We developed a novel medium to discriminate wild yeast from sake yeast easily. The discrimination was based on the difference of acid phosphatase activity between wild yeast and sake yeast under a condition of a high concentration of inorganic phosphatase in the medium. We were able to visualize a difference in the acid phosphatase activity of colonies on a plate with 5-bromo-4-chloro-3-indoly1 Phosphate Disodium Salt added to the medium. The optimal concentration of KH₂PO₄ in the medium was 6.0 mmol/L or more.