Flat-sour spoilage of food

This is a type of spoilage in which the food becomes highly acid but often appears normal and shows no gas formation. The bacteria responsible for flat sour spoilage are a species of bacillus and may be found in sugar and on unsterile equipment.

The spoilage occurs mainly in low acid foods such as vegetables caused by a special thermophilic species. Aciduric ‘flat sours’ are facultative anaerobic sporeformers that’s seldom produce gas in spoiled products.

B. stearothermophilus and B, coagulans are the chief flat-sour thermopiles found in canned foods. B. stearothermophilus grows in the can, producing acids but without any gas production and subsequently the can does not swell.

Germination of spores occurs at high temperatures. B. coagulans grows at 25 °C but grows well in between 30 and 50 °C and it is homofermentative under anaerobic conditions and heterofermentative under aerobic conditions.

The ends of spoiled cans remain flat; hence, the term ‘flat sour’. Spoiled products have an off-flavor that has been described as ‘medicinal; or ‘phenolic’.
Flat-sour spoilage of food