Dehulling & Splitting Pulses

Seed Structure
• Pulses all have a similar structure, but differ in color, shape, size, and
thickness of the seed coat. Mature seeds have three major components:
the seed coat, the cotyledons, and the embryo.

• The seed coat, or hull accounts for 7–15% of the whole seed mass.
Cotyledons are about 85% of the seed mass, and the embryo constitutes
the remaining 1–4%.

• The external structures of the seed are the testa (i.e., seed coat), hilum,
micropyle, and raphe.

• The testa is the outer most part of the seed and covers almost all of the
seed surface. The hilum is an oval scar on the seed coat where the seed
was attached to the stalk. The micropyle is a small opening in the seed
coat next to the hilum. The raphe is a ridge on the side of the hilum
opposite the micropyle.
• When the seed coat is removed from grain, the remaining
part is the embryonic structure. The embryonic structure
consists of two cotyledons (or seed leaves) and a short axis
above and below them.

• The two cotyledons are not physically attached to each other

except at the axis and a weak protection provided by the
seed coat. Thus the seed is unusually vulnerable to
breakage.

• Table 2 shows the thickness of the seed coat (or hull) and
the force required to separate the two halves of the
cotyledons in field peas (Pisum satiyum, L.), measured in
newtons (N) using an Instron Universal Testing machine. The
required force is in the range 7.9–10.8 N.
• The seed coat breakages, measured using a tangential
abrasive dehulling device (TADD) (5), vary from 1.1% of the
seed mass to 6.1%, which demonstrates the large variability
in durability of the hull among varieties of peas.

• The outermost layer of the seed coat is the cuticle, and it can
be smooth or rough. Both the micropyle and hilum have
been related to the permeability of the testa and to water
absorption.
Khesari dal Horse gram (kulthi)
 Pulses

Edible fruits or seeds of pod bearing plant belonging to the

family of the legumes.
Consumed in the form of dehusked split pulses.
Legumes not only have dietry values but also improve soil
fertility
Lower blood cholesterol as increase faecal excretion of total
bile acids.
Gel forming polysaccharide.
 Names of some legumes
Common name Other name
Broad beans Faba beans

Haricot bean Rajmah bean

Lentils masoor
Bengal gram Chick pea
Black gram urad
Green gram Moong

Red gram Pigeon pea, arhar

Horse gram Kulthi
Cow pea Lobia
Peas Matar
 Nutritive value of the pulses (per 100 g)

Energy
Pulses give 340 calories per 100g which is almost
similar to cereal calorie value.

Protein
20 to 25 % protein.
Cheifely contains globulins albumins can also be
seen.
Deficient in methionine.
Red gram is deficient in tryptophan as well.
Other amino acids present are isoleucine, leucine,
phenylalanine, threonine and valine.
 Energy Moisture Protein Fat Mineral Carbohydrates Fibre Calcium Phosphorus Iron
Kcals g g g g g g mg mg mg
10 17 5 3 4 4 202 312 5
Bengal gram,
360
whole

10 21 6 3 1 1 56 331 5
Bengal gram,
372
dhal

11 24 1 3 1 1 154 385 4
Black gram,
347
dhal

Cow pea 323 13 24 1 3 3 4 77 414 9

10 25 1 3 1 1 60 433 3
Field bean, dry 347
10 24 1 3 4 4 124 326 4
Green gram,
334
whole

Green gram 10 24 1 3 1 1 75 405 4

348
dhal
12 22 0 3 5 5 287 311 7
Horse gram,
321
whole

10 28 1 2 57 2 90 317 6
Kherasi dhal 345

Lentil 343 12 25 1 2 59 1 69 293 7

11 24 1 3 56 4 202 230 9
Moth beans 330
73 7 0 1 16 4 20 139 1
Peas green 93

Peas dry 315 16 20 1 2 56 4 75 298 7

10 23 1 2 59 4 81 345 6
Peas roasted 340
12 23 1 3 61 5 260 410 5
Rajmah 346
8 43 19 4 21 4 240 690 10
Soyabean 432
 Biological value of some legume proteins

Legumes Biological values

Peanut 54.5

Pigeon pea 60

Soyabean 65

Green gram 70.4

Chick pea 79.5

Pea 81.7

Cow pea 89.2

 Carbohydrates
Contains 55-60% strach also contains soluble sugars,
fibres and unavailiable carbohydrates.

