M17 medium is a widely used culture medium for lactic streptococci. When it was first reported by Terzaghi & Sandine (1975), one of the reference media used for comparison was T5 medium (Thomas et al., 1974). T5 medium contains phosphate salts and shows buffering capacity equivalent to that of M17 medium, making it an excellent choice for lactic streptococci that produce large amounts of lactic acid. However, T5 medium was found to form a precipitate, and the authors concluded that the clear M17 medium was superior. Fifty years later, M17 medium has become the standard. When I read the description that T5 medium produces a precipitate, I thought, “Hmm, is …