This study was conducted to improve the performance of a foreign materials separating system in a middle-sized pepper harvester. The floating speed of pepper fruit and foreign materials was measured. Wind speed at each position of the winnowing machine was measured with the addition of wind guides. The efficiency of foreign materials separation and the ratio of stagnant foreign materials were analyzed by the addition of wind guides and the position of a collection guide. The results of the factor experiments were analyzed by two-way analysis of variance (ANOVA). The experimental results are as follows:

1) The floating velocity of pepper fruits and the foreign material in the raw and dried samples were measured for three pepper varieties. The results showed that the floating velocity of the raw pepper fruit was 11.5-14.3 m/s, the raw pepper stems was 10.9-12.5 m/s, the raw pepper leaves was 3.45-5.42 m/s, the dry pepper fruit was 10.89-12.1 m/s, the dry pepper stems was 8.35-9.54 m/s, and the dry pepper leaves was 2.74-5.14 m/s.

2) To evenly distribute the wind direction, three or five wind guides were added. The wind speed at 18 points was measured depending on the location of the existing wind winnowing machine and a winnowing machine with wind guides. After the wind guides were added, the deviation of the left and right wind speeds was reduced.

3) Good separation of foreign materials in the separating system was a function of the high separation efficiency of the foreign materials and a low ratio of stagnant foreign materials. A statistical analysis of the separating performance of the factor test results was conducted. As for the addition of wind guides, the separation efficiency of foreign materials was an average of 25.40?47.00% of the existing winnowing machine, which was higher than the wind winnowing machine with added wind guides. As for the collection guide position, the separation efficiency of the foreign materials was high at an average of 31.07?47.00% in the Front-Middle condition and the ratio of stagnant foreign materials was low, at an average of 0.00?3.00% in the Back-High condition. The existing winnowing machine had a high separation efficiency for foreign materials. However, considering the stagnant foreign material, the winnowing machine with three wind guides was judged to be advantageous. The collection guide position in the Front-Middle condition was also advantageous.

4) In this experiment, manufactured samples were used, but it is necessary to perform additional performance tests to verify the separation performance in field tests. In addition, since foreign materials were collected due to insufficient airflow rate, it is necessary to increase the size of the impeller and increase the airflow rate in further experiments.