SUMMARY Growth curves were obtained for numbers of organisms surviving on beef stored at 0°, 5°, 10°, 15°, 20° and 25° C. These were related to the development of off‐odor and slime. It was shown that the initial load of organisms determined the time required for development of slime. The critical value for slime production was found to be 6 × 107 organisms or a log value of 7.8. There was a change in slope for the effect of temperature at 0° C when compared with that of 20° C. Comparison was made of the swab, rinse and cut‐section methods of sampling; swab samples were selected as being the most reproducible and most convenient to use. The effect of storage time and temperature on percentages of lipolytic, gelatin liquefying, oxidase producing, chromogenic and fluorescent bacteria was studied. Most of the bacteria on stored meats had lipolytic activity; from one‐third to two‐thirds of the organisms liquefied gelatin. Oxidase production could not be determined accurately. From 4‐20% of the initial population were found to be chromogens but colored colonies were rarely found beyond the fourth day of storage; also, plates stored at temperatures less than 15° C did not yield chromogens. Fluorescent bacteria comprised 10‐25% of the flora throughout storage. Microorganisms isolated from refrigerated beef were classified and it was found that at 10° C or lower the bacteria responsible for production of slime were almost without exception pseudomonads. Various species of Pseudomonas were identified. At 15° C or above, there was approximately an equal incidence of organisms of the genus Micrococcus and Pseudomonas. Other bacteria that were recovered from the sliced meat were Achromobacter, Flavobacterium, Microbacterium, Alcaligenes, Aeromonas, Bacillus, Clostridium and Streptococcus. Species of Penicillium were the most commonly encountered molds, more rarely, Cladosporium, Thamnidium, Mucor, Rhizopus, Aspergillus, Alternaria, and Sporotrichum were found.

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