Effect of Drum and Concave Characteristics and Crop Moisture on Cumin Threshing Quality

Cumin is an annual plant suitable for dry and semi-dry regions. It is harvested at two stages to prevent seed shedding. First, the cumin bushes are harvested by hand or using a scythe. After drying, the cumin bushes are beaten with a stick or trampled using animals or a small tractor. This harvesting method is time consuming, requires intensive labor and is an incomplete threshing process resulting in crop loss and poor quality. Prior to developing a cumin thresher, the efficiency factors of cumin threshing were investigated. This research studied the effect of moisture content, drum type and speed, feed rate and space between the drum and concave on weight percentage of separated seeds, shattered stems and damaged seeds. The results showed that the percentage (by weight) of the separated seeds decreased from 92.85% to 90.39% when moisture content increased from 7% to 13%. The percentage of damaged seeds (by weight) decreased as moisture content increased. However, by increasing drum speed from 700 to 900 RPM, the amount of separated seeds, shattered stems and damaged seeds increased. There was no significant effect of drum type on the percentage of separated seeds (by weight), but there was a significant effect on shattered stems and damaged seeds. It can be concluded that the rub-bar drum was better than the rasp-bar drum. The rub-bar drum, 900-RPM drum speed and 7% moisture content were the most suitable conditions for threshing cumin.