Which bacterium is used to produce Swiss-type cheese flavor and its characteristic holes?

Propionibacterium freudenreichii is used to produce Swiss-type cheese flavor and its characteristic holes.

During the warm stage of Swiss cheese production, this bacterium converts lactic acid into propionic acid, acetic acid, and carbon dioxide. The acids contribute to the cheese’s distinctive nutty flavor, while carbon dioxide collects in pockets and creates the holes traditionally called eyes.

The species was formerly known as Propionibacterium shermanii in cheese-making contexts and is now classified as P. freudenreichii. It is a Gram-positive, anaerobic-to-aerotolerant bacterium associated with dairy environments. Cheese makers control temperature, salt, acidity, and ripening time to guide its activity.

The holes are not produced by trapped air whipped into the curd. They mainly result from microbial carbon dioxide released during fermentation. Swiss-type cheeses can vary greatly in hole size, and modern production may produce smaller or fewer eyes because of changes in milk quality and processing.