METHODS OF PULSE MILLING WET AND DRY METHOD, DOMESTIC AND

COMMERCIAL MILLING

15.1 Introduction
Pulses are defined as dried edible seeds of cultivated legumes. Pulses occupy important place
in human diet. They serve as major sources of dietary protein and energy. The production of
pulses in India was 13.19 million tones in 2001-02, which was 27% of the Worlds
production. Bengal gram/Chick pea (chana), pigeon pea (tur/arhar), cow pea (lobia), black
gram (urad), green gram (moong), lentils (masur), peas (matar) are some of the major pulses
grown in India.
Pulses are consumed in its dehusked and split form which is termed as dal. Pulse milling (dal
milling) is accomplished in three major steps namely: loosening of husk, dehusking and
splitting of pulses. Pulses are generally consumed in the form of Dal. Traditional methods for
processing of pulses were labour intensive, time consuming and incurred losses. Modern
technologies for processing of pulses have replaced old age methods and thus avoid losses
and saves time. Processing of pulses involves two basic steps - (i) seed coat/husk loosening
and its removal and (ii) conversion of seed grain into splits and grinding into flour depending
upon its end-use. Various methods are employed for pulse/dal milling. Pulses undergo some
basic unit operations during pulse milling such as cleaning and grading, drying, loosening of
husk, dehusking, splitting and polishing.
15.2 Methods of Pulse Milling
15.2.1 Wet milling of pulses
Wet method of pulse processing (Fig. 15.1) involves cleaning to remove dust, dirt, chaff,
stone pieces, immature grains and other seeds. The easy to dehusk pulses are then soaked into
water for a period of 2 - 8 hrs whereas difficult to dehusk type of pulses (pigeonpea, black
gram, green gram) are often treated with red earth. The pulses are subsequently dried and
then subjected to dehusking and splitting to obtain Dal.
15.2.2 Dry method of pulse milling
In case of dry method of pulse milling (Fig. 15.2), the pulses after cleaning are fed into roller
dehusker where a scratch, dent and crack is formed on the outer seed coat. Pitted pulses are
then stored for day to 3 days after applying oil on the surface. Generally 150 - 250 gm oil per

100 kg pulses is applied. The oil diffuses between husk and cotyledon and thus facilitates
loosening of the husk. Water treatment (2.5 - 3.5 kg water/100 kg pulses for overnight period)
helps in further loosening of the husk. Then the pulses are subjected to drying and cooling.
Now, the dried pulses are dehusked and splited to obtain dal.

Fig. 15.1 Wet milling of pulses

Fig. 15.2 Dry milling of pulses

15.3 Home Scale Milling of Pulses

The home scale method of processing of pulses involves pounding of pulses into mortar and
pestle. Home scale method of pulse milling is different for different pulses and varies from
region to region. In this method, the husk is loosen either by wet or dry method; treating the
pulses with water and/or oil. The pulses are then generally stored overnight and the next day
they are sun dried. The removal of husk is then carried out in pestle and mortar or by a hand
operated stone mill. The husk then is separated by winnowing.
15.4 Commercial Scale Milling of Pulses
15.4.1 Cleaning and Grading
Pulses received at the mill needs to be cleaned and size graded for yielding good quality dal
with higher recovery. Even during dehusking operation, pulses are subjected to sieving to
separate out husk, brokens, splits, gota (dehusked pulse) and whole (unhusked) pulses.
Usually two, types of cleaners are used: reciprocating air-screen cleaners and reel screen
cleaners.
In reciprocating air screen cleaners air is blown through two screens (sieves) which separate
out lighter material such as dust, stalk, dried leaves, husk etc. The upper screen has bigger
perforations while second screen has smaller perforations. The reel screen cleaners consist of
2-4 cylindrical compartments. The frame of the machine is made of wooden or mild steel
sheet. In these compartments different size perforation screens are fitted on a 5-7.5 mm
diameter shaft. The machine is fitted at an inclination of 2-3. The cylindrical screen drum
rotates at 5-35 rpm.
15.4.2 Drying of Pulses
Drying of pulses is necessary to ensure safe storage before milling as pulses received at mill
have generally higher moisture content. After steeping of pulses for loosening of husk, it is
also necessary to dry pulses. During splitting operation too, it is very much essential to dry
the pulses to separate cotyledons. Sun drying of pulses is economical option for drying of
pulses. The sun drying is done for 1-6 days as per the requirement. The pulses are spread over
floor/roof in 5 to 7.5 cm thick layer which are intermittently stirred manually with the help of
rakes or turning by foot. At night, the drying pulses are collected in heaps and covered with
canvass sheet to preserve the heat. Mechanically heated air dryers, either batch type or
continuous flow type are also used by the millers. The temperature of heated air for drying
varies from 60 to 120C.

