Effects of corn kernel hardness and grain drying conditions on particle size when grinding using a roller mill or hammermill

Corn kernel hardness and grain drying conditions may affect particle size and distribution subsequent to grinding, which could affect feed mill productivity and animal performance. In the present study, the effects of two corn hybrids (Dekalb 68-05 and Dekalb 65-20) with differing kernel hardness (average and hard respectively) and three grain drying conditions (35, 80, and 120°C) on the geometric mean (Dgw) and standard deviation (Sgw) of particle size were assessed by the sieving method. For roller milling, four combinations of roll gap settings were studied (0-0, 25-20, 30-30, and 35-35.) For hammer-milling, three hammermill speeds were evaluated (900, 2,400 and 3,600 rpm) in each case grinding through a 12-12 screen combination. Treatments were arranged in a 2 x 3 factorial design with two corn hybrids and three grain drying temperatures. There were three replicates per treatment combination. Data were analyzed in a completely randomized design and mean separation was done using Tukey’s test. Results obtained by roller milling with 0-0 and 35-35 roll gaps showed that harder corn kernels yielded higher (P < 0.001) Dgw values in comparison to corn with average kernel hardness when dried at 35°C. Similar response was observed when the corn was dried at 120 °C.

In addition, the Sgw was reduced (P < 0.001) when using corn with harder kernels that was dried at 80 and 120°C and milled at 0-0 (2.39 vs. 2.53), 30-30 (2.41 vs. 2.65), and 35-35 (2.34 vs. 2.69), respectively. In contrast, no effects (P > 0.05) were observed on Sgw when corn dried at 120°C was ground by the hammer mill. Higher (P < 0.001) Sgw was detected in the corn with average hardness that was dried at 35 and 80°C and milled at 2,400 and 3,600 rpm (3.84 vs. 3.45; and 3.21 vs. 3.03 respectively). The Dgw was higher (P < 0.001) in corn with harder kernels dried at 120°C when ground at 2,400 (744 vs. 594 µm) and 3,600 rpm (556 vs. 424 µm) respectively. Generally, corn with harder kernels and dried at 120 °C had higher Dgw and corn with average hardness had greater Sgw independently of the grinding method. In conclusion, kernel hardness of corn and grain drying temperatures affected the particle size and distribution subsequent to grinding in both a roller mill and hammermill.

Key Words: roller mill, hammermill, grinding method, Sgw, Dgw.

Abstract presented at the International Poultry Scientific Forum 2019 in Atlanta, USA.