What gives Swiss cheese wholes?

The holes in Swiss cheese, often called "eyes", are formed by carbon dioxide gas. This gas is produced by propionibacterium freudenreichii, a type of bacteria added to the milk during the cheesemaking process.

Here's a breakdown of how it happens:

1. Bacteria and Milk: The bacteria feed on the lactose (milk sugar) in the milk and produce propionic acid as a byproduct.

2. Gas Production: During this process, they also produce carbon dioxide gas.

3. Hole Formation: As the cheese matures, the carbon dioxide gas builds up within the cheese curds, forming bubbles. These bubbles become the characteristic "eyes" of Swiss cheese.

The size and number of holes can be influenced by factors like:

* Type of bacteria: Different strains of Propionibacterium freudenreichii can create varying hole sizes.

* Temperature and humidity: The temperature and humidity during aging affect the rate of gas production.

* Milk quality: The composition of the milk can also impact the amount of gas produced.

So, it's the clever combination of bacteria, milk, and aging that creates the delicious and distinctive holes in Swiss cheese!