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What’s Happened to the Holes in Swiss Cheese?

Last Modified Date: January 27, 2024

In 1917, American researcher William Clark theorized that the holes in Swiss cheeses, such as Emmental, were the result of carbon dioxide released by bacteria in the milk. Now, more than a century later, scientists in Switzerland have a rebuttal of sorts.

Cheese aficionados have long known that the holes (technically known as "eyes") in Swiss cheese have become smaller and less plentiful over the years. Experts say that’s because modern cheesemaking methods have become cleaner. Researchers at the Swiss agricultural research facility Agroscope have concluded that the holes were caused by impurities in the milk – specifically, tiny specks of hay.

Poking holes in the cheesemaking process:

In earlier times, researchers say, the holes were larger and more prevalent because of the presence of tiny bits of hay in the milk.

Traditionally, milking took place by hand, with milk squirted into buckets under a cow’s udder. Now, the extraction process involves machines transferring fluid directly from an animal’s teats into sealed containers.

However, the new theory about holes doesn't discount carbon dioxide as a partial cause. The bits of hay were "the perfect shelter for bubbles of CO2." Carbon dioxide is still causing holes to develop – they’re just smaller now.