Impact of disk milling on fermentation performance and in-situ fiber conversion in dry grind ethanol process

In the corn dry grind ethanol process, dry corn is ground, mixed with process water to make slurry, which is processed for conversion to ethanol. Further grinding of corn in the slurry form can increase enzyme accessibility, leading to higher ethanol production. Fine grinding potentially also acts as pretreatment for fiber conversion in the dry grind process. The objective of our study was to evaluate the effect of disk milling of corn slurry to improve conversion of starch and fiber to ethanol in the dry grind process. Disk milling of slurry prepared from corn ground using 3 mm hammer mill sieve (similar size as used in commercial dry grind process) increased post-fermentation ethanol concentration by 4.9%. However, improvement in ethanol concentration was not observed by disk milling of slurry prepared from ground corn produced using 0.5 mm hammer mill sieve. Grinding corn to a small particle size prior to disk milling released most of the bound starch making disk milling of slurry ineffective in releasing additional starch. Cellulase addition in dry grind process resulted in an increase in ethanol concentration in fermentation and 30.8% decrease in neutral detergent fiber content in the unfermented material. Addition of 10 and 30 FPU/g fiber cellulase in fermentation increased ethanol yield by 4.3 and 6.7% respectively. Combining disk milling with cellulase addition during fermentation improve the dry grind process with only cellulase addition.