Evaluation of nbb anaerobic medium for beer spoilage organisms.
The quality of European NBB, modified NBB and UBA media are compared in laboratory trials and brewing practice as early indicators of anaerobic Lactobacillus and Pediococcus beer spoilage organisms, in order to avoid repitching of contaminated yeast. Modified NBB recovered 95 to 99% of the original inoculum within 3 to 4 days. UBA reached this level after 6 days. The European NBB medium did not exceed 50% recovery of the inoculum and was tested no further. The buffering capacity of mod. NBB was superior to UBA and gave reliable counts after 4 days instead of 6 for UBA. Concentrations for mod. NBB platings had to be reduced to 2.5 ml (maximum) to avoid premature colour changes. Mod. NBB exerts additional inhibition on yeast growth, when used in conjunction with actidione and left platings with a consistently less opaque background after incubation, thus facilitating enumeration. The greater selectivity of mod. NBB medium for beer spoilage organisms than UBA was confirmed in brewing trials. For practice however, application guidelines have to be strictly followed and empiric data suggest a minimum acceptable pH of 5.75 for mod. NBB.
Keywords : anaerobic beer contamination lactobacillus medium Pediococcus use