how are holes in swiss cheese made

Holes in Swiss cheese, also known as "eyes," are formed by carbon dioxide gas bubbles produced during the fermentation process. Here’s a step-by-step explanation of how they’re made:

1. Bacterial fermentation: Swiss cheese is made from cow’s milk, which contains bacteria like Propionibacterium freudenreichii. These bacteria are added to the milk during the cheese-making process and feed on the lactose (milk sugar) in the milk.
2. Carbon dioxide production: As the bacteria ferment the lactose, they produce carbon dioxide gas as a byproduct. This process is similar to how yeast produces carbon dioxide during bread fermentation.
3. Gas bubbles form: The carbon dioxide gas gets trapped in the cheese, forming small bubbles. These bubbles are initially tiny and dispersed throughout the cheese.
4. Aging process: The cheese is then aged, which allows the bacteria to continue fermenting and producing more carbon dioxide. The cheese is typically aged at a temperature between 10°C to 15°C (50°F to 59°F), which is ideal for bacterial growth.
5. Bubble growth and coalescence: As the cheese ages, the bubbles grow and merge with each other, forming larger holes. The size and distribution of the holes depend on factors like the type of bacteria, aging time, and temperature.
6. Eye formation: The holes, or "eyes," can range in size from a few millimeters to several centimeters in diameter. The largest eyes are typically found in Emmental-style Swiss cheese, which is aged for a longer period.

It’s worth noting that not all Swiss cheese has holes. Some types, like Gruyère, have a more dense texture and fewer holes due to differences in the cheese-making process and bacterial cultures used.

In summary, the holes in Swiss cheese are a natural result of the bacterial fermentation process, which produces carbon dioxide gas bubbles that get trapped in the cheese and grow into larger holes during the aging process.