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Effects of grain size, shape, and hardness on drying rate and the occurrence of stress cracks. Tae Hoon
Kim (1), J. G. Hampton (2), Linus Opara (3), A. K. Hardacre (4), and B. MacKay (5). (1) Seed Technology
Centre, Massey University; (2) NZ Seed Technology Institute, Lincoln University; (3) Institute of
Technology and Engineering, Massey University; (4) Crop & Food Research Institute; (5) Institute of
Natural Resources, Massey University.
The effects of grain hardness and morphological factors
(grain size/shape) on single grain drying rate and the development over time of stress cracking (SC) in maize grain
were investigated. The effects of hybrid and grain size/shape on SC were significant, and this suggested that
removing small and rounded grains could reduce checking by up to 40 to 50% in some dent maize hybrids.
The results also showed that SC developed over time during cooling after drying, and not during drying or
immediately after the finish of drying. The extent and rate of development of SC differed significantly
among the hybrids and grain size/shape categories. Very few stress-cracked grains were found immediately
after drying and some grains became single or double fissured during the first 30 to 60 minutes after drying.
Single and double SCs progressed into multiple or checked SC, and these were in the majority at the end by
72-hour after drying irrespective of hybrids and grain size/shape categories. The Morgan-Mercer-Flodin
(MMF) models indicated that there were significant differences in the rate of increases in checking and the
extent of checking among different maize hybrids and grain size/shape categories. Within grain size/shape
categories, checked SC developed to a greater extent and faster, in small and rounded grains than large and
flat grains. However, a significant reduction of SC after tempering and slow cooling following high
temperature drying was found, indicating that instead of drying temperature, how to deal with maize grain
after drying determines the severity of SC.
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