Methods were developed for detecting zymomonads in beer and brewing materials to and the microbiological quality control of beer and to investigate the incidence and survival of zymomonads in the brewery and public house. 1. In the cultural method the composition of a malt extract-yeast extract-glucose-peptone medium was adjusted to inhibit the growth of other spoilage micro-organisms, so that beer, raw materials, waste materials, and soil could be sampled for zymomonads. The presence of zymomonads is indicated by gas production in this medium. This test is reasonably specific for zymomonads, and can detect 1 - 5 cells/ml. 2. The serology of some zymomonads was investigated, and a specific antiserum for Zymomonas anaerobia prepared. Sampling methods were developed to allow the detection of zymomonads by immunofluorescent staining. The minimum detectable concentration was between 160 - 2500 cells/ml depending on the nature of the sample. 3. The incidence of Zymomonas anaerobia in beer, raw materials and waste materials at three breweries was investigated. It was only found in areas contaminated with infected beer. Subsequent experiments showed that Zymomonas anaerobia did not survive in soil beyond two weeks. However it persisted in brewery plant, causing acetaldehydic taints in beer. The effect of other spoilage microorganisms on acetaldehyde production by Zymomonas anaerobia was investigated. Zymomonas anaerobia remained viable for up to 36 days on steel plate at 28°C, but not at 4°C. At both temperatures the viability was influenced by the relative humidity of the atmosphere. 4. The incidence of zymomonads in selected licensed premises was investigated. Zynomonas anaerobia was a minor contaminant in 40% of the samples inspected. One sample contained an organism which was tentatively identified as Zymomonas mobilis.
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