Millets are cultivated predominantly as rain fed crops. They are known to be fairly hardy and can survive long dry spells and fare reasonably well even when there is too much rain. Their hardiness allows for farmers to cultivate these crops with minimum inputs and efforts. Small millet crops do not require the field to be leveled, or sown with uniform spacing, or fertigated, or weeded. These would improve the yield and the quality of the harvest, but they are not critical. As most farmers cultivating these crops have limited means, these on-farm tasks are very often skipped.
Even in farms that better cultivation practices are followed, the adaptations of small millet crops have resulted in staggered flowering, grain formation and ripening within a plant, and within a field. So when harvested, it is not unusual to find grains of various sizes and maturity. Grading allows us to remove the smaller, not full formed, and immature grains. It also allows us to separate out seed quality grains from within the lot providing a selection and thereby improving the seed quality.
There are two grain characteristics that are used to grade grains – size and density. We use an eccentric or vibrating grader to achieve size grading and a destoner to achieve density grading. As one would expect, grading and cleaning go hand in hand – as we remove the extremes of the size and density distribution, we remove material other than grains (also referred to sometimes as MOTG).
- The smallest of the grains are typically removed with sand and go back to the farms to enrich the soil.
- Grains that are slightly bigger, but are mostly husk with very little endosperm inside will get used as a cattle feed.
- Grains that are even bigger, but in which the endosperm hasn’t formed fully will get used as bird (chicken) feed.
- Grains that are bigger and heavier than these, in which the endosperm is fully formed will be taken for further processing with the resulting product(s) being used for human consumption.
- The top 10% biggest and heaviest grains are separated out from the lot and stored appropriately for use as seeds.
The tighter the distribution (in both size and density), the better will be the output from hulling, irrespective of the type huller used. A not too wide a distribution would allow for better bran retention when hulling the grains thereby conveying the nutritional benefits to the people eating the millet rice rather than loosing it during processing. More about this can be found in related posts here.
Size and density grading in a community scale small millet processing unit provides a farmers with more nutritious and better quality food for their family, their livestock, their soil, and seeds for their next season.