The paper describes the use of crystal-violet and lysine containing media to detect yeast infection in brewing and to classify it. The crystal-violet containing medium helps to separate brewing yeast Saccharomyces cerevisiae and Saccharomyces carlsbergensis from wild yeast of the Saccharomyces genus, whereas the lysine containing medium--from wild yeast of the genera Candida, Debaryomyces, Brethanomyces, Pichia. The test has been used both on museum cultures and on yeast isolated from beer and non-alcoholic beverages.