15.4.3 Loosening of Husk

This is very important step in pulses milling as it decides the total recovery and quality of
milled dal. Loosening of husk is accomplished in two different ways: wet method and dry
method.
15.4.3.1 Wet Method
Cleaned and graded pulses are soaked in water for 4-12 hours for steeping, mixed with red
earth for 12-16 hours and then sun dried to keep the moisture content about 10-12 %. During
steeping the husk becomes loose and thus facilitates easy dehusking and splitting. Yield is
also increased due to lesser breakage. But cooking time increases when the dal is obtained by
this method. Red earth is used as it impart a good yellow colour to the end product and also
helps to remove small patches of adhering husk due to its mild abrasive quality.
15.4.3.2 Dry method
In this method, husk is loosened by sequence of operations such as: oil smearing, water
application, tempering and sun-drying. Cleaned and graded pulses are passed through roller
dehusker in which scratches, cracks and dents are created on hard seed coat of pulses. This is
known as pitting of pulses. The pitted pulse grains are then passed through the sieve cleaner
to separate out the splits, husk and powder and later smeared with oil (100-500 gram per
quintal of pulses) either manually or with auger mixer and stored for 1-5 days. During this
tempering period oil diffuses in between the husk and cotyledons and weakens the bond and
thus facilitates loosening of the adhering husk. At the end of storage period, water is applied
to the grains (1-5 kg/q) and stored for further 12-14 h (overnight) and at last sun-dried for 1-3
days before subjecting to milling.
15.4.4 Dehusking
Roller dehuskers coated with carborandum are used to dehusk the pulses. Two types of rollers
viz. cylindrical and tapered are available for dehusking. Tapered rollers are placed
horizontally and the diameter of roller increase from feeding side to discharge side. The
difference in diameter helps to gradually increase the pressure on pulse grains and thus helps
in gradual dehusking. The cylindrical rollers are installed at an angle of 10-15 which
enables forward movement of pulse grains inside the machine. Annular gap between rollers
varies depending upon the type of pulses being dehusked. Inlet and outlet of the roller
machine can be adjusted for regulation of grain flow and retention time respectively. Small

dal mills use under run disc shellers or burr mills for dehusking operation in place of Roller
mills.
Conditioned pulse grains subjected to mild abrasion inside the roller machine, removes 1025% of husk in one pass. Shelled husk, cotyledon powder, brokens and splits are separated
out by Air-screen cleaners after passing the grain lot once or twice through the roller
machine. Depending upon adherence of husk to grain, the pulse grains are passed through
mill for two to eight times.
For hard-to-dehusk pulses (arhar, moong, urad), the recovery is between 70-75% while for
easy-to-dehusk pulses (bengal gram, lentil, kesari and peas), it varies in between 78-85%.
15.4.5 Splitting
Splitting operation involves loosening the bond between the cotyledons and splitting. For
cotyledons loosening, water at the rate of 1-5 kg/quintal is applied to dehusked pulse grain
(gota) and is stored for 2-12 hours and later sun-dried for 4-8 hours. For splitting, machines
like under-run-disc sheller (URD), impact machine (Phatphatia), roller mill, and hitting the
gota against the metal sheet at discharge side of bucket elevator are used. In this operation the
embryo attached to two cotyledons breaks away, thereby, causing a loss in dal recovery by
1.5 to 2%.
15.4.6 Polishing
In this operation dal is imparted with a glazing appearance to improve its consumers
acceptance and market value. Depending upon the need, different materials like water, oil,
soapstone powder and selkhari powder are applied to dal surface. Sometimes removal of
sticking powder from dal surface is considered sufficient to improve its surface glaze.
15.4.6.1 Removal of powder/dust
Cylindrical rollers mounted with the rubber mats, leather strips, emery rollers are used for the
purpose. The dust particles sticking to dal surface are removed by gentle rubbing action on
the roller surface.
15.4.6.2 Water polish
This is used for hard-to-dehusk pulses. In this method 1-1.5 kg of water per quintal of dal is
applied while passing it through polisher.
15.4.6.3 Buff polish

In this method 2-2.5 kg of water and 200-250g of oil per quintal of dal is applied while
passing it through polisher.
15.4.6.4 Nylon polish
Soapstone powder or selkhari powder (1-1.5kg/q) is applied to the surface along with water
(1-1.5 kg/q) while passing through the polisher. Screw conveyors battery for repeated
rubbings is used. The flights and shafts are covered with nylon rope to impart gentle rubbing.
15.4.6.5 Teliya dal
2.5 to 3.0 kg of castor oil is mixed per quintal of arhar dal to make it look glossy. The storage
life of teliya dal is short.