BERN — Researchers in Switzerland say they've finally solved the mystery of why holes form in Swiss cheese. The clue is that Swiss cheese has had fewer holes in recent years because the cow's milk has gotten cleaner, reports the Swiss news agency ATS.

The researchers at Agroscope, a Swiss lab that studies food and agriculture production, dosed samples of Emmental with tiny particles of hay. Based on the amount of hay they inserted, the researchers found they could predict where and how many holes would form in the cheese.

“It’s now possible to get the cheese to open up almost exactly to your liking,” according to Thursday's press release of the findings.

Scientists have long tried to understand why holes formed in Swiss cheese. American researcher William Clark concluded in 1917 that the holes had something to do with carbon dioxide emitted by bacteria in the milk, but was ultimately unable to discern why the holes formed in some places and not others.

In recent years, pasteurization has moved to covered systems rather than open vats. Unwanted bacteria was reduced, but the holes in Swiss cheese also started to disappear.

“In addition to milk, enzymes and bacterial cultures, you need bits of hay,” the researchers conclude. “It’s a good example of how raw, unprocessed milk is still what essentially underlines the character of traditional Swiss cheeses.“

Lead photo: Gerard Lacz Images/VW Pics/ZUMA