Unavailable sugars contains substaintial levels of

oligosaccharides of raffinose family ( raffinose and
stachiose) which produce flatulence .

Reduction in oligosaccharide is achieved by

fermentation cooking, soaking and cooking
 Lipids
Contain 1.5 % lipids on moisture free basis

Contain high amount of polyunsaturated fatty

acids such as linoleic acid, linolenic acid. Palmitic
oleic and stearic acid are also present.

Also undergo oxidative rancidity during storage

resulting in loss of protein solubility, off flavor
development and loss of nutritive quality.
 Minerals
Contains calcium, magnesium, zinc, iron, potassium
and phosphorus.
80% phosphorus as phytate phosphorus.

Vitamins
Excellent source of B complex particularly Thiamin,
Folic aid and Pantothenic aid.
Vitamin A and C are not present
 Antinutritional factor

Favism

Goitrogens

Hamemagglutinins

Saponins

Tannins
 Toxins
Cyanogenic Glycoside

Lathyrogens
 Milling

Milling of pulses means removal of outer husk and

splitting the grain into two equal halves
Premilling treatment

loosening the husk is achieved either by a wet or dry

method

Milling or dehulling
Pulse milling is practiced at different levels:
home-scale- pestle and mortar or hand-driven disk
mills (popularly known in India as chakki)
 cottage-scale- under-runner disk sheller, or hullers
 large-scale - emery-coated roller machines are used
mainly in large-scale operations
Home scale industry generally utilized wet method of milling

At commercial or large scale dry method of milling

Easy to mill Difficult to mill

Chickpea Red gram
Peas Green gram
Lentils Black gram
Beans
 Flow diagram of wet milling
Pulses

Cleaning → chaffs, dirts etc

Soaking

Mixing with red earth

Conditioning

Dehusking and splitting → (mixture of husk, small broken and powder)

Grading

Dehusked split pulses → grade 1 pulses

 Flow diagram of dry milling
Pulses

Cleaning → chaffs, dirts etc

Pitting → mixture of husk and brokens (feed)

Pretreatment with oil

Conditioning

Dehusking and splitting → (mixture of husk, small broken and powder)

Grading followed by polishing

Dehusked split pulses → grade 1 pulses

Wet milling dry milling
 UNIT OPERATIONS IN PULSE PROCESSING

• The sequence of operations in pulse processing is

1. Premilling treatment,
2. Dehusking or decortication, and
3. Splitting.

• In traditional operations, the dehulling is done either by the wet

or dry method.

• In the wet method, the pulse is soaked in water for several hours
before sun drying and milling.
• In the dry method, a small quantity of water or oil is applied
onto the grain and conditioning time is usually shorter.
Apparently, the wet method is no longer used in dal mills in
India .

• In the modern methods, high-temperature–short-time

heating is used for conditioning the grain for loosening the
husk. It is claimed that this treatment leads to 5–10% higher
dal yields.
 Cleaning and Grading

• Pulses must be cleaned during the process, because they may

be delivered containing up to 20% impurities.
• Foreign materials include pod walls, broken branches, soil,
cereals, oilseeds, weed seeds, diseased and deformed seeds,
and stones.
• Raw material is cleaned by removing dust, dirt, foreign
material, off-sized, immature, and infested grains. The
cleaned grain is graded into uniform sizes.
• Air and rotary screens with round holes are used for cleaning.
In rotary screens, however, the grain does not have equal
opportunity to come in contact with the sieve before reaching
the end of the separation zone, which leads to improper
grading.
• Normally, two types of cleaners are available:

– Rotary screen cleaners and

– Reciprocating screen cleaners.

The screens are used to remove the foreign materials on

the basis of size difference.

– The suction fan removes lighter material such as dust

particles.
The separation of splits from whole grain is done by the
screens.
• The rotary screen consists of four compartments of
different-sized screens fitted on 50-mm–diameter shaft.

• The screens clean different pulse crops.

• The machine is fitted on a sloped foundation (slope 50 mm

for 1 m length) and is operated at a low speed (18– 30 rpm)
for better performance.

