Yeast Nitrogen BaseYeast Nitrogen Base is based upon the formulation of Yeast Agar except that Ammonium Sulfate is the sole nitrogen source and that addition of carbon source is required. The medium may be used to test carbon assimilation in the presence of a carbon source like glucose, galactose or raffinose. Suspend 6. 9 gram powdered medium in 1 litre distilled water Store dry at room temperature