Everyone knows that Swiss cheese has holes, but exactly how the holes got there in the first place is much less clear — that is, until now. Scientists may have finally solved the mystery of why Swiss cheese has holes, and more importantly, why these holes have begun to recently disappear. It turns out that tiny bits of hay are at the root of this age-old dilemma.

The holes in Swiss cheese are believed to be a by-product of tiny bits of hay which become trapped in the milk used in the cheese's production, The Guardian reported. Traditionally, buckets carried the milk that was eventually used in the cheese-making process. By default of being in the presence of open farm air, these buckets usually picked up tiny particles of hay. During the cheese-maturing process, the hay then formed the large holes which give Swiss cheese its distinctive look. To test this hypothesis, researchers at the Agroscope agricultural research center in Switzerland added a small amount of hay dust to milk used to make cheese. However, their research is not yet peer-reviewed, the BBC reported.

Over the past decade or so, cheese manufacturers have noticed that their traditional Swiss cheese was beginning to lose it signature holes — or eyes, as they are called in the cheese industry. According to Regis Nyfeler, a spokesman for Agroscope, the reason for this was the “disappearance of the traditional bucket” used during milking. In the past 10 to 15 years, sealed milking machines have replaced these buckets, and as a result, the milk no longer contained particles of hay and the cheese no longer formed holes.

This finding also disproves the previous hypothesis that the holes in Swiss, Emmental, and Appenzell-type cheese was caused by carbon dioxide given off by bacteria, a hypothesis which has been accepted as truth by most scientists since William Clark published his research on the subject in 1917.

With or without “eyes,” Swiss cheese is still one of the more healthy types of cheeses to include in your diet. A 1-ounce serving of Swiss cheese packs an impressive amount of protein and is lower in fat and sodium than other cheeses, such as cheddar, according to Live Strong. Swiss cheese, like all dairy products, is also high in calcium and phosphorus, two minerals found to help promote healthy bones.