Why are There Tiny Holes in Swiss Cheese? Researchers Have Finally Solved The Mystery

Visualize this. Inside a dairy farm, a dairy cow is moved into an open spot, her udder, a.k.a. the milk bag, is cleaned with towels dipped in iodine solution, and some hay is placed in front of her, so she will happily let down her milk. The farmer then squats down and starts squeezing her udder to force the milk out of her teats, explains the University of Florida. Meanwhile, the cow munches on the hay, oftentimes sticking some flakes to her body; some of which end up falling into the milk bucket. When this milk reaches the cheesemaking factory, the hay particles get embedded as uninvited guests in blocks of cheese. This, scientists believe, is the secret to holes found in Swiss cheese, as they revealed in a 2015 report published in the International Dairy Journal. Hay is the real culprit, not the mice!

The report, documented by researchers from Agroscope, a governmental agriculture research group, solved the longstanding “Swiss cheese mystery.” The mystery has puzzled scientists since 1917, when an American scientist hypothesized that the holes were blasted into the cheese by carbon dioxide bubbles emitted by bacteria lurking in the milk, as the Discovery Channel also explained in this Instagram post. Dubbed “eyes” by cheesemakers, these holes were mostly discovered in cheeses like Emmental and Appenzell. But the mystery of how and when they got there remained unsolved.

It wasn’t until Swiss laboratory researchers carried out this experiment that the answer was revealed. They added various amounts of powdered hay as the cheese ripened and then diced it open. They found that the mysterious holes appearing in slices and hunks of Swiss cheese are actually caused by tiny flecks of hay present in the milk at the time of cheesemaking, contrary to bacteria as previously thought. The more the hay was there in the milk, the more hole-y was the cheese. “We reasoned that hay and grass feeding could affect the entry of microparticles into raw milk and hypothesised that dust particles originating from hay could act as highly effective eye nuclei and induce the formation of eyes in cheese,” the team noted in the paper. 

They believed that the capillary structures inside particles of hay dust could be responsible for the formation of holes in the cheese. Daniel Wechsler, one of the authors involved in the study, was surprised to find that the answer to this century-old riddle turned out to be so obvious and simple. "After spending several years on that topic, the discovery of the magic effect of traces of hay dust on eye formation was for the whole team somehow just an enlightenment. The solution is so simple, it’s almost incredible that this mystery remained unsolved until nowadays," Wechsler told ABC News.

However, as modern milking methods came into the picture, the milk used to make cheese became more and more filtered. Due to lower microbial contamination, the hay falling in the milk became less and lesser in quantity. Consequently, the holes or “eyes” that earlier popped up in the cheeses became less and less prevalent. In recent days, therefore, scientists have been observing the phenomenon of “disappearing eyes” in Swiss cheese. “It’s the disappearance of the traditional bucket used during milking that caused the difference,” an Agroscope spokesman, Regis Nyffeler, told The Guardian.

As a result, the cheeses nowadays stocked in the freezer aisles of supermarkets are usually without eyes, meaning they are considered blind cheeses. Meanwhile, after making the discovery, Wechsler became so excited that he felt like celebrating it. Expressing his sentiment to ABC News, he said, "It feels just like 'Say cheeeeeeeeeeeeeeeeeeeeeeeeeese.'"