• The body of a machine can be made of wood or iron (mild

steel), depending on the manufacturer or customer choice.
• Scalpers are used to remove large unwanted trash and fines.
The separation is done on reciprocating or rotating screens.

• The reciprocating flat screen cleaner has three screens and

one dust (suction) fan.

• The foreign material, including dirt, dust, and such, is

separated, and the pulse is graded for milling purposes.

• A stroke of 37–50 mm is provided for the reciprocating unit.

Details of size, capacity, and other specifications are shown
in Table 5.
 The functions of various cleaning and grading equipment

• Air-screen machines are used as scalpers for size separation

as well as weight separation. The material is aspirated to
remove light materials, then passed over screens to remove
large materials as overs. The unders are passed on a second
screen to separate fines from desired size seeds.
• Disk separators consist of series of cast iron disks mounted on
a shaft revolving at a very precise speed relative to disk
diameter within a cylindrical housing. The disks have precise
undercut pockets with size and shape variations which allow
the smaller seeds to be lifted and to reject larger seeds.
• Indent cylinders are machines of choice for length separation.
They are almost horizontal rotating cylinders lined with
hemispherical depressions. Short seeds are picked up in the
indent and lifted up and thrown into an auger to be carried
out of the rotating cylinder.

• Width and thickness separators are typically rotating,

cylindrical, perforated shells. Larger seeds will not pass
through and discharge from the end of the cylinder.
Gravity separators

• It separate seeds based on a combination of shape, size,

specific gravity, and surface characteristics.

• The seed mixture is fed onto an oscillating deck with a

carefully controlled air movement to fluidize the material.

• The mixture is stratified—lighter up and heavier down; the

seed layers along the deck in different directions toward
discharge ends.
• Color sorters have proved to be very effective but need
considerable adjustment, capital investment, and are slow,
although it is expected that improvements in speed will be
made.
 Seed Conditioning to Promote Dehulling

• Conditioning is a general term applied to heating, cooling,

wetting, drying, or any combination of these processes.

• The effects of conditioning on the seed could be to toughen

the hull (bran), loosen the bond between the hull and the
cotyledon, crack the seed coat, and harden the cotyledon to
resist damage.

• Heat treatment of moistened grains, or in some dry grains,

makes the hull easier to remove as it becomes brittle and
cracks.
• The cotyledons tend to shrink more than the hull during this
process, resulting in the hull being loosened from the
cotyledon.

• Addition of moisture softens the grains and make them

susceptible to scouring; whereas drying hardens the grains
and increases their resistance to scouring.
Dehulling efficiencies were best for the following conditions:

• Smaller-sized seed, shortest drying time, least immersion

time, and longer tempering time.

• The drying temperature did not affect dehulling efficiency.

• The increased seed moisture content (longer immersion) had

a negative correlation with the dehulling efficiency.
Pitting

• Whole pulses are passed through abrasive roller machine for

scratching the seed coat to facilitate the entry of oil and water in
the grain during premilling treatment. Some seeds (2–5%) are
dehusked during pitting.
 Pitting
Cylindrical (mounted inclined) 75 X 25 cm to 90 X 35 cm
Tapered (horizontal) 17 x 20 X 60 cm to 35 X 45 X 90 cm

Angular gap between roller & wire mesh screen 2 to 4 cm

Grit size depends upon type and size of pulse used.

Varies from 14 to 16 to 36 to 40
Rough emery 14 to 16 mesh for pigeon pea
Fine emery 36 to 40 mesh for pitting almost all pulses

Pitting generally done at low peripheral speed 610-670 m/min

For pigeon pea high peripheral speed 850-975m/min required.
Oil and Water Treatment

• Edible oil treatment is used to loosen the husk of difficult-to-

mill pulses. The quantity of oil used varies from mill to mill.

• Water treatment, which varies with crop, is used to expand

seeds, which helps in loosening the husk by contraction of
cotyledons during drying.

• Some dal millers apply water and oil simultaneously. This is

done to reduce the process time.
 Pretreatment with oil

• Screw or paddle type conveyor used for mixing edible

oil (1.5 to 2.5 kg/tonne of pulses).
• Screw rotated at 50-70 rpm to achieve proper mixing
• The length and width of Conveyors range between
15000 to 2500 and 200 – 300 mm resp.

