how do they get the holes in swiss cheese

The characteristic holes in Swiss cheese are formed by carbon dioxide gas bubbles produced during the fermentation process. Here’s a simplified explanation of how this happens:

1. Microbial fermentation: Swiss cheese, such as Emmental or Gruyère, is made from cow’s milk. During the cheese-making process, microorganisms like bacteria (e.g., Propionibacterium freudenreichii) and yeast are added to the milk. These microorganisms feed on the lactose (milk sugar) in the milk.
2. Carbon dioxide production: As the microorganisms break down the lactose, they produce carbon dioxide gas (CO2) as a byproduct. This is similar to how yeast produces CO2 during the brewing process for beer.
3. Gas bubble formation: The CO2 gas bubbles form within the cheese as it ages. The bubbles can grow in size as more CO2 is produced, eventually forming larger holes or pockets.
4. Cheese expansion and contraction: As the cheese ages, it undergoes a series of temperature and humidity changes. These changes cause the cheese to expand and contract, which can lead to the formation of even larger holes.
5. Enzymatic activity: Enzymes naturally present in the cheese, such as proteases, can break down the casein proteins and create weaker points in the cheese matrix. These weaker points can become the sites where the CO2 bubbles form and expand.

The holes in Swiss cheese are an important aspect of its texture and flavor. They can affect the way the cheese melts, its moisture content, and even the distribution of flavor compounds.

Interestingly, the hole size and distribution can vary depending on the specific type of Swiss cheese, the aging process, and the microorganisms involved. Some cheeses, like Emmental, have larger holes (up to 2-3 inches in diameter), while others, like Gruyère, have smaller, more evenly distributed holes.