After threshing, grain still holds chaff and dust. Winnowing separates the heavy seed from the light debris using moving air. Toss the mixture into the wind and the chaff blows away while grain falls straight down.

The technique predates written history. Farmers used baskets, forks, or just their hands. Mechanical winnowers and combine harvesters now do the job with fans and screens, but the principle remains the same: density and airflow sort the mixture.

Traditional winnowing tools

• Woven baskets for tossing grain
• Wooden forks for lifting straw
• Winnowing trays with shallow rims
• Natural wind or hand fans

Done well, winnowing leaves clean grain ready for storage or milling. Done poorly, it leaves chaff that attracts insects and mould. Farmers judge the wind and adjust their toss accordingly, a skill learned through repetition.