Holes that form in cheeses such as emmental caused by hay particles in milk and not CO2 released by bacteria, say experts

This article is more than 5 years old

This article is more than 5 years old

After about a century of research, scientists in Switzerland have finally solved the mystery of the holes in Swiss cheese.

Despite what you may have been told as a child, the holes are not caused by mice nibbling away inside cheese wheels.

Experts from Agroscope, a state centre for agricultural research, said the phenomenon – which marks famous Swiss cheeses such as emmental and appenzell – was caused by tiny bits of hay present in the milk and not bacteria as previously thought.

They found that the mystery holes became smaller or disappeared when milk used for cheesemaking was extracted using modern methods.

“It’s the disappearance of the traditional bucket” used during milking that caused the difference, said Agroscope spokesman Regis Nyffeler, adding that bits of hay fell into the milk and then eventually caused the holes.

Agroscope said the mystery had been studied since at least 1917 when American William Clark published a detailed research and came to the conclusion that it was caused by carbon dioxide released by bacteria present in the milk.

Agroscope scientists noted that Swiss cheeses had fewer holes over the past 10 to 15 years as open buckets were replaced by sealed milking machines that “completely did away with the presence of tiny hay particles in the milk”.