Development of sour beer brewed by lactic acid bacteria isolated in Shizuoka Prefecture

Sour beer production has been gradually increasing in Japan. Generally, sour beer is brewed by natural fermentation, long-term aging in wooden barrels, or by the kettle souring method. Here, the kettle souring method was selected because this method has advantages over other methods in terms of handling and preventing contamination at the brewing site. To develop a sour beer unique to Shizuoka Prefecture, lactic acid bacteria isolated in Shizuoka and a beer yeast Saccharomyces cerevisiae NMZ-0688 that was developed previously, were utilized. Four optimal strains of lactic acid bacteria (Lactiplantibacillus plantarum TIG-0372, L. plantarum NMZ-1139, Lacticaseibacillus casei TIG-0429, and Schleiferilactobacillus harbinensis NMZ-1200) were selected from 147 isolated strains with high lactic acid productivity at 40 degrees C after preculturing at 30 degrees C. Yeast resistant to 2-deoxyglucose was reared from S. cerevisiae NMZ-0688 to improve the fermentation ability of the wort. The 2-deoxyglucose-resistant yeast increased the fermentation efficiency to a level equivalent to that of commercial beer yeast and was selected as the optimal strain. Eight types of small-scale brewing tests were performed with various combinations of these strains. Sensory evaluation by experts showed that the sour beers brewed by microorganisms from Shizuoka Prefecture had a fruity aroma, mainly due to isoamyl acetate, and a refreshing sour taste, which was attributed to the lactic acid.