What causes holes in Swiss cheese?

The holes in Swiss cheese, also known as "eyes," are caused by carbon dioxide gas produced by propionic acid bacteria during the cheesemaking process.

Here's how it works:

1. Propionic acid bacteria are added to the milk during the cheesemaking process.

2. These bacteria consume lactic acid, a byproduct of the fermentation process that gives cheese its tangy flavor.

3. As they consume lactic acid, the bacteria produce propionic acid and carbon dioxide.

4. The carbon dioxide gets trapped in the cheese curd, forming the characteristic holes.

The size and number of holes in Swiss cheese depend on several factors, including:

* Type of bacteria: Different strains of propionic acid bacteria produce varying amounts of carbon dioxide.

* Temperature and humidity: Higher temperatures and humidity encourage bacterial growth and gas production, resulting in larger and more numerous holes.

* Salt content: High salt content can inhibit bacterial growth and reduce the number of holes.

So, the next time you enjoy a slice of Swiss cheese, remember to thank the propionic acid bacteria for those delicious holes!