Elevators
• bucket elevators that are made of either wood or steel
are normally employed
• Capacity, number and height depend upon type of mill
 Conditioning
• 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 hours 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.
 Conditioning
Sun drying

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.

Batch type drier with 1-3 tonnes holding capacity can be

used.
• Addition of large quantities of water during processing and
nonremoval of the entire quantity during drying adds about
3–5% to the weight of the product and reduces the storage
life of dal.
• Large variations in quantity of water added lead to increased
energy costs for moisture removal and process time. This also
reduces dal recovery.

• Treated grains are heaped and covered with gunny bags and
left for 12–18 h.
• This helps penetration of the oil and water into the cotyledons
after mixing and grain temperature equilibration after drying
in the sun.
• Some wooden or cement tanks are used for storing the
treated grains.
 Kernel Temperature and Moisture Content

• Seed coat breakage was most affected by seed moisture content,

followed by temperature and cultivar.
• At all temperature levels, seed coat breakage increased linearly
with decreasing moisture content.

• This may be due to changes in either tissue elasticity or the

binding between the inner seed coat surface of the cotyledon.

• When the tissues begin to lose moisture, there is an increase in

brittleness caused either by an increase in crystallization or by a
change in cell orientation.
 Drying

• Normally, pulses are sun-dried as part of premilling treatment and

for the loosening of husk. The size of a drying yard has no
generalized correlation with the capacity of a mill, and drying time
ranges between 3 and 8 days.

• Some times thick-layer, sun-drying is followed, which results in

non uniform drying and breakage during milling. This is a crucial
part in premilling treatment and needs consideration.

• The premilling treatment, as such, varies from miller to miller and

thereby results in repeated exposure of grains to milling
machinery, adds to breakage and lowers the dal recovery.
 Sun Drying

• Normally, sun drying is practiced in drying yards or roof tops for

drying.
• Grains are spread in a thin layer (3–10 cm) and turned frequently
with a rake for even drying.
• Some dal millers prefer thick layers (up to 15 cm) of grains in the
drying yard for reasons of quality improvement. The drying period
for grains varies from 1 to 5 days depending on weather conditions,
thickness of layer, and pulse crop.
• Most of the dal millers employ sun-drying in open drying yards: 0–1
m2/kg of pulse is sometimes used as a rule of thumb.
• Some millers avoid drying or reduce drying time and mill the pulses
after tempering for 8–12 h. This results in heavy breakage during
milling.
• Some of the dal mills are equipped with dryers, but these are
preferably used in the rainy season or in situations of unfavorable
weather conditions.
Losses in Conditioning
• Some pulses such as green gram and pigeon pea have a tendency to split
before they are completely dehusked. This leads to repeated exposure of
grain to milling machinery for complete husk removal, and leads to high
breakage.

• Insufficient premilling treatment also contributes to this problem.

Another important aspect in pulse milling that leads to breakage is
problems in separation of gota and whole grains. The unprocessed lot
consisting of a mixture of gota and whole grains at the end of a pass is
reprocessed for dal making.

• Since commercial equipment available for gota separation is not

effective owing to the same size of grain and gota, the gota in the
mixture is again exposed to a premilling treatment, which renders it
weak and leads to a high percentage of brokens during exposure to the
dehusking machine.
 Dehusking of Pulses

• Dehusking or shelling of pulses is a preparatory operation for

splitting.
• Dehusking is preferably achieved by subjecting the grains to
abrasive force and splitting by attrition or impact.

• Generally, three to nine passes are required for milling

various pulses, and this depends on the type of pulse crop,
premilling treatment given, processing technique adopted,
grain size, and variety.

• Splitting during milling is normally a disadvantage, as the

splits scour at the edges causing powder loss. One of the
causes of higher loss is more surface area when grain is split.
• Carborundum emery-coated rollers are used for dehusking
different pulses.
• The rollers are of two types: cylindrical and tapered.
• The foundation is horizontal for the tapered rollers, whereas
it is sloped for the cylindrical roller. Normally, a slope of 15
cm/m infoundation for the entire length of the machine is
recommended.
• The body of a roller is made of steel on which the mixture of
Carborundum emery, chemical cement, and salt is applied and
dried to make a uniform, circular abrasive surface.

