing the scratched or
pitted material through it and mixing of some edible oil like linseed oil is complete.
The linseed oil is use at the rate of 1.5 to 2.5 kg/tones of pulses (please refer our
guideline for lintel). These are keeping on floors as required to diffuse the oil.
De-husking and splitting of dal: For de husking of conditioned pulses emery stone
coated emery rollers are used. In one pass about 50-75% of pulses are de husked.
De husked pulses are split into two parts. De husked split pulses are separated by
sieving and the husk is aspirated off. Anti shoplifting pulses and tail pulses are
again de husked and milled in a similar way. For complete de husking and splitting
the whole process is repeated two to three times.
Pre milling of dals: To obtain best results during de-husking and splitting of pulses
in the pulse de husking machine in Jas brand mini dal mills, latest model improved
version, pre milling including grading of pulses size wise is very essential. The raw
pulses are first clean of dust, chaff, stones and other extraneous materials. Sieves
grade cleaned pulses or pulses graded and soaked in water in cement's tanks having
6" depth. Height of pulses soaked is 5" and the water level should be 1" above the
pulses. Soak pulses are taken out of the water after specific time and put on the
sieve. Swollen pulses which do not pass through sieve (from which un-swollen
pulses earlier passed through the same) are ready for heaping in shade whereas the
pulses which pass through the same sieves. Then these pulses are ready for heaping
in shade. Degree of happing of swollen pulses in shade should be 30 to 40. This
process should be continuing until the pulses are swill to the desired extent. There
after the pulses are in thin layers in the open sun drying. Duration of sun drying of
pulses vary according to weather condition prevailing at the time of processing.
After sun drying, the pulses are again heap in shade so moisture contents in the
pulses may become uniform as need in them for de-husking. Then the pulse are
graded again fed in to the pulse de husking machine in Jas mini dal mill in graded
lots to achieve he best results with minimum brokenness. For the guidance of the
entrepreneurs, the process of details of pre-milling of pulses after proper cleaning
is show here after in a tabulated chart.
Note: - Period of soaking in water will vary according to weather condition and
quality of pulses. Duration of sun drying will vary according to weather condition.
Pulses should not be warm at the time of De-husking/splitting. Pulses should be
de-husk and split in graded lots only. Pulses shown at one and two must be dry
within 3 days to get better results. Their processing in any season should be
avoiding. The de-husked pulses mixed with the un-husked pulses and the husks are
again de-husked in the Jas brand mini Dal mill as usual. In second pass all, the
pulses are de-husked.
Pulses constitute essential components of vegetarian diet. Pulses are major source
of protein in Indian vegetarian diet. These are main source of protein providing
most of the essential amino acids to a certain degree. Economically, pulses are
cheapest source of protein. Pulses are Bengal gram, pigeon pea, black gram, green
gram, lentil, etc. Pulses are mainly consumed in the form of dehusked split pulses,
as these are rich in proteins. In vegetarian diet pulses are main source of protein.
COMPOSITION
Green gram, red gram, bengal gram, horse gram, cluster bean, field bean, cow pea
are some of the common types of pulses.In general, their protein content is high
and is commonly more than twice that of cereal grains, usually constituting about
20 per cent of the dry weight of seeds. The protein content of some legumes like
soyabean is as high as 40 per cent.
Pulse seeds are also sources of other nutritionally important materials, such as
vitamins and minerals.
Carbohydrates: Food pulses contain about 55-60 per cent of total carbohydrates
including starch, soluble sugars, fibre and unavailable carbohydrates.
Minerals: Pulses are importantly sources of calcium, magnesium, zinc, iron,
potassium and phosphorus.
Vitamins: Pulses contain small amounts of carotene, the provitamin A.
