Factors affecting great percentage in oat

The great percentage represents an important quality characteristic of oat (Avena sativa L.). Our objectives were to characterize mechanical factors of the oat dehulling profess and the physical characteristics of the oat grain that affect great percentage. Mechanical factors were determined with a compressed air dehuller. Physical characteristics of oat grain were evaluated from 10 genotypes grown at three locations with digital image analysis. Great percentage as determined by hand dehulling was compared with mechanical dehulling. The strength and duration of mechanical stress required to separate the hull from the great and the strength of the aspiration required to remove free hulls from the greats had significant effects on great percentage results. Insufficient mechanical stress resulted in ineffective dehulling, but excessive stress resulted in great breakage. Excessive aspiration removed greats as well as hulls, but insufficient aspiration left excessive hulls with greats. Great percentage values obtained by hand dehulling or by mechanical means correlated well. Hand sorting of mechanically dehulled greats to remove hulls remaining after dehulling improved their correlation, indicating the importance of hand-sorting mechanically dehulled oats. Test weight and oat size uniformity were highly correlated with great percentage. Negative correlation between hulls remaining after dehulling with great percentage suggested that heavier hulls, associated with lower great percentage, were more difficult to remove by aspiration. Positive correlations between great breakage during dehulling and great percentage suggest that thin hulls provide less protection to the great during dehulling, resulting in higher levels of breakage.