MYGP + COPPER, A MEDIUM THAT DETECTS BOTH SACCHAROMYCES AND NON-SACCHAROMYCES WILD YEAST IN THE PRESENCE OF CULTURE YEAST*

Lin's copper sulphate medium for the detection of non-Saccharomyces wild yeast was modified, mainly by reducing the concentration of copper sulphate, with the aim of producing a medium that could detect a wide range of both non-Saccharomyces and Saccharomyces wild yeast. The performance of the resultant MYGP + Cu medium was compared to that of crystal violet and lysine media using pure cultures of wild yeast, pitching yeast and brewery samples. The growth of the pitching yeasts examined was suppressed more in MYGP + Cu than in crystal violet and the 4 ale yeasts were more susceptible to copper inhibition than the 3 lager yeasts. Neither MYGP + Cu nor crystal violet could detect all the wild Saccharomyces species tested but the proportion detected by each was similar. Twenty-seven out of 28 non-Saccharomyces wild yeasts tested could be detected in MYGP + Cu. When brewery samples were examined, the detection rate by MYGP + Cu compared favourably with that by a combination of crystal violet and lysine. MYGP + Cu is particularly suited to the monitoring of the production of cask-conditioned ales.