Flat-sour spoilage of canned foods is typically caused by the organisms Bacillus coagulans (Bacillus thermoacidurans). B. coagulans is ubiquitous in soil and can be found in spoilage of tomato and dairy products. Its growth in canned food products results in a decrease in the pH of the food products resulting in food spoilage, but unlike spoilage with other organisms, the ends of the can(s) remain flat.
Dextrose Tryptone Agar can be used to isolate Bacillus coagulans and other mesophilic or thermophilic microbes responsible for food spoilage. Casein peptone provides carbon, nitrogen, and necessary vitamins. Dextrose is included as the carbohydrate source. Agar serves as the solidification agent. The inclusion of Bromocresol Purple serves as a pH indicator. Recovered flat-sour thermophiles result in a decreased pH and form yellow colonies.