Here's Why the Holes in Swiss Cheese Are Disappearing

The most defining physical characteristic of Swiss cheese — its holes — has been disappearing over the last 15 years. But why?

Photo credit: Shutterstock

Scientists have discovered that the milk, thanks to modern milking and cheese-making techniques, is too clean.

The Swiss government-funded Agroscope Institute discovered that tiny pieces of hay dust are responsible for the famous holes in cheeses like Emmentaler or Appenzeller. As milk matures into cheese, these "microscopically small hay particles" help create the holes in the traditional Swiss cheese varieties.

Agroscope explained in a news release (translated via Google Translate) that traditional milking in the barn, when it was sprayed from the cow's udder into open buckets, allowed hay particles into the mix. Modern milking closed off the process, eliminating the microparticles.

Agroscope researchers showed that they could "practically control the opening of the cheese at will," meaning they could actually regulate the number of holes.

For more than a century, scientists had assumed that carbon dioxide produced by bacteria in the cheese-making process created the holes. Chemist William Clark wrote as early in 1917 that Swiss cheese appeared to be "seeded."

"There is really little reason, as well as little evidence, to support the assumption that the gas necessarily separates as gas bubbles where it is produced. It is not at all irrational to suppose that the gas, having first saturated the cheese mass, separates at advantageous points which have no necessary relation to those localities rich in bacterial growth. In other words we may suppose a process similar to the growth of crystals to take place," he wrote.

Live Science, which reported a few years ago about bacteria contributing to the holes, noted that in the U.S. specifically, the holes in Swiss cheese seem to have shrunk over the years because the Department of Agriculture regulates the size so it won't clog slicers in the deli.

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The Associated Press contributed to this report. Front page image via Shutterstock.