Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/10/2007
Publication Date: 5/1/2007
Citation: Doehlert, D.C., Wiessenborn, D.P. 2007. Influence of physical grain characteristics on optimal rotor speed during impact dehulling of oats. Cereal Chemistry. 84:294-300. Interpretive Summary: Oats must be dehulled before they can be processed for human consumption. Commercial operations use the impact dehuller for this purpose. During impact dehulling, oats are fed into a spinning rotor, which expels the oats against an impact ring. The force of the impact frees the oat from its hull. Commercial oat mills fractionate oats according to their size and change the rotor speed according to the size of the oats being dehulled. Here, we report relationships between oat kernel size and the optimal rotor speed needed to obtain the best dehulling yields. Although we expected the most massive kernels to require the slowest rotor speeds for optimal dehulling, instead we found that it was the most dense oat kernel fractions that required the slowest speeds for optimal dehulling. Oat density, generally referred to as test weight, is an important quality characteristic, and is routinely measured in oats bound for markets. The relationship between test weight and dehulling efficiency emphasizes the importance of test weight in oat production.
Technical Abstract: Central to commercial oat (Avena sativa L.) processing is impact dehulling. During impact dehulling, oats are fed into a spinning rotor that expels the kernels against an impact ring. The force of the impact frees the groat from the hulls. In this study we have examined the effects of kernel characteristics and rotor speed on oat dehulling using an impact dehuller. We separated kernels of three cultivars (Gem, CDC Dancer, Ronald) according to size by sieve separation (separation by width), disk separation (separation by length) and by gravity table (separation by density). Kernel size was analyzed by kernel mass, digital image analysis and test weight. Fifty-gram samples were adjusted to 9 percent moisture and dehulled at four different rotor speeds. Groat percentage, dehulling efficiency and groat breakage were measured after dehulling. In general, oats with higher test weights dehulled more efficiently at slower speeds, regardless to kernel mass. Groat breakage increased with rotor speed and with kernel mass. Analysis of groat yield indicated that adjusting dehulling conditions according to kernel size improved yields over optimal dehulling conditions for unfractionated kernels for at least some genotypes. Data suggested that kernel mass is not necessarily the best criterion for size separation, and that kernel density may be more important in determining the optimal rotor speed for impact dehulling.