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Late Gas Defect in Cheddar Cheese Caused by an Unusual Bacterium¹

Food Research Institute, Research Branch, Agriculture Canada, Ottawa, K1A OC6, Canada

ABSTRACT

Several instances of gas formation without noticeable texture changes were noted in Canadian Cheddar cheese aged between 9 and 12 mo. The bacterium considered responsible was a gram-positive, asporogenous, pleomorphic, slow-growing anaerobic rod capable of reducing nitrate. The organism gave negative tests for catalase, indole, and urease and was capable of surviving the thermal processing normally given to milk prepared for Cheddar manufacture. A major feature of the organism was its slow growth. The bacterium required 4 days or more at 32°C to produce pinpoint colonies. Experimental Cheddar made with milk inoculated with either 10 cells/ml or 10,000 cells/ml of the suspect organism developed the atypical late gas defect between 6 and 10 mo when stored at 10°C but not when stored at 4.5°C for 1 yr. The identity of the organism responsible is unknown, and the extent of the problem in industry should be defined.

¹ Scientific contribution Number 447 from the Food Research Institute.