Lysine-NPS are used for the determination and colony count of “wild yeasts” in beverages, i.e. in beer. The formulation is acc. to Morris and Eddy, modified. Wild yeasts are able to use lysine as sole source of nitrogen. Pitching yeasts used e.g. in the brewery industry do not have that ability. Hence, the detection of a wild yeasts contamination within a yeast culture sample is possible by using Lysine-NPS. Important is that after filtration of the sample and before placing the membrane onto the pad the membrane filter is washed with sterile saline or another nitrogen-free buffer, in order to eliminate all present nitrogen residues. The low pH – value inhibits the development of accompanying bacteria. The medium is manufactured and quality tested in compliance with ISO 11133:2014 standard.