Glucose M9Y is an APF Certified™ minimal media formulation supplemented with yeast extract for the cultivation of E. coli. It is based on M9 salts with a pH of 6.9 ± 0.2 and employs glucose as the carbon source1. Buffering is provided by a sodium-potassium phosphate system. Ammonium chloride provides a nitrogen source. Yeast extract is added to improve the protein production capacity of the medium and to permit cultivation of auxotrophic strains by supplying a source of amino acids, vitamins and minerals. Our formulation differs from the traditional formulation of Glucose M9, which employs casamino acids. Our experience has shown that yeast extract typically gives higher yields of recombinant proteins than casamino acids.