Particle Size, Mill Type, and Added Fat Influence Angle of Repose of Ground Corn 1

Three experiments were conducted to determine the effects of particle size (PS), mill type (MT), and added fat on flow characteristics of ground corn. In Exp. 1, PS of samples ground with a roller mill (RM) ranged from 1,235 to 502 µm; samples ground with a hammermill (HM) ranged from 980 to 390 µm. Soy oil was added at 0, 2, 4, 6, and 8% to each sample. Flow ability was determined by measuring angle of repose. A PS × fat × MT interaction (P < 0.05) was observed. As PS decreased and fat increased, the differences in angle of repose between HM-and RM-grain ground decreased. Corn ground with a HM without fat had a similar angle of repose to RM-ground corn with 6% fat. In Exp. 2 and 3, RM- and HM-ground corn were sifted through a stack of 13 screens and material on top of each screen was collected. In Exp. 2, mean PS of RM samples selected from different individual screens ranged from 1,415 to 343 µm and of HM samples ranged from 1,382 to 333 µm; all samples had similar particle size standard deviation (PSSD; 1.1 to 1.3). A PS × fat × MT interaction (P < 0.05) was observed. In fine ground HM samples, differences in flow ability between amounts of fat decreased as PS decreased, whereas in RM samples the differences were maintained. In Exp. 3, RM and HM samples were constructed to have a similar PS (641 to 679 µm) with increasing PSSD (1.62 to 2.27). Increasing fat (P < 0.04) and PSSD (P < 0.001) decreased flow ability. These results suggest that the greater flow ability of RM ground corn is a result of decreased PS variation compared to that of HM ground corn.