AIMS: This study aimed to clarify the cause of quality reduction in Korean sourdough after successive back-slopping. METHODS AND RESULTS: ) and produced large amounts of lactic acid, whereas L. brevis and L. curvatus consumed maltose slowly and L. curvatus was poorly tolerant to lactic acid. CONCLUSION: The results indicate that competition exists between the lactic acid bacteria in sourdough during the back-slopping process, and microbial succession by acid-tolerant species results in quality reduction of sourdough. SIGNIFICANCE AND IMPACT OF THE STUDY: This study uncovered the cause of microbial changes during the propagation of Korean sourdough and proposed a strategy to develop starters to produce high-quality bakery products.