A study of wild yeast and lactic acid bacteria in the brewery.

Brenner, M.W. and Hsu, W.P.

Abstract
The Schwarz Differential Medium, which suppresses growth of Saccharomyces carlsbergensis and S. cerevisiae, has been used in a study of wild yeasts. Results were gathered from 63 breweries on four continents and showed a fairly uniform contamination picture. Most samples showed negligible contamination but 14% were at a level of contamintion (0.01%) which was probably significant. The genera of the wild yeasts found were: Saccharomyces 81%; Candida 8%; Hansenula 3%; 8% were of unidentified genera. The occurrence of lactic acid bacteria in brewer's yeast was investigated using an improved Nakagawa medium. This system does not require anaerobic culture conditions and good correlation was found between this and the microscopic method. Of 50 beer samples investigated, 54% were clear of bacterial infection, 36% had Lactobacillus infection; 4% Pediococcus infection and 6% showed mixed infections.
Keywords: bacteria brewery brewing contamination lactic acid wild yeast