Why Does Swiss Cheese Have Holes?

I always wondered growing up why Swiss cheese have holes. Is it mice chomping into the cheese or is it science? Well, to say this is a debated topic would be an understatement.

Original Theory

To understand the original theory of why Swiss cheese has holes, It is important to understand how cheese it make. Cheese types vary based on the type of milk. Once the milk is chosen, bacteria is added to cause the formation of solid “curds” and “whey.” The amount of bacteria added influences the taste of the final cheese. Swiss cheese in particular is made with cow’s milk and contains bacteria. So why does Swiss cheese have holes? An additional bacteria called Propionibacterium freudenrichii subspecies shermanii is added to the product. The bacteria produces carbon dioxide that causes bubbles in the cheese. These bubbles “pop” and cause holes. in the product. This theory was developed by chemist William Mansfield Clark.

Hay Theory

The new theory was created by a Swiss agricultural institute named Agroscope that believes that hay particles cause the holes in cheese. Cheese Is made in barns and there is a possibility that hay could make it into the milk. The specks of hay causes gas to form and create the “eyes.”

https://jov.arvojournals.org/article.aspx?articleid=2191677

https://www.sciencedirect.com/science/article/pii/S0022030217943620

https://www.jstor.org/stable/30083493?seq=1