Screening And The Role Of Exogenous Microorganisms In Beer

Nearly all wild yeasts were able to undesirable influence on the beer flavor. Some wild yeasts did not influence the quality of the beer, but their presence indicates that the beer was still contaminated in some aspects. All equipment and materials could not be completely sterilized during the fermentation process, thus susceptible to contamination of wild yeast. Saccharomyces cerevisiae could be contaminated by wild yeast when they used repeatedly.The traditional identification methods of yeast were mainly morphological, physiological and biochemical identification and it usually took a long time. It was not easy to distinguish some wild yeast which had the similar traits with saccharomyces cerevisiae. PCR technology was currently used in the classification and identification of yeast, but its operation was complex and had some limitations. Design adding wild yeast in the beer fermentation process. Found that the influence of the fermentation process by detected the beer flavor and so on. So we can determine whether the fermentation process was contaminated by wild yeast.The content of flavor substances in beer can be measured by headspace gas chromatography. The main volatile flavor substances in beer can be carried out in qualitative and quantitative analysis with high purity nitrogen as the carrier gas. Through experiments, the best experiment parameters were established:sample balance temperature was 60℃; sample balance time was 30 min; the amount of NaCl was 3 g; inlet temperature was 160℃; detector temperature was 180℃; the oven temperature program was 3min at 45℃ and then 10℃/min to 180℃ for 3 min; the column flow was 1.6 mL/min. In the optimized detection condition, the calibration curves were protracted and the correlation coefficient ranged from 0.9938 to 0.9994.Five wild yeasts found of the sake of beer were isolated and purified. The 15# wild yeast belongs to Pichia myanmaensis (AB 126678.1) by sequence analysis and identification of 26S rDNA domain gene. The 15# wild yeast was chosen to experiment of a higher simie temperature, poor degree of aggregation and the more obvious changes. Different wild yeast would make the different influence of flavor through the analysis of the concentration of eight flavor substances in beer. Wild yeast could change in the regularity of flavor by adding different proportions of wild yeast. The concentration of ethyl caproate and ethyl caprylate was still 30 percent higher than the blank control when the 15# wild yeast was added 0.1 percent.