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.