• The granular size of emery varies from crop to crop and is

recommended by manufacturers.

• The inlet and outlet of the roller can be adjusted for regulation of
flow and retention time.

• These rollers are available in different sizes and are specified as 23

53.5 4 cm, where 23 is the diameter of the roller, 53.5 is its
length, and 4 is the diameter of the shaft.
 TADD (Tangential Abrasive Dehulling Device)

• This machine was developed at the Prairie Regional Laboratory

(PRL) of the National Research Council of Canada in Saskatoon and
is used for testing the dehulling properties of grains.

• A resinoid, steel cutoff disk of 250-mm diameter and 3.12-mm

thickness is mounted directly on a 0.0375-kW, 1725-rpm electric
motor, which is supported on a stand.

• An aluminum head plate holds eight stainless steel sample cups

(46.88-mm diameter and 17.19-mm deep) above the resinoid disk.
The cups open at both ends, are mounted vertically with their
centers equally spaced around a 184.37- mm–diameter circle.
• A rubber-faced aluminum cover plate closes the tops of the
cups when the machine is in operation. With the machine
assembled, the threaded head plate supports are adujusted
so that the lower edges of the cups are lightly ground by the
resonoid disk to assure minimum clearance between the
cups and disk.

• In operation, weighed samples of grain are placed in the cup,

the cover plate fastened in position, and the resonoid disk
rotated under the cups at 1725 rpm for a specified time. The
abraded samples are then removed from the sample cups
with the vaccum sample collector.
 CIAE Design
• An abrasive emery roller cylinder mill to dehusk and split pulses to make
dal (Fig. 6) was developed at the Pulse Processing Laboratory of the
Central Institute of Agricultural Engineering, Bhopal, India (16).

• The mill consists of 250-mm–diameter cylinder coated with emery paste

and an outer working layer of Carborundum.

• The clearance between the outer screen cage and inner abrasive roller
was maintained throughout at 10 mm. The performance of the mill was
evaluated evaluated for different pulses and at different speeds.

• The maximum milling efficiency was obtained at 850–900 rpm (13.5- to

14-m/s roller surface speed). Dal recovery was 74–75%.
 CFTRI Design
• A minimill dehuller with a capacity of 150–200 kg/h has been developed
by CFTRI, Mysore, India.
• The mill consists of an emery-coated metal cone fixed to a vertical shaft
and rotating inside a fixed conical wire mesh screen.
• A screw at the base of the shaft can raise or lower the emery-coated
cone.
• The screen and the cone are concentric, and their clearance is about the
diameter of a grain.
• The grain stream is regulated into the machine such that it does not jam
the machine.
• A dust cover, with a hopper at the top, envelopes the screen. Another
hopper collects the mill stream.
• The seed must be preconditioned before dehulling.
• Chickpeas are dehulled in this unit giving 78–81% dal yield; 1–2%
brokens; and 17–20% husks and powder (21).
 Husk Separation and Grading
• Husks are separated by aspiration and sold as animal feed.

• Some fine brokens are present in the husk and, if separated, can make
available an extra quantity for human consumption.
•
• Grading adds to the quality of product by separating the dehusked
unsplit grains (gota), whole grains, brokens, and dal in two grades.

• However, problems in separation of gota and whole grains owing to their

same size and shape, leads to repeated exposure of grains to the
machine and breakage during milling.
• A new method of separating whole and decorticated grain based on their
bouncing properties has been reported. A succession of four hard
surfaces is used to bounce the whole seed and the decorticated seed. A
61% efficiency of separation was established in the laboratory trials for
pigeon peas.
• The mixture of brokens and husk is separated from the
dehusked pulses and splits by using a suction fan or blower
and the mixture is used as animal feed.

• To separate the brokens for human consumption, the use of

a specific gravity separator is advocated. This machine gives
separation of about 5% brokens available in the mixture. The
machine is supplied with three, four, and five fans, with a
capacity ranging from 635 to 4500 kg/h.
 Polishing

• Whole pulses, such as pea, black gram, green gram, and splits (dal),
are polished for valueadding. Some consumers prefer unpolished
dal, whereas others need dal with attractive color (polished dal).
• Accordingly, dal is polished in different ways such as nylon polish,
oil–water polish, color polish, and so on.

Removal of Powder and Dust

• The cylindrical roller mounted with hard rubber, leather, or emery
cone polisher, and roller mounted with brushes are used for the
purpose.
• The powder particles are removed by the rubbing action. Speed and
sizes of these types of polisher are similar to those of the cylindrical
dehusking roller.
• Another type of machinery provided for this purpose is a set
of screw conveyors arranged in battery for repeated rubbings.
• The flights and shaft are covered with nylon rope or velvet
cloth.
• The speed of each screw conveyor varies. The repeated
rubbing adds to the luster of the dal, which makes it more
attractive.
• These polishers are commonly known as nylon polisher or
velvet polisher, depending on the material used, and are
available in a set of 2, 3, 4, or 5 screw conveyors.
Oil and Water Polish
• The screw conveyor similar to one supplied for oil and water mixing
is provided for oil and water polish. The speed, size, and capacity,
are similar to those of the oil and water mixing machine.

Splitting of Pulses
• Splitting of dehusked pulses and pulse seeds is one of the major
operations in the dal mill.
• It is aimed at the production of perfect splits, with edges and
without breakage.
• Different types of equipment are employed for the purpose: roller
machine, under runner disk sheller, attrition mill (Chakki), elevator
and hard surface, and impact sheller.
 Roller Machine

• The machine similar to one used for dehusking is used for

splitting of different pulses.
• A course emery coating is required for the splitter roller (Table
7). The rollers are used for splitting green gram, pigeon pea,
lentil, and others.
• Roller machines are based on the principle of abrasion.
• Revolutions and diameter of roller (peripheral speed),
roughness of surface, length of roller (hold-up time), abrasion
force, abrasion pressure, and clearance between the roller
and the lower sieve are some of the factors that determine
the extent of dehusking and scouring on this machine.
 Under Runner Disk Sheller
• The machine is simple in construction. It has two horizontal disks
with emery coating of 12-mm thickness. The upper disk is
stationary; the lower one rotates to cause splitting of dehusked
pulse (gota).
• It is used for splitting dehusked black gram, chickpea, lentil, pigeon
pea, and soybean. The capacity of a machine depends on its size
and speed.
• The sheller machines cause breakage as high as 30–40%
particularly if the grains are not thoroughly size-graded. Revolutions
of the disks, peripheral speed as determined by the speed of
rotation and diameter, roughness of contact surfaces and their
parallelism, the distance and duration the grains roll (under
pressure) between the revolving disks play important roles in
splitting or breakage in these machines.
Attrition Mill
• Attrition mills of vertically or horizontally rotating stone disks or
emery disks are also used to split pulses.

Elevator and Hard Surface

• This combination is used by some dal millers, and it is believed that
breakage is lower. Dehusked pulses are dropped from a height of
about 10–15 ft on a hard surface and splits are obtained. This type
of arrangement is normally used only for pigeon peas.
 Dal Grading and Gota Separation Machinery

• The machinery similar to the one used for cleaning and grading of pulses is
used for gota separation and dal grading.
• A three- and four-compartment rotary sieve is used for gota separation
and dal grading, respectively. Some manufacturers supply a reciprocating-
type screen with 37- to 50-mm–stroke length for gota separation and dal
grading.
• A combination of rotary screen cleaner for raw material cleaning and
reciprocating screens for gota separation and dal grading is also employed
by some millers.
• The size of perforations vary depending on the type of grain to be
processed.
• These units are built in a wooden or mild steel frame and are used for the
separation of gota, splits, and brokens.
Pulse Conditioning and Dehusking for Modern Mills

A conditioning unit consists of two sets of tempering bins, two

pulse heating units, each having separate motorized blowers,
air heat exchangers, grain-heating chambers, and feed
hoppers. The temperature is controlled thermostatically. This
entire unit is used for conditioning grain to loosen the husk.
Gota Conditioning and Splitting Unit for Modern Mills

