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Baijiu is a unique and traditional distilled liquor in China. Flavor plays a crucial rule in baijiu. Up to now, the research on the flavor of baijiu has progressed from the identification of volatile compounds to the research on key aroma compounds, but the release mechanism of these characteristic compounds is still unclear. Meanwhile, volatile compounds account for only a tiny fraction, whereas ethanol and water account for more than 98% of the content in baijiu. By summarizing the ethanol–water hydrogen bond structure in different alcoholic beverages, it was found that flavor compounds can affect the association strength of the ethanol–water hydrogen bond, and ethanol–water can also affect the interface distribution of flavor compounds. Therefore, the research on ethanol–water microstructure in baijiu is helpful to realize the simple visualization of adulteration detection, aging determination and flavor release mechanism analysis of baijiu, and further uncover the mystery of baijiu. [ABSTRACT FROM AUTHOR]

• The feruloyl esterase activity in different layers of Jiupei at different fermentation times were determined and tracked. • The microorganisms with feruloyl esterase activity were screened and identified in Jiupei of sesame-flavor baijiu. • The conditions of enzyme production were optimized by liquid fermentation. Baijiu is a national beverage in China. Some functional compounds have been identified in baijiu, one of which is ferulic acid. One route for in situ ferulic acid synthesis is catalysed by feruloyl esterase from microorganisms using baijiu raw materials as substrates. However, few studies have focused on microorganisms obtained from baijiu that have feruloyl esterase activity. In this work, microorganisms with feruloyl esterase activity were screened in the fermented raw materials of baijiu. Four different microorganisms with feruloyl esterase activity were identified, and one strain, designated J1, showed high feruloyl esterase activity. The strain J1 belonged to the genus Acetobacter and showed the closest relationship with Acetobacter fabarum and Acetobacter lovaniensis. The feruloyl esterase production capacity of J1 was confirmed, and the fermentation conditions were optimised. The optimal enzyme production conditions for the highest feruloyl esterase activity required an initial fermentation pH of 7.0 at 30 °C, an inoculation volume of 10 %, and culturing for 24 h. [ABSTRACT FROM AUTHOR]