Modeling of industrial-scale anaerobic solid-state fermentation for Chinese liquor production
Jin, Guangyuan ; Uhl, Philipp ; Zhu, Yang ; Wijffels, René H. ; Xu, Yan ; Rinzema, Arjen - \ 2020
Chemical Engineering Journal 394 (2020). - ISSN 1385-8947
Chinese liquor - Heat transfer - Mathematical modeling - Product inhibition - Solid-state fermentation - Temperature modeling
Traditional solid-state fermentation processes can give fluctuating product quality and quantity due to difficulties in control and scale up. This paper describes an engineering study of an industrial-scale anaerobic solid-state fermentation process for Chinese liquor (Baijiu) production, aimed at better understanding of the traditional process, as an initial step for future optimization. This mixed-culture fermentation is done in 0.44-m3 vessels embedded in the soil. At this scale, the fermentation is limited by product inhibition. We developed mathematical models based on the Han-Levenspiel equation for product inhibition, with parameters derived from measured data. The models accurately predicted the concentrations of starch and dry matter. A model with radial conduction into a small soil volume around the fermenter and consecutive vertical conduction into the underlying soil accurately predicted the pit temperature in the heating and cooling phases. This model is very sensitive to the values used for the enthalpies of combustion, meaning that direct measurement of the heat production rate would be preferable. In the industry practice, the fermenter volume can be from around 0.20 to 15.00 m3. The model predicts that overheating will occur not only in larger fermenters, but also in the 0.44-m3 fermenters when the soil temperature is high in summer. Our model predictions are consistent with observed behavior in the industry. Our findings can be used to improve this traditional process, as well as similar systems.
Water dynamics during solid-state fermentation by Aspergillus oryzae YH6
Jin, Guangyuan ; Zhu, Yang ; Rinzema, Arjen ; Wijffels, René H. ; Ge, Xiangyang ; Xu, Yan - \ 2019
Bioresource Technology 277 (2019). - ISSN 0960-8524 - p. 68 - 76.
Aspergillus oryzae - Nuclear magnetic resonance (NMR) - Solid-state fermentation - Water activity - Water dynamics
Water is crucial for microbial growth, heat transfer and substrate hydrolysis, and dynamically changes with time in solid-state fermentation. However, water dynamics in the solid substrate is difficult to define and measure. Here, nuclear magnetic resonance was used to monitor water dynamics during the pure culture of Aspergillus oryzae YH6 on wheat in a model system to mimic solid starter (Qu or Koji) preparation. During fermentation, overall water content gradually decreased from 0.84 to 0.36 g/g, and water activity decreased from 0.99 to 0.93. Water content in different state (bound, immobilized and free) changed differently and all moved to more “bound” direction. The internal water distribution over the substrate matrix also showed a faster reduction inward both in the radical and axial direction. Our findings provide the prerequisites for optimal processes where water dynamics in solid-state fermentation can be monitored and controlled.