TOXIC CONSTITUENTS OF PULSES
The seeds of pulses include both edible and inedible types. Even amongst the
edible legumes toxic principles occur and their elimination is important in order to
exploit them for edible purposes. Two thermoliable factors are implicated in toxic
effects. Inhibitors of the enzymes trypsin, chymotrypsin and amylase
haemagglutinins, which impede the absorption of the products of digestion in the
gut. In addition, legumes also contain a goitrogen, a toxic saponin, cyanogenic
glycosides and alkaloids.
Elimination of Toxic Factors
It has already been indicated that soaking, heating and fermentation can reduce or
eliminate most of the toxic factors of the pulses. Correct application of heat in
cooking pulses can eliminate most toxic factors without impairment of nutritional
value. Cooking also contributes towards pulse digestibility. Heat causes the
denaturation of the proteins responsible for trypsin inhibition, haemagglutination
and the enzyme responsible for the hydrolysis of cyanogenic glycosides. The mode
of application of heat is important. Autoclaving and soaking followed by heating
are effective. Another way of eliminating toxic factors is by fermentation, which
yields products more digestible and of higher nutritive value than the raw pulses.
Processing: Processing of pulses is of primary importance in improving their
nutritive value. The processing methods used are soaking, germination
decortications, cooking and fermentation.
Soaking: Soaking in water is the first step in most methods of preparing pulses for
consumption. As indicated above, soaking reduces the oligosaccharides of the
raffinose family. Soaking also reduces the amount of phytic acid in pulses.
Germination: Germination improves the nutritive value of food pulses. The
ascorbic acid content of pulses increases manifold after 48 hours germination.
Germinated and sprouted pulses have been used to prevent and cure scurvy. The
riboflavin, niacin, choline and biotin contents of all pulses increase during
germination. The germination process reduces and/or eliminates most of the
antinutritional and toxic factors in several pulses.
Decortication: A simple method is to soak the seeds for a short time in water; the
husk takes up more water than the seeds and may be easily separated by rubbing
while still moist. In the alternative, the soaked grains may be dried and the husk
removed by pounding and winnowing. Roasting also renders the husk easier to
separate. Roasted legumes like those of Bengal gram and peas are widely used in
India.
Cooking: Cooking destroys the enzyme inhibitors and thus improve the nutritional
quality of food pulses. Cooking also improves the palatability.
Fermentation: The processing of food pulses by fermentation increases their
digestibility, palatability and nutritive value. Fermentation process improves the
availability of essential amino acids and, thus, the nutritional quality of protein of
the blend. In general, the nutritive value of the legume based fermented foods has
been shown to be higher than their raw counterparts.
Pulse milling
Pulses are usually converted into Dhal by decutilating and splitting. Both dry and
wet milling processes are employed. By and large carborundum emery rollers are
used for dehusking and burr grinders for splitting. Decuticling is seldom complete
in single pass requiring multiple passes, each pass producing 1.5 to 2% fines
reducing recovery of dal.
Basic processes in dhal milling are cleaning, dehusking, splitting, separation and
bagging. Major variation is involved with dehusking process only. Dhals like
Arahar, urad, moong and lentil are difficult to dehusk as a result repeated
operations by dehusking rollers are required. Rewetting and drying is done to
loosen portions of husk sticking after repeated rolling. Linseed oil is used to impart
shine or better appeal to the milled dal.
The removal of the outer husk and splitting the grain into two equal halves is
known as milling of pulses. To facilitate dehusking and splitting of pulses alternate
wetting and drying method is used. In India trading milling methods produce
dehusked split pulses. Loosening of husk by conditioning is insufficient in
traditional methods. To obtain complete dehusking of the grains a large number of
abrasive force is applied in this case as a result high losses occur in the form of
brokens and powder. Yield of split & pulses in traditional mills are only 65 to 75%
due to the above losses compared to 82 to 85% potential yield.
Milling of Pulses
In India, there are two conventional pulses milling methods ; wet milling
method and dry milling method. The latter is more popular and used in
commercial mills.
Traditional dry milling method ('DHAL' MILLING)
There is no common processing method for all types of pulses. However, some
general operations of dry milling method such as cleaning and grading, rolling or
pitting, oiling, moistening, drying and milling have been described in subsequent
paragraphs.
