Evaluating Pellets Produced on Three Distinct Pellet Mill Series

It is well accepted that pellet quality can change based on varying pelleting parameters. However, there is limited research evaluating differences among different types of pellet mills. The purpose of the experiment is to compare percentage fines and Pellet Durability Index (PDI) of pellets produced on three different pellet mill models (medium scale: 3016-4, small scale: 1012-2, and benchtop: CL-5; California Pellet Mill Co., Crawfordsville, IN). A single swine finishing diet particle size (500 µm ± 50µm) was pelleted through 3 different runs on each of the pellet mills, with hot pellet temperature (88°C ± 2°C), conditioner retention time (30 s), die size (4 mm × 22 mm), length/diameter ratio (5.6), and throughput (60% of rated throughput) held constant. One composite pelleted feed sample was collected per run, cooled, and analyzed for PDI according to the Holmen NHP100 (TekPro Ltd., Norfolk, United Kingdom) and the Modified PDI method (ASABE S269.4, 2007 modified with three 19 mm hex nuts). Percentage fines were also determined as the percentage of a 4.5-kg sample that flowed through a #6 U.S. screen. Data were analyzed using the GLIMMIX and CORR procedures of SAS v. 9.4 (Cary, NC). Pellet mill type impacted (P < 0.001) PDI as measured by the Holmen NHP100 (37.7, 57.6, and 93.8 for 3016-4, 1012-2, and CL-5, respectively). Similarly, pellet mill type also impacted (P < 0.001) PDI as measured by the Modified PDI method (59.2, 67.3, and 91.2 for 3016-4, 1012-2, and CL-5, respectively). Percentage fines was strongly correlated with PDI as measured by both the Holmen NHP100 method (P = 0.009; -0.807) and Modified PDI method (P = 0.018; -0.759). These data underscore that clear differences exist in pellet quality among different pellet mills, even those from the same manufacturer when pelleting parameters are held constant. Caution should be used when comparing pellet quality among pellet mill type.