Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/1999
Publication Date: N/A
Interpretive Summary: The oat kernel is normally covered with hull after harvest, which is not edible. The edible portion of the oat kernel is called the groat. The groat percentage is the proportion of the oat kernel that is groat, and represents the economic yield from that sample of grain. Groat percentage can be determined by hand dehulling of a sample of grain, or by the use of one of several mechanical dehullers. We have found that the method used to dehull oats and the conditions of mechanical dehulling can strongly affect the groat percentage value obtained. Conditions that reduce the mechanical stress to the grain result in less efficient dehulling, but excessive mechanical stress results in breakage of the groats. Too little aspiration, required to remove the free hulls from the groats results in hulls remaining with the groats, whereas too much aspiration removes small groats as well as hulls. Optimal conditions selected represent a compromise between adverse extremes. After selecting what we considered to be optimal conditions, we measured groat percentage in 10 oat cultivars, grown at 3 locations in 1997. We also measured some quality characteristics of the oat grain, including detailed measurements of the grain architecture, by digital image analysis, to determine characteristics associated with higher groat percentage. We found that test weight and kernel size uniformity were correlated with groat percentage. We also noted that cultivars that had lower groat percentages, tended to suffer less broken groats, suggesting thicker hulls may protect the groat during dehulling.
Technical Abstract: The groat percentage of oat grain represents the economic yield from the oat. We have sought to characterize physical characteristics of the oat affecting groat percentage, as well as mechanical factors of the dehulling process that affect experimentally obtained values. Mechanical factors demonstrated to affect values of groat percentage include the strength and duration of mechanical stress required to separate the hull from groat, and the strength of the aspiration required to remove free hulls from the groats. Insufficient mechanical stress resulted in ineffective dehulling and excessive hull remaining with groats after dehulling. Excessive stress resulted in groat breakage and their subsequent removal by aspiration. Excessive aspiration removed groats as well as hulls, but insufficient aspiration resulted in excessive hulls remaining with groats. Groat percentage values obtained by hand-dehulling or by mechanical means correlated well, but the hand sorting of mechanically-dehulled groats to remove hulls remaining after dehulling improved their correlation. Test weight and oat size uniformity were highly correlated with groat percentage. Negative correlations between hulls remaining after dehulling with groat percentage suggested that heavier hulls, associated with lower groat percentage, were more difficult to remove by aspiration. Positive correlation between groat breakage during dehulling and groat percentage suggest that thin hulls provide less protection to the groat during dehulling, resulting in higher levels of breakage. Results suggest that hand sorting of mechanically dehulled groats to remove hulls remaining is required to obtain the most reliable groat percentage values.