Cleaning and grading
Pulses are cleaned from dust, chaff, grits, etc., and graded according to size by a
reel type or rotating sieve type cleaner.
Pitting
The clean pulses are passed through an emery roller machine. In this unit, husk is
cracked and scratched. This is to facilitate the subsequent oil penetration process
for the loosening of husk. The clearance between the emery roller and cage
(housing) gradually narrows from inlet to outlet. As the material is passed through
the narrowing clearance mainly cracking and scratching of husk takes place by
friction between pulses and emery. Some of the pulses are dehusked and split
during this operations which are then separated by sieving.
Pretreatments with oil
The scratched or pitted pulses are passed through a screw conveyor and mixed with
some edible oil like linseed oil (1.5 to 2.5 kg/tonne of pulses). Then they are kept
on the floor for about 12 hours for diffusion of the oil.
Conditioning of pulses
Conditioning of pulses is done by alternate wetting and drying. After sun drying
for a certain period, 3-5 per cent moisture is added to the pulse and tempered for
about eight flours and again dried in the sun. Addition of moisture to the pulses can
be accomplished by allowing water to drop from an overhead tank on the pulses
being passed through a screw conveyor. The whole process of alternate wetting
and drying is continued for two to four days until all pulses are sufficiently
conditioned. Pulses are finally dried to about 10 to 12 per cent moisture content.
Dehusking and Splitting
Emery rollers, known as Gota machine are used for the dehusking of conditioned
pulses About 50 per cent pulses are dehusked in a single operation (in one pass).
Dehusked pulses are split into two parts also, the husk is aspirated off and
dehusked, split pulses are separated by sieving. The tail pulses and unsplit
dehusked pulses are again conditioned and milled as above The whole process is
repeated two to three times until the remaining- pulses are dehusked and split.
Polishing
Polish is given to the dehusked and split pulses by treating them with a small
quantity of oil and / or water.
Commercial milling of pulses by traditional methods
The traditional milling of pulses is divided into two heads, namely, dry milling and
wet milling. But both the processes involved two basic steps : (i) Preconditioning
of pulses by alternate wetting and sun drying for loosening husk and (ii)
subsequent milling by dehusking and splitting of the grains into two cotyledons
followed by aspiration and size separation using suitable machines. 100 per cent-
dehusking and splitting of pulses are seldom achieved particularly in cases of
certain pulses like Red gram, black gram and green gram. Of them Red gram is the
most difficult pulses to dehusk and split. Only about 40 to 50 per cent Red gram
grains are dehusked and split in the first pass of preconditioning and milling. As
sun drying is practiced the traditional method is not only weather dependent but
also it requires a large drying yard to match with the milling capacity. As a result it
takes 3 to 7 days for complete processing of a batch of 20 to 30 tonnes of pulses
into dhals. Moreover milling losses are also quite high in the traditional method of
milling of pulses.
In general, simple reciprocating or rotary sieve cleaners are used for cleaning while
bucket elevators are used for elevating pulses.
Pitting or scratching of pulses is done in a roller machine. A worm mixer is used
for oiling as well as watering of the pitted pulses.
Blowers are used for aspiration of husk and powder from the products of the disc
sheller or roller machine. Split dhals are separated from the unhusked and husked
whole pulses with the help of sieve type separators.
Sieves are also employed for grading of dhals.
In general, the raw pulses may contain 2 to 5 per cent impurities (foreign
materials), some insect infested grains and extra moisture. Though the clean
pulses contain about 10-15 percent and 2-5 per cent germs, the yield of dhals
commercial dhal mills varies from 68-75 per cent. It may be noted that the
average potential yields of common dhals vary from 85 to 89 per cent. These
milling losses in the commercial pulses mills can be attributed lo small brokens
and fine powders found during scoring and simultaneous dehusking and splitting
operations.