Solid-state fermentation for Chinese liquor production

Solid-state fermentation has been used for thousands of years in Orient to produce foods and beverages. However, poor understanding of these fermentation processes, especially of the engineering aspects, hampers the modernization needed to improve process safety, product quality and production efficiency. Chinese liquor (Baijiu) production is a typical example of traditional solid-state fermentation. We use it as an example to study engineering principles of traditional solid-state fermentation including both Qu starter (a sort of Koji) preparation (aerobic) and alcohol formation (anaerobic). First, we addressed the important research directions including engineering aspects. Then we studied the water dynamics during Qu preparation process through a model fermentation system with in-situ and online measurement (NMR) of water content, migration, and distribution during the fermentation. The outcomes give insight into the association of water with microbial growth and heat transfer. To better understand the engineering mechanism including heat transfer during ethanol formation, wo built a simple mathematical model based on Han-Levenspiel equation for product inhibition. The simple models can accurately describe the fermentation process. However, still the most influential variables are not found by the mathematical model. Then statistical model based on a large data set obtained from year-round production. The result shows that the starting month is one of the most significant factors to the yield and the reason could be the lactic acid (bacteria). The scientific principles behind will benefit the liquor industry in particular, and the (food) biotechnology sector in general. Still big space exists for further in-depth understanding of engineering and process control of Chinese liquor solid-state fermentation in the future.