To make bread using only flour and water, we focused on the day-one culture of sourdough. Wheat flour and water (133%) were incubated together at 29℃ for 24 h. The day-one culture contained total bacteria more than 10⁹ cfu/g, while yeast cell numbers were low at 10³ cfu/g and 10⁴ cfu/g. Sixteen strains were isolated from the day-one culture and identified by rapid microbial identification mass spectrometry systems (MALDI BDTM BioTyper^®, Bruker). Kosakonia cowanii was frequently isolated (14/16) from four types of the day-one culture. Bread could be made using K. cowanii SB and flour (bread flour and spelt flour) without adding sugars and yeast, and the specific volume was 2.54–2.64 cm³/g.