Why Are There Holes in Swiss Cheese?

Swiss cheese, renowned for its distinctive holes (also known as ‘eyes’), is not just a delight for the palate but also a subject of curiosity for many. These holes are a byproduct of the cheese-making process, specifically tied to the presence of bacteria that play a crucial role in fermentation.

This post delves into the fascinating science behind the formation of these holes and how they contribute to the cheese’s unique flavor and texture.

The Science Behind the Holes

The holes in Swiss cheese are the result of a natural fermentation process. During cheese production, dairy cultures are added to milk to start fermentation. Among these cultures, a bacterium called Propionibacterium freudenreichii is particularly significant for Swiss cheese varieties like Emmental or Gruyère.

This bacterium consumes the lactic acid produced by other bacteria and releases carbon dioxide gas as a byproduct. Since the cheese is solidifying during this time, the gas cannot escape and forms bubbles within the cheese mass, creating the characteristic holes.

Temperature and Time: Key Factors in Hole Formation

The size and number of holes in Swiss cheese can be influenced by several factors, primarily temperature and the duration of the aging process. The cheese is kept at a warm temperature (between 20°C to 24°C) for several weeks, allowing the Propionibacterium freudenreichii to thrive and produce more carbon dioxide.

The precise control of these conditions is crucial; too much or too little carbon dioxide can affect the size and distribution of the holes, as well as the overall texture and flavor of the cheese.

Modern Challenges and Adjustments

Interestingly, the advent of modern cheese-making techniques has led to a decrease in hole formation. This is because these methods result in a cleaner raw milk, with fewer naturally occurring bacteria.

To address this, cheese producers have adapted by adding specific bacterial cultures to the milk to ensure the development of holes, maintaining the traditional appearance and quality of Swiss cheese.


The holes in Swiss cheese are not just an aesthetic feature; they are a testament to the complex interplay of biology and chemistry in food production. The traditional methods and careful cultivation of specific bacteria types underscore the art and science behind cheese-making.

So, the next time you enjoy a slice of Swiss cheese, you’ll know that its holes tell a story of tradition, precision, and scientific wonder.