Winnowing is the process of separating grain from chaff. For this purpose, the customary practice is to make use of natural air currents, thus leaving the farmer at the mercy of nature's vagaries. Foodgrains such as ragi, jowar, etc, are harvested in the months of September, October, March and April. Weather conditions during these months are such that processing of foodgrains is rendered quite a difficult task, involving a loss in the quality and quantity of products, both grain and husk.

A study of the existing designs and equipment was made. This showed the availability of various units which are mostly inadequate and inappropriate for the winnowing needs of the average farmer, e.g., (a) combines/grain cleaners which are power operated and prohibitively expensive; (b) small imported winnowers, meant only for paddy, which involve high operating costs.

This study as also a preliminary survey conducted in some of the areas in Karnataka State showed that :

1. available units are capital intensive and sophisticated, the result being that their market is limited.

2. they are useful only for certain types of grain like paddy, jowar, while they cannot be used for other grains like ragi, coriander etc.

This information was used to lay down broad specifications regarding cost-effectiveness, versatility and simplicity in the design of the winnower.

A somewhat sophisticated test unit was designed and fabricated so as to collect information on various parameters such as rate of air supply, rate of feed of stock, etc. The unit is amenable to both manual and power operation. It was tested with samples in the laboratory and a number of experiments varying different parameters were conducted. A continued extensive field test in a few villages was also carried out.