The great percentage represents an important quality characteristic of oat
(Avena sativa L.). Our objectives were to characterize mechanical factors o
f the oat dehulling profess and the physical characteristics of the oat gra
in that affect great percentage. Mechanical factors were determined with a
compressed air dehuller. Physical characteristics of oat grain were evaluat
ed from 10 genotypes grown at three locations with digital image analysis.
Great percentage as determined by hand dehulling was compared with mechanic
al dehulling. The strength and duration of mechanical stress required to se
parate the hull from the great and the strength of the aspiration required
to remove free hulls from the greats had significant effects on great perce
ntage results. Insufficient mechanical stress resulted in ineffective dehul
ling, but excessive stress resulted in great breakage. Excessive aspiration
removed greats as well as hulls, but insufficient aspiration left excessiv
e 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. Tes
t weight and oat size uniformity were highly correlated with great percenta
ge. Negative correlation between hulls remaining after dehulling with great
percentage suggested that heavier hulls, associated with lower great perce
ntage, were more difficult to remove by aspiration. Positive correlations b
etween great breakage during dehulling and great percentage suggest that th
in hulls provide less protection to the great during dehulling, resulting i
n higher levels of breakage.