A gota-conditioning unit consists of a motorized blower, air

heat-exchanger, gota heating chamber, and thermostatic
temperature control arrangement for gota heating and one
blower for the aeration chamber, with a mechanized delivery
outlet for aerating gota with moist air. The unit provides the
conditions necessary for treating the gota for loosening the
binding of the cotyledons and minimizing the breakage during
splitting.
Flowchart for processing of pulses.
Motorized stone grinders (chakkies): (a) horizontal (b) vertical.
Huller Horizontal cone polisher.
Under-runner disk sheller
Pigeon Pea
• This pulse poses the greatest difficulty in milling because the husk adhers
tightly to the cotyledons.
• Generally, only the dry method is followed throughout the Indian
subcontinent for milling of this pulse.
• Cleaned and size-graded grains are pitted, smeared with varying amounts
(0.2–0.5%) of oil (any edible oil), tempered for about 12–24 h, sun-dried
for 1–3 days, followed by spraying with water (2–6%), thoroughly mixed,
heaped overnight followed by drying, and then passed through the rollers
for dehusking.
• This type of operation is repeated three or four times.
• After each dehusking operation, the husk, powder, and brokens are
separated from dehusked split pulse (dhal).
• Dehusked splits obtained in this operation are considered as ‘second
grade’ because their edges are not sharp and are usually rounded-off by
scouring.
• The mixture of dehusked and unhusked grains obtained during
processing (known as Kappi) is again mixed with water, as described
earlier, equilibrated, and sun-dried.
• The sun-dried grains are either passed through the roller machine
or split in a horizontal or vertical grinder or by using an impact-type
machine.
• The dehusked splits thus obtained are considered as a ‘‘first grade,’’
because they would not have any chipped edges and would have a
better consumer appeal.
• Quite often both first- and second-grade dehusked splits are mixed
and marketed.
• The yield varies from 70 to 75% depending on the variety and the
method followed.
• In large-scale mills, sun-drying is being replaced gradually with
batch-type bin driers, as a result of which they are able to continue
work throughout the year.
Chickpea

• The chickpea is comparatively easy to mill.

• The cleaned and size-graded grains are pitted in smooth rollers at
low peripheral speed.
• After pitting, the grains are mixed with about 5–10% water in a
screw–conveyer-type mixer and heaped for a few hours to allow
the water to seep in.
• The wetted grains are sun-dried for 1 or 2 days.
• The dried pulse is then passed through either a horizontal or
vertical stone–emery grinder, where dehusking and splitting takes
place simultaneously.
• The dehusked splits are separated from the husk and brokens with
an appropriate aspirator and sifter;
• the remaining unhusked grains are dehulled by repeating the
foregoing operation until all the grains are dehulled.
Black Gram

• The cleaned and size-graded grains are pitted using emery rollers in two or
three passes, so that complete scarification is effected.
• After each operation the husk and powder are separated.
• The pitted grains are then mixed with about 0.5% oil and heaped
overnight for absorption. The grains are then sun-dried for 2 days.
• In some mills mechanical dryers are used. After drying, the grains are
given a spray of water (2–5%), equilibrated, and passed through the rollers
twice for dehusking.
• The splits obtained are termed second-grade dhal.
• The dehusked whole grains are either marketed as such at certain places
in India or passed through a Burr mill for splitting.
• These splits are considered first-grade.
• The splits are ‘‘polished’’ with soapstone powder at the final stages. This is
believed to give luster and enhance their market value.
Green Gram

• The husk of green gram is thin, soft, and slippery.

• Although the husk tightly adhers to the grain surface, the two
cotyledons are loosely attached and separate out easily.
• Hence, splitting occurs even before good dehusking can be
effected. During the dehusking operation, there is also
scouring of the cotyledons, resulting in large losses in the
form of brokens and powder.
• The method generally followed is pitting, oiling (0.2–0.5%),
and sun-drying,
• After drying, the grains are given a spray of water (2–5%),
equilibrated, and followed by dehulling and splitting in roller
machines.
Peas and Lentil

• The milling of these pulses is fairly easy as found for chickpea.

• General practice involves initial scouring, application of water,
heaping, and sun-drying, followed by dehusking and splitting
in roller machines.
• After separating the splits, unhusked grains are treated again
for a second time as in the first pass, and the process is
repeated until all grains are dehusked and split.