Analysis of the Microbial Population of Makgeolli (Traditional Korean Rice Wine) during the Wine’s Fermentation Period

Introduction: Makgeolli has a unique taste and flavor due to fermentation, with many types of microorganisms being involved in the fermentation of the wine. Filamentous fungi hydrolyze the starch to glucose and yeasts convert the glucose to alcohol. Carbohydrate-metabolizing lactic acid bacteria (LAB) are also present in the beverage. It is important to understand the fermentation-specific microbial consortia present in Makgeolli for improving the wine’s quality and extending its shelf life. 

Purpose: Changes in the microbial communities of bacteria and fungi were monitored during the entire fermentation period of Makgeolli (12 days). 

Methods: We brewed Makgeolli in our laboratory. Samples were collected every 2 days during the fermentation period, and chemical indexes such as pH, alcohol content, and reducing-sugar levels were measured. The microbial community was analyzed using barcoded pyrosequencing with bacteria- and fungi-specific primers targeting the genes encoding 16S rRNA (bacteria) and 28S rRNA (fungi). In all, 46,986 sequence reads for bacteria and 17,945 sequence reads for fungi were used for the microbial analysis.

Results: During the fermentation process, LAB belonging to the genera Pediococcus, Weissella, and Lactobacillus dominated the microbial population from day 4 until the end of fermentation, and Saccharomyces dominated significantly during the entire fermentation period. The pH was 5.12 at the beginning of fermentation and gradually decreased until the end stage. Alcohol content increased rapidly from day 2 and remained constant from day 6, while the reducing-sugar content increased on day 1, but decreased dramatically on day 2.

Significance: The changes in chemical indexes correlate with the changes in the microbial population during Makgeolli fermentation. These results suggest that the microbial population influences the quality of Makgeolli.