Detection of Mixtures of Lager Yeast Strains by the Use of Selective Inhibitors in Solid Media

The use of more than one lager yeast strain in a brewery poses the risk of cross-contamination with consequent problems in beer quality. In this work, conditions are reported that allow the detection of cross-contamination among three lager yeast strains used in this company's breweries by the use of selective inhibitors in solid media. The inhibitors used were bromocresol green, copper sulfate, basic fuchsin, streptomycin, and Actidione (cycloheximide). Contamination levels as low as 0.01% (one in 10,000) were detected in some cases.