|Machinery and capital|
|Raw material and working capital|
|Size capacity and out turn|
|Added value and profitability|
|Market for final product|
|Processing of pulses
|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. There are about 4000 pulses mills (Dal mills) in India with varying capacity of
pulse mills ranging from 10 to 12 tonnes per day.
Pulses are usually converted into Dal 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 dal milling are cleaning, dehusking, splitting, separation and bagging. Major variation is involved with dehusking process only. Dals 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.
Procedure for pulse milling:
There are two types of conventional pulse milling methods in India. Wet milling and dry milling method. Flow diagram of wet milling is given below:
Dry milling of Pulses :
For all types of pulses there is no common processing method. However, some general operations of dry milling method such as cleaning and grading, rolling or splitting, soiling and moistening, drying and milling are considered.
Cleaning of pulses from dust, chaff, dirt, grits, etc. and grading according to size is performed by a reel type or rotative screen type cleaner.
An emery roller machine is used to obtain cracking and scratching of clean pulses passing through it. For loosening the husk to facilitate the subsequent oil penetration this is required. 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 dehusked and split which are separated by sieving.
A screw conveyor allows to pass the scratched or pitted material through it and mixing of some edible oil like linseed oil is completed. The linseed oil is used at the rate of 1.5 to 2.5 kg/tonne of pulses. These are kept on floors for about 12 hours to diffuse the oil.
Pulses are conditioned by alternate wetting and drying. Moisture (3.5%) is added to the pulses after sun drying for a certain period and tempering is done for about eight hours. The grain is dried in the sun again. By allowing water to drop from an overhead tank on the pulses which are passed through the screw conveyor addition of moisture to the pulses are achieved. Until all pulses are sufficiently conditioned the whole process of alternate wetting and drying is continued for two to four days. Pulses are finally dried to about 10 to 12% moisture content.
For dehusking of conditioned pulses emery rollers called as Gota machine are used. In one pass or single operation about 50% of pulses are dehusked. Dehusked pulses are split into two parts. Dehusked split pulses are separated by sieving and the husk is aspirated off. Unsplit dehusked pulses and tail pulses are again dehusked and milled in a similar way. Till the running pulses are dehusked and split of the whole process is repeated tow or three times.
Polishing is completely by treating dehusked and split pulses with a small quantity of oil and/or water.
CFTRI modern method of pulses milling
Steps involved in CFTRI method of processing are
To remove all impurities from pulses and separate them according to size cleaning is done in rotary seed cleaners.
LSU type dryer is used to condition the clean pulses into two passes using hot air at about 1000C for a certain period of time. Hot pulses are tempered after each pass in the tempering bins for about six hours. In loosening husk pre conditioning of pulses helps significantly.
Pearler or dehusker are used to dehusk the preconditioned pulses in a single operation where almost all pulses are dehusked. Separation of dehusked whole pulses (gota) from split pulses and mixture of husk, brokens etc. (chunni-Bhushi) is done which are received in a screw conveyor where water is added at a controlled rate. The moistened gota are collected on the floor and allowed to remain as such for about half an hour.
Lumps of varying sizes are formed by some of the moistened gota. A lump breaker is used where these lumps are fed for further breaking.
The gota, after lump breaking is conveyed to LSU type dryer where it is exposed to hot air for a few hours. For splitting the gota is dried to the proper moisture level. In emery roller the hot conditioned and dried dehusked whole pulses are split. In one pass all of them are not split. Grading of mixture is done to get grade I pulses, dehusked whole pulses and small brokens. For subsequent splitting the unsplit dehusked pulses are again fed to the conditioner.
|Machinery for pulses
Pulses are processed in India for converting the raw material into variety of products. Machinery is available for production of dal dehusked splits, roasted and pulse flour and polished pulses. Selection of machine depends upon the type of pulses crop to be processed and the product desired.
Hand operated machines
Power operated machines: