Microbial and physiochemical changes during the incubation of fen-Daqu

Fen liquor is typical of Chinese light-flavor liquor, which is fermented from sorghum with Fen-Daqu powder. Fen-Daqu is a saccharifying agent and fermentation starter obtained by natural solid-state fermentation under non-sterile conditions. The standard plate count and the online measurement methods were used to enumerate the surviving microorganisms, and measure the physiochemical in Fen-Daqu during the incubation. Total counts of mesophilic aerobic bacteria (30 °C and 55 °C), bacterial endospore (30 °C and 55 °C), lactic acid bacteria, enterobacteriaceae and fungi starting with minimum level around 106 , < 104 and 105 cfu/g and attaining maximum around 1011, 109 , 109 , 109 , 107 , 105 and 108 cfu/g, respectively. During the incubation of Daqu the microorganisms increased from Woqu to Liangmei periods and gradually decreased during the later phases. The pH in Daqu was increased over time during the incubation. The total acidity in Daqu increased and reaches to maximum at Shangmei phase (around 4.5 g lactic acid per kg Daqu) and then gradually decreased over the time. The relative humidity in incubation room was reduced from around 100 % to around 20 %. Temperature in incubation room was increased over time from the first to middle period and decreased in the Yangqu phase. Temperature in Daqu inner was rapidly increased from around 20 to 40 ºC at Shangmei phase, dropped to 30 ºC at Liangmei phase, and then increased gradually until reached to maximal 52 ºC at Dahuo phase, finally decreased to original temperature (25 ºC). The moisture was decreased from around 45 % to around 10 % during successive phases of incubation. Based on these results, a microbiological regulation for the production of Fen-Hongxin Daqu is proposed.