The holes in Swiss cheese form when bacteria release gas during the aging process.

The longer version

Those round openings are pockets of carbon dioxide released by bacteria working inside the aging cheese. During warm ripening, certain cultures consume lactate and produce gas; because the cheese mass is elastic and sealed by its rind, the gas cannot escape and instead collects wherever it can. The size and number of openings depend on temperature, acidity, and how the curd was pressed.

Cheesemakers control the effect by adjusting the starter cultures, the cooking temperature of the curd, and the length of the warm room stage. Holes that look split or wet suggest the gas formed faster than the surrounding paste could stretch. Similar gas formation happens in other long-aged cheeses, though the openings there are usually far smaller.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.