wahat are the principles of  handpicking,threshing,sieving and winowing

Hi,

Hand-picking and sieving are based on the different size of the two components mixed which can be picked by using hands only or by filtering through the sieve.

Winnowing is based on the difference in mass of the grain and its husk. Husk being lighter flows in direction of air and the grain being heavier falls straight.

Winnowing is based on the fact that when grains are beaten on the ground with force, the chaff of the grain loosen and thus can be separated.