Pulse Milling
Milling of pulses consists of 2 steps: loosening the husk and its removal followed by splitting into dhal. Loosening of the husk referred to as "pre-milling treatment" is normally achieved by wet or dry method, which involves intermittent sun-drying after the application of oil and water. Dehusking or dehulling or milling and splitting are done in chakkies or power driven machines. Milling is usually done by two methods:
(a) Wet process:
The wet process has been commonly used with pigeon pea or red gram, as the skin in this grain is difficult to be removed. The process consists of the following steps: (i) soaking the grain in water overnight, (ii) smearing the soaked grain with red earth mixed with water and keeping the grain moist as a heap by sprinkling water for 16-24 hours, (iii) drying the grain in sun, and (iv) dehusking the grain using granite or wooden hullers.
(b) Dry process after conditioning skin with water or oil:
(i) Dry process after conditioning skin with water-chickpea, lentils, lathyrus, pea and dried peas.
(ii) Dry process after conditioning skin with oil-pigeon pea or red gram, black gram and green gram
In the first process, the grains are cleaned and after an initial scouring or pitting operation in roller mills, they are sprayed with water 5-10% by weight of the grain and kept in a closed vessel for the water to be fully absorbed by the skin. The material is then dried in the sun. Similarly, in the second process, the cleaned and pitted grains are treated with a vegetable oil (0.2 to 0.5%). The grains are dried in the sun and then conditioned by spraying water (about 4-5%). The conditioned grains are again dried in the sun.
In both the pre-milling treatments, adherence of the husk to the cotyledon weakens and consequently, its removal becomes easy.
The loosened seed coat of the pretreated pulses is then removed in the subsequent operation of milling. For this purpose, different machines are used depending on the types of pulses and scale of operation. Pulse milling is practiced at different levels, viz, (a) home scale, (b) cottage scale, and (c) large scale level and machines like pestle and mortar, hand-driven chakki are used in home-scale and roller mill in cottage and large-scale operation. There is much loss due to powdering and /or breakage. This process is dependent on climatic conditions, laborious and does not give more than 70% of dehusked and split grains although higher yields are possible.