It was found that the peptide content of the main mash in the sake brewing process, seeded with kimoto, was higher than in that seeded with sokujo-moto, although the peptide content in kimoto was lower than in sokujo-moto. We investigated the underlying reasons. As a result, we found that the high concentration of free amino acids originating from kimoto decreased the peptide uptake ability of yeast cells in the main mash seeded with kimoto.