Experiments were undertaken to study the mechanism of solid particle degradation by Bacillus coagulans NK1 in solid-state fermentation (SSF). The particle size reduction during the course of the fermentation and its corresponding effect (which indicates the substrate availability) on the production of enzymes was analyzed. The physical changes, such as water-holding capacity and moisture level, were analyzed at different time intervals during the course of the fermentation. The organism preferentially utilized the smaller particles having higher starch content throughout the course of the fermentation. The degradation was followed on larger particles toward the end of the fermentation. Maximum reduction in size as well as total weight of the substrate particle and optimal release of the major hydrolytic enzymes, such as alpha-amylase and xylanase, were observed around 36-48 hours of fermentation. A mathematical model has been proposed for the substrate particle size degradation during fermentation based on the heterogeneous noncatalytic reactions of chemical engineering.