what are the holes in swiss cheese called

The characteristic holes in Swiss cheese are called “eyes.” These eyes are formed during the fermentation process when carbon dioxide gas is produced by bacteria, such as Propionibacterium freudenreichii, that are naturally present in the cheese or added during the cheese-making process.

As the bacteria break down the lactose in the milk, they produce carbon dioxide gas, which gets trapped in the cheese, forming bubbles. As the cheese ages, these bubbles expand and eventually form the characteristic holes or eyes that are typical of Swiss cheese.

The size and distribution of the eyes can vary depending on the type of Swiss cheese and the aging process. Some Swiss cheeses, such as Emmental, have large eyes, while others, like Gruyère, have smaller eyes.