Yeast Nitrogen Base (YNB) media have been prepared according the formulae of Wickerham (1943-51) and Burkholder (1943). YNB is a well defined composition of salts, vitamins, amino acids and a nitrogen source for a vigorous growth of Sacharomyces cerevisiae. Yeast Nitrogen Base without amino acids (YNB w/o AA), Y2025, is used for selecting yeasts based on amino acid and carbohydrate requirements. In Y2025, Ammonium Sulfate is included as a readily available nitrogen source for nitrogen assimilation. The medium includes all other vitamins, mineral salts and trace elements required for a vigorous growth of yeast cells. Compared to full YNB medium, Y2025 lacks Histidine, Methionine and Trypthophan. In combination with "Drop Out" medium supplement mixtures, Y2025 provides an excellent medium to cultivate and select auxothophic strains of yeast that requires the addition of essential nutrients like amino acids and/or vitamins. , Application: , For carbon assimilation tests in the characterization and identification of yeasts., , Note: The addition of a carbon source like glucose, galactose or raffinose is required.