Determination of Optimal Pelleting Parameters to Maximize Pellet Durability of Reduced-Fat DDGS

Reduced-fat distiller’s dried grain with solubles (DDGS) is commonly pelleted and fed as a dairy supplement, but pelleting 100% DDGS is not common. The objective of this 3 phase experiment was to determine pellet mill manufacturing parameters to optimize pellet quality of a commercially-available reduced-fat (6.11% crude fat) DDGS source (Dakota Gold™, POET Nutrition, Sioux Falls, SD) pelleted on a 3000 series pellet mill (3016-4 California Pellet Mill Co., Crawfordsville, IN). The three phases were 1.) 3 × 2 factorial with three conditioning temperatures (49°C, 66°C, 82°C), and two retention times (30s vs. 60s), 2.) Two die-diameter sizes with varying Length/Diameter (L/D) ratios (5.5 and 10.0). A larger L/D ratio indicates a higher degree of friction upon the feed flowing through the die-hole. 3.) 3 × 2 factorial with three production rates (1,360 kg/hr., 2,270 kg/hr., 3,175 kg/hr.), and two die RPM (166 vs. 254). Pellet samples were collected, cooled, and analyzed for Pellet Durability Index (PDI) according to the Holmen NHP100 (TekPro Ltd., Norfolk, United Kingdom). For PDI analysis, 100 g of pellets, sifted on a U.S. sieve screen, are placed in the machine’s perforated mesh hopper; pellets are blown by air to create friction for 60 s, while the fines filter through a chamber. The percentage pellets remaining is used to calculate PDI. Data were analyzed using the GLIMMIX procedure of SAS v. 9.4 (Cary, NC). Phase 1 results indicate, the interaction (P = 0.235), retention time (P = 0.601), or temperature (P = 0.052) did not impact PDI. The remaining phases were processed at 66°C with a 30s retention time. Phase 2 having a varying L/D Ratio impacted (P = 0.011) PDI (87.10 vs. 93.27 for L/D ratio 5.5 and 10.0, respectively). A die with an L/D ratio of 10.0 was used in Phase 3 due to a 6.17 percentage point improvement compared to a. 5.5 L/D ratio die. Phase 3 results indicate neither the interaction (P = 0.642) nor production rate (P = 0.558) impacted PDI, the faster die RPM improved (P = 0.0334) PDI (95.89 vs. 94.46 for die-RPM 1,800 and 1,200, respectively). These results suggest that of the parameters tested, reduced-fat DDGS have optimal pellet durability when pelleting on a die size of 10.0 L/D Ratio with a die rotating at 254 RPM. Temperature, retention time, and production rate evaluated in this study did not impact PDI when performing analysis by the Holmen NHP100.