Monitoring of rheological parameters in the anaerobic fermentation process to obtain bioethanol from craft brewer’s spent grain using brewer’s spent yeast and Saccharomyces cerevisiae S-04

In this study, the physical changes during the integral process for obtaining bioethanol were analyzed. The feasibility of using brewer’s spent yeast (BSY) was evaluated. BSY was utilized as an inoculum with craft brewers’ spent grains (CBSG) to reduce the economic and environmental impact of the waste generated in the craft beer industry and produced bioethanol. In Mexico, it is a productive sector largely neglected by academic institutions and does not receive support in the management and disposal of its byproduct. Enzymatic-ultrasonic pretreatment was implemented to increase the availability of reducing sugars (RS) through variations in the amount of cellulase enzyme (0.3, 0.5% w/v), hydrolysis time (6, 8 h), and ultrasonic amplitude (15, 20%). Finally, alcoholic fermentation was carried out with BSY at three inoculum concentrations, 0.5, 0.8, and 1.0% v/v, and the results were compared with those of a control with the commercial yeast Saccharomyces cerevisiae S-04. In all stages, the rheological properties of the substrate, such as density, viscosity, consistency index, and performance index were monitored. It is recommended to use 0.5% cellulase for 8 h, since under these conditions, a bioethanol production of 7.71% with 1.0% BSY was obtained (8.67 g bioethanol/100 g raw material). In addition, the kinetic parameters of yeast cell growth were obtained through the Gompertz model to determine the growth rate and lag time. In turn, the rheological parameters allowed the establishment of control conditions and operating regions that determined the end of the process and the generation of bioethanol.