Design Of Chinese Strong-Flavor Baijiu Solid State Fermentation Reactor For Real-Time Monitoring Of Process Parameters And Study On Fermentation Mechanism

Baijiu is one of the main liquor varieties in our country,and Chinese strong-flavor Baijiu occupies more than 50% of the Baijiu market.Traditional Chinese strong-flavor Baijiu is produced by solid state fermentation,which is closed in the mud pit for about60 days,and then through solid state distillation and other links.In the whole Baijiu production process,the mechanism of solid state fermentation stage is the most complex,and it is the most difficult to realize mechanization,intelligence and digital upgrade.The emergence of solid state fermentation reactors provided an important direction for solving current problems.Therefore,it is important to promote the development of the whole baijiu industry to design an above-ground reactor,which is close to the traditional production process and can meet both the scientific research and production needs.This paper aims to design a solid state fermentation reactor for Chinese strong-flavor Baijiu with real-time monitoring of fermentation parameters and explore the solid-state fermentation mechanism of Chinese strong-flavor Baijiu.The main research contents and conclusions are as follows:(1)A solid state fermentation reactor for Chinese strong-flavor Baijiu was designed.The main body of the reactor was made of food grade stainless steel.The reactor could use natural temperature rise to reach normal fermentation temperature,and real-time sampling and testing of fermented grains could be carried out through an independently designed transverse sleeve sampler.Yellow water drainage pipe was set at the bottom of the reactor,oxygen reduction potential detection pipe and temperature detection system were set on the wall,and oxygen cycle detection system was set on the top cover.The environmental parameters of fermented grains in the reactor could be monitored in real time.The experimental results showed that the system could detect the indexes of fermented grains in real time,and the flavor of base baijiu produced in the reactor was consistent with that of the traditional mud pit.(2)The traditional pit of Chinese strong-flavor Baijiu was tracked,and the samples of fermented grains at different fermentation time points(0,5,10,15,25,35,45 and60 days)were sampled by vertical samplers.The physicochemical,microbial communities and temporal and spatial evolution of the samples of fermented grains were detected and summarized.The correlations between physical and chemical indexes and dominant microbe genera,key volatile substances and dominant microbe genera,and microorganisms in fermented grains were analyzed.The results showed that: ○1 The moisture content,acidity and alcohol content were on the rise,p H was on the rise and then on the rise,and starch and reducing sugar were on the decline.There were numerical differences in the fermented grains of upper and lower levels,but the trends were similar.○2 A total of 40 esters,13 acids,24 alcohols,15 aldehydes and ketones,3 phenols,and 17 other volatile substances were detected in the upper layer of the fermented grains.A total of 38 esters,13 acids,23 alcohols,14 aldehydes and ketones,3 phenols,and 19 other volatile substances were detected in the lower layer of the fermented grains.Esters accumulated gradually in the later stages of fermentation and became the main components of volatile substances in fermented grains.○3 The Lactobacillus of genus and the Dipodascus of genus gradually dominated the microbial populations in fermented grains,and the abundance and diversity of microorganisms in fermented grains decreased with the fermentation time.○4 Moisture content,alcohol content,p H,reducing sugar,and starch content greatly affect the activity of microorganisms.Acetobacter,Bacillus,Lactobacillus and Dipodascus,Penicillium,Candida and Aspergillus of bacteria and fungi are closely related to volatile substances,which play an important role in the synthesis and accumulation of flavor substances in the whole stage of solid state fermentation stage.Most of the microorganisms in fermented grains were positively correlated,which was speculated to be the result of the long-term domestication of the microorganisms in the pit.(3)The fermentation process of fermented grains in the solid state fermentation reactor was tracked,and the indexes of fermented grains in the solid state fermentation reactor were studied.The results showed that: ○1 The moisture content and alcohol content of fermented grains in the reactor were significantly different from those in the traditional pit,and the content of starch,reducing sugar,acidity and p H were also slightly different from those in the traditional pit,but the trend and range of change were consistent on the whole.○2 The types of volatile substances detected in the reactor were relatively small.Among them,a total of 32 esters,15 acids,14 alcohols,14 aldehydes and ketones,4 phenols,and 13 other compounds were detected in the upper layer of the fermented grains.A total of 36 esters,16 acids,18 alcohols,10 aldehydes and ketones,6 phenols,and 11 other compounds were detected in the lower layer of the fermented grains,which were also in the later stage of fermentation.In the later stage of fermentation,the contents of esters gradually accumulated and became the largest volatile substances in the fermented grains.○3 Also at the later stage of fermentation,Lactobacillus of bacteria and Dipodascus of fungi took up the largest proportion.The abundance and diversity of microbial population decreased gradually with fermentation as in the traditional pit.○4 The temperature of fermented grains and oxygen reduction potential in the reactor also had important effects on microbial species.In the reactor,Lactobacillus,Acinetobacter,Bacillus,Dipodascus and Rhizopus had a close relationship to the fermentation flavor of fermented grains.Similar to traditional pit,the microbes in the reactor were mostly in positive interaction,which indicated that solid-state fermentation of Chinese strong-flavor Baijiu was a complex process of cooperative fermentation of multispecies.It is noteworthy that the microbial interaction in the reactor is obviously less complex than that in the traditional pit,which may be related to the quality of the pit mud and the service life of the reactor.