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Which bacteria help give Swiss cheese its flavor and holes?

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Bacteria A scanning electron micrograph of gram-positive *Mycobacterium tuberculosis* bacteria, the cause of tuberculosis and scrofula.

The characteristic holes (or "eyes") and flavor of Swiss-style cheeses, such as Emmentaler, are primarily developed through the use of specific bacteria during the ripening process.12

While pure cultures of Streptococcus thermophilus and Lactobacillus bulgaricus are used to control acid development and flavor, the bacterium Propionibacterium shermanii is largely responsible for the formation of the holes. During a secondary fermentation stage in a warm curing room, these propionic acid bacteria consume residual lactates and generate carbon dioxide gas. This gas becomes trapped within the firm curd, creating the iconic glossy eyes. The cheese is later moved to a cold room to finish aging, which allows it to develop its signature sweet, nutty flavor.12